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182402.00 / 187116.00 ● Final Report ● March 2020
Environmental Risk Assessments & Preliminary
Design of Seven Future Wastewater
Treatment Systems in CBRM
Donkin Wastewater Interception & Treatment System
Preliminary Design Summary Report
Prepared by:
Prepared for:
Donkin WW Interception &
Treatment System Preliminary Design
Summary Report-Draft
March 27, 2020 Darrin McLean James Sheppard Darrin McLean
Issue or Revision Date Issued By: Reviewed By: Prepared By:
This document was prepared for the party indicated
herein. The material and information in the
document reflects HE’s opinion and best judgment
based on the information available at the time of
preparation. Any use of this document or reliance
on its content by third parties is the responsibility of
the third party. HE accepts no responsibility for any
damages suffered as a result of third party use of
this document.
164 Charlotte St.
PO Box 567
Sydney, NS
B1P 6H4
March 27, 2020
Matt Viva, P.Eng.
Manager Wastewater Operations
Cape Breton Regional Municipality (CBRM)
320 Esplanade,
Sydney, NS B1P 7B9
Dear Mr. Viva:
RE: Donkin Wastewater Interception & Treatment System
– Preliminary Design Summary Report
Enclosed, please find, for your review, a copy of the first draft of the Preliminary Design
Summary Report for the Donkin Wastewater Interception & Treatment System.
This report presents a description of proposed wastewater interception and treatment
infrastructure upgrades for the Donkin Wastewater system, as well as an estimate of the
capital, operating costs, and replacement costs for the proposed infrastructure. In addition,
estimated costs of upgrades and assessments related to the existing wastewater collection
system are provided. Also, a desktop geotechnical review of the wastewater treatment
facility site is provided, along with an archaeological resources impact assessment review for
all sites of proposed wastewater infrastructure. Finally, an Implementation Timeline is
provided, which outlines a tentative schedule for implementation of the various proposed
wastewater system upgrades.
If you have any questions or require clarification on the content presented in the attached
report, please do not hesitate to contact us.
Yours very truly,
Harbour Engineering Joint Venture
Prepared by: Reviewed by:
Darrin McLean, MBA, FEC, P.Eng. James Sheppard, P.Eng.
Senior Municipal Engineer Civil Infrastructure Engineer
Direct: 902-539-1330 (Ext. 3138) Direct: 902-562-9880
E-Mail: dmclean@cbcl.ca E-Mail: jsheppard@dillon.ca
Project No: 182402.00 (CBCL)
187116.00 (Dillon)
HEJV Donkin Wastewater System Pre-Design Summary Report i
Contents
CHAPTER 1 Introduction & Background ........................................................................................ 1
1.1 Introduction ........................................................................................................................ 1
1.2 Background ......................................................................................................................... 1
1.3 Description of Existing Wastewater Collection System ...................................................... 1
1.4 Service Area Population ...................................................................................................... 2
CHAPTER 2 Wastewater Interceptor System ................................................................................. 3
2.1 Description of Proposed Wastewater Interceptor Infrastructure ...................................... 3
2.2 Interception Infrastructure Land/Easement Acquisition Requirements ............................ 3
2.2.1 Lift Station Sites ...................................................................................................... 3
2.2.2 Linear Infrastructure ............................................................................................... 4
CHAPTER 3 Existing Wastewater Collection System Upgrades / Assessments ................................ 5
3.1 Sewage Pump Station Upgrades ......................................................................................... 5
3.2 Asset Condition Assessment Program ................................................................................ 5
3.3 Sewer Separation Measures ............................................................................................... 5
CHAPTER 4 Wastewater Treatment System .................................................................................. 6
4.1 Recommended Wastewater Treatment Facility ................................................................. 6
4.2 Wastewater Treatment Facility Land Acquisition Requirements ....................................... 7
4.3 Wastewater Treatment Facility Site Desktop Geotechnical Review .................................. 7
CHAPTER 5 Wastewater System Archaeological Resources Impact Assessment ............................. 9
5.1 Archaeological Resources Impact Assessment ................................................................... 9
CHAPTER 6 Wastewater Infrastructure Costs .............................................................................. 11
6.1 Wastewater Interception & Treatment Capital Costs ...................................................... 11
6.2 Wastewater Interception & Treatment Annual Operating Costs ..................................... 12
6.3 Annual Capital Replacement Fund Contribution Costs..................................................... 12
6.4 Existing Wastewater Collection System Upgrades / Assessment Costs ........................... 14
CHAPTER 7 Project Implementation Timeline ............................................................................. 15
7.1 Implementation Schedule ................................................................................................. 15
Appendices
A Donkin Collection System Pre-Design Brief
B Donkin Wastewater Treatment System Pre-Design Brief
C Donkin Environmental Risk Assessment Report
D Donkin Wastewater Treatment Facility Site Desktop Geotechnical Review
E Donkin Wastewater System Archaeological Resources Impact Assessment
HEJV Donkin Wastewater System Pre-Design Summary Report 1
CHAPTER 1 INTRODUCTION & BACKGROUND
1.1 Introduction
Harbour Engineering Joint Venture (HEJV) was retained by the Cape Breton Regional Municipality
(CBRM) to provide engineering services associated with the preliminary design of wastewater
interception and treatment infrastructure for the community of Donkin, Nova Scotia as part of the
greater Environmental Risk Assessment and Preliminary Design of 7 Future Wastewater Treatment
Systems in CBRM project. This report presents a description of the proposed infrastructure upgrades
for the Donkin Wastewater system, as well as an estimate of the capital, operating and replacement
costs for the proposed infrastructure. In addition, estimated costs of upgrades and assessments
related to the existing wastewater collection system are provided. Also, a desktop geotechnical
review of the wastewater treatment facility site is provided, along with an archaeological resources
impact assessment review for all sites of proposed wastewater infrastructure. Finally, an
Implementation Timeline is provided, which outlines a tentative schedule for implementation of the
various proposed wastewater system upgrades.
1.2 Background
The wastewater collection system in the community of Donkin, as in many communities throughout
CBRM, currently discharges untreated wastewater to the Atlantic Ocean. The evolution of the existing
wastewater collection and disposal systems in CBRM included the creation of regions of a community
which were serviced by a common wastewater collection system tied to a local marine outfall. Such
design approaches have traditionally been the most cost-effective manner of providing centralized
wastewater collection, and the marine environment has long been the preferred receiving water given
the available dilution. Due to a changing regulatory environment, CBRM is working toward intercepting
and treating the wastewater in these communities prior to discharge.
The Donkin system has been classified as low risk under the federal Wastewater System Effluent
Regulations (WSER) under the Fisheries Act, requiring implementation of treatment systems by the year
2040.
1.3 Description of Existing Wastewater Collection System
The Community of Donkin is primarily serviced by a gravity sewer system, ranging in size from 200 to
375mm in diameter. There is one lift station within the existing Donkin wastewater collection system,
located on the Donkin Highway, across the street from Civic #383. The lift station was upgraded in
HEJV Donkin Wastewater System Pre-Design Summary Report 2
2010, to a Flygt fiberglass submersible station. There is an overflow from the station to an adjacent
brook. The station does not have backup power.
The existing collection system conveys sewage to a single pipe outfall located at Borden’s
Cove/Schooner Pond. The outfall is 375mm in diameter and is concrete encased. The pipe obvert is
set at the low, low water elevation and terminates approximately 31m from the shore.
1.4 Service Area Population
For Donkin, the service area population was estimated to be 471 people in 256 residential units. The
population of the CBRM has been declining and this trend is expected to continue. Recent population
projection studies predict a 17.8% decrease in population in Cape Breton County between 2016 and
2036. For this reason, no allocation has been made for any future population growth.
For the purpose of preliminary design, wastewater infrastructure has been sized based on the current
population and measured flow data. While this may seem overly conservative, due to significant
amounts of inflow and infiltration (I&I) observed in sewer systems in the CBRM, a given population
decrease will not necessarily result in a proportional decrease in wastewater flow. Therefore, basing
the design on current conditions is considered the most reasonable approach.
HEJV Donkin Wastewater System Pre-Design Summary Report 3
CHAPTER 2 WASTEWATER INTERCEPTOR SYSTEM
2.1 Description of Proposed Wastewater Interceptor Infrastructure
The proposed wastewater interceptor system for the Donkin Wastewater System includes the
following major elements:
A new sewage pumping station will be constructed near the end of Bastable Street, which will
redirect flow from the existing outfall to the proposed WWTP.
Treated flow will be conveyed back to the existing outfall via a 375 mm diameter gravity
sewer.
A detailed description of the proposed wastewater interceptor system, including preliminary layout
drawings is provided in Appendix A.
2.2 Interception Infrastructure Land/Easement Acquisition Requirements
2.2.1 Lift Station Sites
Construction of a new sewage pumping station and WWTP access road will require a property
easement on land privately owned by Simon Edward Baxter as shown in Table 1 below. The
installation of the linear infrastructure and access road will also require acquisition of another parcel
of land privately owned by Simon Edward Baxter as shown in Table 2. It should be noted that the
same parcel of land is required for construction of the proposed WWTP.
Table 1 - Lift Station/Access Road Site Land Easement Requirements
PID# Property
Owner Assessed Value Description Purchase Entire
Lot (Y/N)
15064694 Simon Edward
Baxter $4,900 Access Road
Lift Station N
Table 2 – Linear Infrastructure/ Access Road/ WWTP Site Land Acquisition Requirements
PID# Property
Owner Assessed Value Description Purchase Entire
Lot (Y/N)
15494248 Simon Edward
Baxter $7,600
WWTP / Access
Road/ Linear
Infrastructure
Y
HEJV Donkin Wastewater System Pre-Design Summary Report 4
2.2.2 Linear Infrastructure and Access Road
Installation of remaining linear infrastructure such as new gravity sewer piping and manholes will not
require property acquisition as these features are to be installed on property already owned by the
CBRM.
HEJV Donkin Wastewater System Pre-Design Summary Report 5
CHAPTER 3 EXISTING WASTEWATER COLLECTION SYSTEM UPGRADES / ASSESSMENTS
3.1 Sewage Pump Station Upgrades
HEJV has reviewed the existing Donkin Collection System for potential upgrades to the existing sewage
pumping stations. There is currently one pump station in the community of Donkin, which was
upgraded in 2010. The Donkin WWTP has been classified as a low priority system and has an
implementation deadline of 2040. Considering that 2040 is 21 years in the future, plans should be
made to upgrade the existing pump station as part of the interception work to be completed in the
community. Due to age, the necessity to upgrade the existing station may occur prior to the
implementation of the interceptor sewer project. Therefore, the condition of the station should be
verified at the time of detailed design to determine if an upgrade is required.
3.2 Asset Condition Assessment Program
To get a better sense of the condition of the existing Donkin sewage collection system, HEJV
recommends completing a sewage collection system asset condition assessment program in the
community. The program would carry out an investigation involving two components:
1. Visual inspection and assessment of all manholes in the collection system;
2. Video inspection of 20% of all sewers in the system
The program should be completed with the issuance of a Collection System Asset Condition
Assessment Report that would summarize the condition of the various assets inspected and include
opinions of probable costs for required upgrades.
3.3 Sewer Separation Measures
CBRM should consider completing further sewer separation investigation efforts in Donkin. The
program would review catch basins that are currently connected or possibly connected to existing
sanitary sewers. The program should also include the costing of the installation of new storm sewers
to disconnect catch basins from the existing sanitary sewer.
HEJV Donkin Wastewater System Pre-Design Summary Report 6
CHAPTER 4 WASTEWATER TREATMENT SYSTEM
4.1 Recommended Wastewater Treatment Facility
The recommended wastewater treatment facility for Donkin is an aerated lagoon system. In aerated
lagoons, oxygen is supplied by mechanical aeration, which in newer systems is typically subsurface
diffused aeration. They have average retention times ranging from 5 to 30 days, with 30 days being
common in Atlantic Canada. The WWTP would provide the following general features:
1. Preliminary treatment involving a manually-cleaned bar screen;
2. Secondary treatment involving three aerated lagoon basins divided into four aerated cells and
one quiescent settling zone by means berms or floating baffles;
3. An aeration system consisting of blowers and low pressure air distribution piping;
4. Disinfection of the treated wastewater with the use of an ultraviolet (UV) disinfection unit;
5. A small process building to provide space for blowers, UV disinfection equipment, basic office
space, laboratory space, instrumentation equipment, and a washroom;
6. Permanent backup power supply generator;
7. Site access and parking, along with site fencing; and,
8. Extension of the existing outfall pipe.
The proposed site of the Donkin WWTP is located near the end of Bastable Street in Donkin. The
design loads for the proposed WWTP are as shown in the table below.
Table 2 - WWTP Design Loading Summary
Parameter Average Day Peak Day
Design Population 471
Flow (m3/day) 360 400
CBOD Load (kg/day) 38 46
TSS Load (kg/day) 42 50
TKN Load (kg/day) 6 8
A detailed description of the proposed wastewater treatment system, including preliminary layout
drawings is provided in Appendix B.
HEJV Donkin Wastewater System Pre-Design Summary Report 7
The associated Environmental Risk Assessment Report, which outlines effluent criteria for the
proposed wastewater treatment facility for Donkin is provided in Appendix C.
4.2 Wastewater Treatment Facility Land Acquisition Requirements
Construction of the proposed wastewater treatment facility will require property acquisitions as
shown in the table below.
Table 3 – LS/WWTP Land Acquisition Requirements
PID# Property
Owner Assessed Value Description Purchase Entire
Lot (Y/N)
15494248 Simon Edward
Baxter $7,600 WWTP Y
4.3 Wastewater Treatment Facility Site Desktop Geotechnical Review
A desktop review of the geotechnical conditions was carried out for the WWTP. The review was
completed prior to finalizing the preliminary design study, and focused on the property immediately
adjacent to the site that was ultimately proposed for the WWTP. However, the general observations
made in the report are likely also applicable to the adjacent property. As the report recommended
intrusive geotechnical investigation prior to detailed design, the desktop study will not be revised at
this time. In general, the review involved a field visit to the site to observe the general conditions and
a desktop review of available documents with the intent of commenting on the following issues:
site topography;
geology (surficial ground cover, probable overburden soil and bedrock type);
geotechnical problems and parameters;
previous land use (review of aerial photographs);
underground/surface mining activities; and
proposed supplemental ground investigation methods (test pits and/or boreholes)
The following geotechnical issues were noted in the report:
1. There is evidence of the erodibility of subsurface soils and bedrock exposure along the Atlantic
coastline and a Coastal Protection Plan will be required for the site.
2. The area southwest of the proposed construction site was undermined due to historical coal
mining activities and there is a potential for undocumented bootleg pits/mines in the area.
3. There is the potential for a layer of limestone to be present underlying the surficial ground
and alternating layers of bedrock below the site. Limestone is water soluble and has the
potential to develop karsts voids (sinkholes).
4. It is anticipated that the overburden soil will be in a very moist to wet condition near the
surface, in particular near marshy/boggy areas on the site. This will create some problems
during site preparation and construction. A Surficial and Groundwater Control Plan should be
developed for the site.
5. The presence of uncontrolled fills is suspected on the southern corner of the site due to
historical activities on the site for the installation of a sanitary sewer discharge line into the
harbour.
HEJV Donkin Wastewater System Pre-Design Summary Report 8
The review recommends an intrusive borehole program on the site to further define the subsurface
conditions including verifying the presence or absence of authorized and/or bootleg mining activities
undertaken in the area, as well as the potential of future subsidence that could impact structures
constructed on the site. The goal of the supplemental geotechnical ground investigation would be to
collect pertinent information pertaining to the subsurface conditions within the footprint of the
proposed new facility. This information would then be used to develop geotechnical
recommendations for use in the design and construction of the new facility.
The report recommended that borehole locations be selected based upon the location of buried
infrastructure and to provide adequate coverage of the site. It recommended that representative
soil samples be collected continually throughout the overburden material of each of four boreholes
advanced at the site. Additionally, it is recommended that during the investigation samples of the
bedrock should be collected continuously to a depth of at least 30 metres or more, in two of the
four boreholes. The intent of the bedrock coring would be to:
verify the presence or absence of underground mine workings (both authorized commercial
activities and/or bootleg pits);
increase the odds of advancing the borehole through the roof of any mine working (to
determine the potential void space) and not into a supporting pillar (if applicable); and
accurately characterize the bedrock for design of either driven or drilled piles, if needed.
It recommended that the remaining two boreholes be terminated either at 12 metres depth below
ground surface or once refusal on assumed bedrock is encountered (whichever comes first). It should
be noted that if pillar extraction took place, fractures will likely extend 20 metres above mine
workings. If this is the case, drill return water may be lost and rock wedges may be encountered. This
would inhibit coring and an alternative method of drilling through fractured rock may have to be
pursed.
A copy of the Donkin WWTP site geotechnical review report is provided in Appendix D.
HEJV Donkin Wastewater System Pre-Design Summary Report 9
CHAPTER 5 WASTEWATER SYSTEM ARCHAEOLOGICAL RESOURCES IMPACT ASSESSMENT
5.1 Archaeological Resources Impact Assessment
Davis MacIntyre & Associates Limited has conducted a phase I archaeological resource impact
assessment at sites of proposed wastewater infrastructure for the Donkin Wastewater System.
The assessment included a historic background study and reconnaissance in order to determine the
potential for archaeological resources in the impact area and to provide recommendations for further
mitigation, if necessary.
The assessment found that much of the study area is wetland interspersed with a few forested areas.
However, the field reconnaissance did indicate one area where potential historic cultural resources
may be present at the end of an old road and beyond a levelled clearing. The clearing may have been
the site of an earlier structure which may have been demolished and the surrounding area levelled.
Beyond the treeline, two probable cultural depressions were noted which lie within the proposed
impact area. Avoidance is always the preferred method of mitigation where impact to archaeological
resources is possible. If avoidance is not possible, it is recommended that the area surrounding the
earthen depressions be subjected to subsurface testing at 5-meter intervals in order to determine the
significance, age, and/or function of these features.
The proposed Donkin WWTP development site falls within zones that are known for prevalent
Carboniferous fossil flora, and there is a possibility that fossil fauna may be present as well in rare
instances. Although fossils as well as archaeological material fall under the Special Places Protection
Act, as archaeologists rather than paleontologists it is difficult to accurately state the possible
significance of these fossil flora and rare fossil fauna. It is recommended that, if available, a qualified
palaeontologist or geologist be contracted to examine any bedrock exposed during the project
excavation, and to determine the need for any further paleontological monitoring.
If additional areas that were not assessed are expected to be impacted, the study recommended that
an assessment of the new impact area be conducted. If any archaeological resources are encountered
at any time during ground disturbance, it is required that all activity cease and the Coordinator of
Special Places (902-424-6475) be contacted immediately regarding a suitable method of mitigation.
HEJV Donkin Wastewater System Pre-Design Summary Report 10
The study recommended that, if available, a qualified palaeontologist or geologist be contracted to
examine any bedrock exposed during the project excavation, and to determine the need for any
further paleontological monitoring.
HEJV Donkin Wastewater System Pre-Design Summary Report 11
CHAPTER 6 WASTEWATER INFRASTRUCTURE COSTS
6.1 Wastewater Interception & Treatment Capital Costs
An opinion of probable capital cost for the recommended wastewater interception and treatment
system for Donkin is presented in the table below.
Table 4 - Donkin Wastewater Interception & Treatment System Capital Costs
Project Component Capital Cost (Excluding
Taxes)
Wastewater Interception System $411,780
Wastewater Interception System Land Acquisition $10,000
Subtotal 1: $421,780
Construction Contingency (25%): $103,000
Engineering (10%): $42,000
Total Wastewater Interception: $566,780
Wastewater Treatment Facility $6,130,000
Wastewater Treatment Facility Land Acquisition $12,500
Subtotal 2: $6,142,500
Construction Contingency (25%): $1,533,000
Engineering (12%): $736,000
Total Wastewater Treatment: $8,411,500
Total Interception & Treatment System: $8,978,280
HEJV Donkin Wastewater System Pre-Design Summary Report 12
6.2 Wastewater Interception & Treatment Annual Operating Costs
An opinion of probable annual operating costs for the recommended wastewater interception and
treatment system for Donkin is presented in the table below.
Table 5 - Donkin Wastewater Interception & Treatment System Operating Costs
Project Component Annual Operating Cost
(Excluding Taxes)
Wastewater Interception System
General Linear Maintenance Cost $500
General Lift Station Maintenance Cost $2,500
Employee O&M Cost $4,000
Electrical Operational Cost $1,000
Total Wastewater Interception Annual Operating Costs: $8,000
Wastewater Treatment Facility
Staffing $50,000
Power $13,400
Sludge Disposal $1,100
Maintenance Allowance $3,000
Total Wastewater Treatment Annual Operating Costs: $67,500
Total Interception & Treatment System Annual Operating Costs: $75,500
6.3 Annual Capital Replacement Fund Contribution Costs
The CBRM wishes to create a Capital Replacement Fund to which annual contributions would be made
to prepare for replacement of the wastewater assets at the end of their useful life. The calculation of
annual contributions to this fund involves consideration of such factors as the type of asset, the asset
value, the expected useful life of the asset, and the corresponding annual depreciation rate for the
asset. In consideration of these factors, the table below provides an estimate of the annual
contributions to a capital replacement fund for the proposed new wastewater interception and
treatment system infrastructure. This calculation also adds the same contingency factors used in the
calculation of the Opinion of Probable Capital Cost, to provide an allowance for changes during the
design and construction period. The actual Annual Capital Replacement Fund Contributions will be
calculated based on the final constructed asset value, the type of asset, the expected useful life of the
asset, and the corresponding annual depreciation rate for the asset type. Please note that costs
shown below do not account for annual inflation and do not include applicable taxes.
HEJV Donkin Wastewater System Pre-Design Summary Report 13
Table 6 - Donkin Wastewater Interception & Treatment System Capital Replacement Fund
Description of Asset Asset
Value
Asset Useful Life
Expectancy
(Years)
Annual
Depreciation Rate
(%)
Annual Capital
Replacement Fund
Contribution
Wastewater Interception System
Linear Assets (Piping, Manholes and
Other) $109,080 75 1.3% $1,418
Pump Station Structures (Concrete
Chambers, etc.) $136,215 50 2.0% $2,724
Pump Station Equipment
(Mechanical / Electrical) $166,485 20 5.0% $8,324
Subtotal $411,780 - - $12,466
Construction Contingency (Subtotal x 25%): $3,117
Engineering (Subtotal x 10%): $1,247
Wastewater Interception System Annual Capital Replacement Fund Contribution Costs: $16,829
Wastewater Treatment System
Treatment Linear Assets (Outfall and
Yard Piping, Manholes and Other) $4,446,000 75 1.3% $58,000
Treatment Structures (Concrete
Chambers, etc.) $205,000 50 2.0% $5,000
Treatment Equipment (Mechanical /
Electrical, etc.) $1,479,000 20 5.0% $74,000
Subtotal $6,130,000 - - $137,000
Construction Contingency (Subtotal x 25%): $34,250
Engineering (Subtotal x 12%): $16,440
Wastewater Treatment System Annual Capital Replacement Fund Contribution Costs: $187,690
Total Wastewater Interception & Treatment Annual Capital Replacement Fund
Contribution Costs: $204,519
HEJV Donkin Wastewater System Pre-Design Summary Report 14
6.4 Existing Wastewater Collection System Upgrades / Assessment Costs
The estimated costs of upgrades and assessments related to the existing wastewater collection
system as described in Chapter 3 are shown in the table below.
Table 7 - Existing Wastewater Collection System Upgrades / Assessment Costs
Item Cost
Sewage Pump Station Upgrades
Pump Station Infrastructure (controls, pumps, etc.) $185,000
Backup Power Generation $48,000
Engineering (12%) $28,000
Contingency (25%) $58,000
Total $319,000
Collection System Asset Condition Assessment Program
Condition Assessment of Manholes based on 78 MHs $33,000
Condition Assessment of Sewer Mains based on 1.4 kms of
infrastructure $28,000
Total $61,000
Sewer Separation Measures
Separation based on 7.3 kms of sewer @ $45,000/km $329,000
Engineering (10%) $33,000
Contingency (25%) $82,000
Total $444,000
Total Estimated Existing Collection System Upgrade and
Assessment Costs $824,000
HEJV Donkin Wastewater System Pre-Design Summary Report 15
CHAPTER 7 PROJECT IMPLEMENTATION TIMELINE
7.1 Implementation Schedule
Figure 1 provides a tentative schedule for implementation of wastewater system upgrades for Donkin,
including proposed wastewater interception and treatment infrastructure as well as upgrades to and
assessment of the existing collection system.
For the Low Risk systems such as Donkin, it is expected that implementation of proposed upgrades
will proceed on a staggered basis over the next 20 years as dictated by funding availability. As each
of these systems have the same target deadline, the prioritization will likely depend on not only the
availability of funding but also external factors. As the prioritization of the low risk systems is not
currently known, the project implementation schedule has been tentatively outlined on a generalized
basis (Year 1, Year 2, etc.) rather than with specified deadlines.
The schedule has been structured such that asset condition assessments and investigations to locate
sources of extraneous water entering the system would be carried out in Year 1. The two subsequent
years are allotted for design/construction of recommended upgrades. However, it is conceivable that
this could be completed in one year, depending on the scope of work required. It is proposed that,
during the following year, a follow-up wastewater flow metering program would be carried out to
confirm design flows for new infrastructure and gauge the effect of upgrades to the existing collection
system. The subsequent four years after the follow-up flow metering program have been allotted to
carry out design/construction of the new interception and treatment system. However, it is
conceivable that this work could be completed within three (3) years. This results in a tentative
implementation schedule that covers an eight (8) year timeline, which as noted above could be
compressed to six (6) years to align with typical funding programs for major infrastructure.
It should be noted that, although the process of pursuing the acquisition of properties and easements
required to construct the proposed wastewater upgrades is not shown on the Project Implementation
Schedule, it is recommended that the CBRM pursue these acquisitions prior to the commencement
of detailed design.
No. Project Component Period: Jan ‐ Mar Apr ‐ Jun Jul ‐ Sept Oct ‐ Dec Jan ‐ Mar Apr ‐ Jun Jul ‐ Sept Oct ‐ Dec Jan ‐ Mar Apr ‐ Jun Jul ‐ Sept Oct ‐ Dec Jan ‐ Mar Apr ‐ Jun Jul ‐ Sept Oct ‐ Dec
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
Schedule:
Cash Flow:
9 Carry out tendering, construction, commissioning and initial systems operations for proposed
wastewater treatment infrastructure $8,117,100
7 Carry out tendering, construction, commissioning and initial systems operations for proposed
wastewater interception infrastructure $549,980
8 Carry out detailed design for proposed wastewater treatment infrastructure
$294,400
5 Carry out tendering, construction and commissioning for recommended upgrades to the existing
collection system $738,600
6 Carry out detailed design for proposed wastewater interception infrastructure
$16,800
3 Carry out Sewer Separation Investigation Study to locate sources of extraneous water entering the
collection system $15,000
4 Carry out detailed design for recommended upgrades to the existing collection system based on
previous assessments $24,400
1 Carry out asset condition assessment of all manholes in the existing collection system
$33,000
2 Carry out video inspection and assessment of selected sanitary sewers in the existing collection system
$28,000
Figure 1 ‐ Project Implementation Schedule Donkin Wastewater System
Year:1234
HEJV Donkin Wastewater System Pre-Design Summary Report Appendices
APPENDIX A
Donkin Collection System Pre-Design Brief
187116 ●Final Brief ●April 2020
Environmental Risk Assessments & Preliminary
Design of Seven Future Wastewater Treatment
Systems in CBRM
Donkin Collection System Pre-Design Brief
Prepared by: HEJVPrepared for: CBRM
March 2020
March 27, 2020
275 Charlotte Street
Sydney, Nova Scotia
Canada
B1P 1C6
Tel: 902-562-9880
Fax: 902-562-9890
_________________
DONKIN COLLECTION SYSTEM FINAL SUBMISSION/ek
ED: 16/04/2020 12:45:00/PD: 16/04/2020 12:46:00
April 16, 2020
Matthew D. Viva, P.Eng.
Manager of Wastewater Operations
Cape Breton Regional Municipality
320 Esplanade, Sydney, NS B1P 7B9
Dear Mr. Viva:
RE: Environmental Risk Assessments & Preliminary Design of Seven Future
Wastewater Treatment Systems in CBRM – Donkin Collection System
Pre-Design Brief
Harbour Engineering Joint Venture (HEJV) is pleased to submit the following
Collection System Pre-Design Brief for your review and comment. This Brief
summarizes the interceptors and local sewers that will form the proposed
wastewater collection system for the community of Donkin. The collection
system will convey sewer to/from a future Wastewater Treatment Facility that
will be located northeast of Bastable Street, adjacent to Bordens Cove. The Brief
also outlines the design requirements and standards for the required collection
system infrastructure components.
We look forward to your comments on this document.
Yours very truly,
Harbour Engineering Joint Venture
Prepared by: Reviewed by:
James Sheppard, P.Eng. Darrin McLean, MBA, FEC, P.Eng.
Civil Infrastructure Engineer Senior Civil Engineer
Direct: 902-562-9880 Direct: 902-539-1330
E-Mail:jsheppard@dillon.ca E-Mail:dmclean@cbcl.ca
Project No: 187116 (Dillon) and 182402.00 (CBCL)
March 27, 2020
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief i
Contents
CHAPTER 1 Introduction & Background ........................................................................................... 1
1.1 Introduction ................................................................................................................... 1
1.2 System Background ........................................................................................................ 1
CHAPTER 2 Design Parameters & Standards .................................................................................... 3
2.1 General Overview ........................................................................................................... 3
2.2 Design Standards ............................................................................................................ 3
CHAPTER 3 Wastewater Interceptor Pre- Design ............................................................................. 5
3.1 General Overview ........................................................................................................... 5
3.2 Design Flows .................................................................................................................. 5
3.2.1 Theoretical Flow ................................................................................................. 6
3.2.2 Observed Flow .................................................................................................... 6
3.2.3 Flow Conclusions & Recommendations ............................................................... 7
3.2.4 Wet Weather Conditions Assessment ................................................................. 8
3.3 Interceptor System ......................................................................................................... 9
3.4 Combined Sewer Overflows............................................................................................ 9
3.5 Pumping Stations ........................................................................................................... 9
3.5.1 Pumping Design Capacity .................................................................................. 10
3.5.2 Safety Features ................................................................................................. 10
3.5.3 Wetwell ............................................................................................................ 11
3.5.4 Station Piping.................................................................................................... 11
3.5.5 Equipment Access ............................................................................................. 11
3.5.6 Emergency Power ............................................................................................. 11
3.5.7 Controls ............................................................................................................ 12
CHAPTER 4 Existing Collection System Upgrades ........................................................................... 13
4.1 Sewage Pump Station Upgrades ................................................................................... 13
4.2 Asset Condition Assessment Program ........................................................................... 13
4.3 Sewer Separation Measures ......................................................................................... 13
CHAPTER 5 Pipe Material Selection and Design ............................................................................. 14
5.1 Pipe Material ................................................................................................................ 14
CHAPTER 6 Land and Easement Requirements .............................................................................. 15
6.1 WWTP Site ................................................................................................................... 15
6.2 Linear Infrastructure and Access Road .......................................................................... 15
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief ii
CHAPTER 7 Site Specific Constraints ............................................................................................... 16
7.1 Construction Constraints .............................................................................................. 16
7.2 Access Requirements.................................................................................................... 16
CHAPTER 8 Opinion of Probable Costs ........................................................................................... 17
8.1 Opinion of Probable Costs – New Wastewater Collection Infrastructure ....................... 17
8.2 Opinion of Operations and Maintenance Costs ............................................................. 17
8.3 Opinion of Existing Collection System Upgrades and Assessment Costs ........................ 18
8.4 Opinion of Annual Capital Replacement Fund Contributions ......................................... 19
CHAPTER 9 References ................................................................................................................... 20
Tables
Table 2-1 Sewer Design Criteria ............................................................................................... 3
Table 2-2 Pumping Station Design Criteria ............................................................................... 4
Table 3-1 Theoretical Flow Summary ....................................................................................... 6
Table 3-2 Flow Monitoring Location Summary ......................................................................... 7
Table 3-3 Average Dry Weather and Design Flows Results ....................................................... 7
Table 3-4 Observed Flows during Rainfall Events...................................................................... 8
Table 5-1 Comparison of Pipe Materials ................................................................................. 14
Table 6-1 WWTP Land Acquisition Details .............................................................................. 15
Table 6-2 Linear Infrastructure Land Acquisition Details ......................................................... 15
Table 8-1 Annual Operations and Maintenance Costs ............................................................ 17
Table 8-2 Estimated Existing Collection System Upgrade and Assessment Costs..................... 18
Table 8-3 Estimated Annual Capital Replacement Fund Contributions.................................... 19
Appendices
Appendix A –Drawings
Appendix B – Flow Master Reports
Appendix C – Opinion of Probable Design & Construction Costs
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 1
CHAPTER 1 INTRODUCTION &BACKGROUND
1.1 Introduction
Harbour Engineering Joint Venture (HEJV) has been engaged by the Cape Breton Regional
Municipality (CBRM) to carry out Environmental Risk Assessments (ERAs) and Preliminary Design of
seven future wastewater treatment Systems in the CBRM. The future wastewater collection and
treatment systems will serve the communities of Glace Bay, Port Morien, North Sydney & Sydney
Mines, New Waterford, New Victoria, Louisbourg and Donkin, which currently have no wastewater
treatment facilities.
The preliminary design of the wastewater interceptor systems are being completed as an addition to
the existing wastewater systems in each community. In general, the proposed interceptor sewers
will convey wastewater from the existing outfalls to the proposed Wastewater Treatment Plant
(WWTP) in each location. The complexity of each system is directly related to the number of
outfalls, geographic size and topography of each community. In general, the scope of work on the
interceptor system generally includes the following:
®Determination of design wastewater flows;
®Making recommendations on the best sites for proposed wastewater treatment facilities;
®Development of the most appropriate and cost-effective configurations for wastewater
interception; and,
®Estimation of capital and operations costs for recommended wastewater components.
This document relates to the interceptors and local gravity sewers that will form the wastewater
interceptor system for the proposed WWTP in the community of Donkin. This brief outlines the
design requirements and standards for the required infrastructure components. Information
regarding the preliminary design of the proposed wastewater treatment facility for Donkin will be
provided in a separate Design Brief.
1.2 System Background
The Community of Donkin is primarily serviced by a gravity sewer system, ranging in size from 200 to
375mm in diameter. There is one lift station within the existing Donkin wastewater collection
system, located on the Donkin Highway, across the street from Civic #383. The lift station was
upgraded in 2010, to a Flygt fiberglass submersible station. There is an overflow from the station to
an adjacent brook. The station does not have backup power.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 2
The existing collection system conveys sewage to a single pipe outfall located at Borden’s
Cove/Schooner Pond. The outfall is 375mm in diameter and is concrete encased. The pipe obvert is
set at the low, low water elevation and terminates approximately 31m from the shore. A drawing of
the existing Donkin sewer system is located in Appendix A for reference.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 3
CHAPTER 2 DESIGN PARAMETERS &STANDARDS
2.1 General Overview
The development of a wastewater interceptor system for each of the communities is highly
dependent upon the selection of appropriate design parameters. HEJV has reviewed applicable
design standards and has developed the preliminary design of the interceptor sewer to meet and
exceed these industry standards.
2.2 Design Standards
The design of the interceptor system has been based on the following reference documents and
standards:
®Atlantic Canada Wastewater Guidelines Manual for Collection, Treatment, and Disposal
(ACWGM) (Environment Canada, 2006); and
®Water Environment Federation: Manual of Practice FD-4, Design of Wastewater and
Stormwater Pumping Stations.
The key design criteria that have been established for this project are presented in Table 2-1.
Table 2-1 Sewer Design Criteria
Description Unit Design Criteria Source Comments
Hydraulic Capacity l/s Location dependent HEJV Flow has been set to the Peak Rate
for the sewershed.
Material of gravity pipe PVC or Reinforced
concrete
CBRM See discussion in Chapter 5
Hydraulic design gravity Manning’s Formula ACWGM n = 0.013
Maximum spacing
between manholes
m 120 for pipes up to
and including 600 mm
and 150 for pipes over
600 mm
ACWGM
Gravity pipe minimum
design flow velocity
m/s 0.6 ACWGM
Gravity pipe maximum
flow velocity
m/s 4.5 ACWGM
Pipe crossings separation mm 450 minimum Minimum separation must also meet
Nova Scotia Environment (NSE)
requirements.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 4
Description Unit Design Criteria Source Comments
Horizontal pipe separation
gravity pipe to water main
m 3.0 ACWGM Can be laid closer if the installation
meets the criteria in Section 2.8.3.1
Gravity pipe minimum
depth of cover
m 1.5 HEJV Subject to Interferences
Gravity pipe maximum
depth of cover
m 4.5 HEJV Subject to Interferences. Increased
depth may be considered where
warranted
Table 2-2 provides a summary of the key design criteria for the Pumping Stations.
Table 2-2 Pumping Station Design Criteria
Description Unit Design Criteria Source Comments
Pump cycle time 1 hour 5 < cycle <10 WEF/
ACWGM
Number of pumps
Minimum of two. Must be
able to pump design flow
with the largest pump out
of service.
ACWGM
Three minimum for stations
with flows greater than 52
l/s.
Inlet sewer One maximum ACWGM Only a single sewer entry is
permitted to the wetwell.
Header pipe diameter mm 100 minimum ACWGM
Solids handling mm 75 (minimum)ACWGM
Smaller diameter
permissible for macerator
type pumps.
Emergency power
generation
To be provided for firm
capacity of the facility.ACWGM
Can employ overflow
options per 3.3.1. Option to
run one pump if conditions
of 3.3.5.1 are met.
Pump station wetwell
ventilation
Air
changes/
hour
30 (Wetwell)
12 (Valve Chamber)ACWGM
Based on intermittent
activation when operating
in the wet well.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 5
CHAPTER 3 WASTEWATER INTERCEPTOR PRE-DESIGN
3.1 General Overview
A drawing of the existing Donkin collection system has been included in Appendix A. The drawing
was created using background data collected from various sources to depict the layout of the
existing gravity network.
The proposed wastewater interceptor system for Donkin will include a gravity sewer that will
redirect flow from the existing outfall to a lift station. The lift station will convey flow to the
proposed Waste Water Treatment Plant (WWTP) site approximately 120 metres away. A gravity
outlet sewer will be required to direct the treated flow from the proposed WWTP, back to the
original outfall.
For this Pre-Design Brief, HEJV has compiled a preliminary plan and profile drawing of the proposed
linear infrastructure. The locations of the required linear infrastructure, outfall and WWTP have also
been illustrated on the drawings and are included in Appendix A.
3.2 Design Flows
HEJV completed a review of the theoretical and observed sanitary flows for the Donkin sewershed.
The purpose of the assessment was to estimate average and design flows for the environmental risk
assessment (ERA) and the preliminary design of the future WWTP and interception system.
It is anticipated that the future WWTP for the community will be a stabilization pond with an
engineered wetland. Since the flow is being conveyed to a stabilization pond, it makes sense to
intercept all of the peak flow and divert it to the WWTP. The stabilization pond should be sized for
the average daily flow in the community regardless of the intercepted flow rate. Intercepting the
peak flow will end raw sewage being directly discharged at the existing Donkin Outfall. The
stabilization pond with an engineered wet land, will offer some level of treatment to all flows
directed to the WWTP versus setting an overflow before the WWTP based on an ADWF multiplier.
Periods of higher flows, will cause the retention time in the pond to decrease, however, discharged
flows would have been detained in the pond for some time (partially treated) before release.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 6
3.2.1 Theoretical Flow
Theoretical flow was calculated based on design factors contained in the ACWGM. To estimate
population, the number of private dwellings were estimated then multiplied by an average
household size. An average value of 2.2 persons per household was used based on the average
household size found in the 2016 Statistics Canada information for Cape Breton. The number of
apartments, nursing homes, townhouses, and other residential buildings were estimated and
considered in the population estimate. Population estimates are shown in Table 3-1. The peak
design flow was calculated using the following equation (1):
ܳ(݀)=ܲݍܯ
86.4 +ܫܣ (1)
Where:
Q(d) = Peak domesƟc sewage flow (l/s)
P = PopulaƟon (in thousands)
q =Average daily per capita domesƟc flow (l/day per capita)
M = Peaking factor (Harman Method)
I = unit of extraneous flow (l/s)
A = Subcatchment area (hectares)
ACWGM recommends an average daily domestic sanitary flow of 340 l/day per person for private
residential dwellings. The unit of extraneous flow was assumed to be approximately 0.21 l/s/ha
based on typical ranges outlined in ACWGM. The contributing sewershed was estimated to be 52
ha. The peaking factor used in Equation 1 was determined using the Harman Formula (2) shown
below:
Harman Formula
ܯ =1+14
4+ܲ.ହ (2)
The estimated average dry weather flow (ADWF) and peak design flows based on the ACWGM
methods discussed above are presented in Table 3-1.
Table 3-1 Theoretical Flow Summary
Estimated Area (ha)Estimated Population1 ADWF2 (l/s)Peak Design Flow3 (l/s)
58 540 2.12 20.87
1 2016 Cape Breton Census from StaƟsƟcs Canada
2Based on average daily sewer flows of 340 L/day/person (ACWGM 2006)
3EsƟmated using ACWGM equaƟon for peak domesƟc sewage flows (including extraneous flows and peaking factor)
3.2.2 Observed Flow
One flow monitoring staƟon was installed in Donkin, near the end of Bastable Lane. The selected
locaƟon is part of the ouƞall system that receives all of the Donkin sewer shed flow. Upon review of
the flow data, a sharp increase in flows was observed shortly aŌer deployment (February 20th –
March 13th). The average flow rate during the period was in the order of 15 L/s for this Ɵmeframe.
The data also suggested that there was a conƟnual base flow of 6 l/s. In response, HEJV moved the
flow monitor to another suitable manhole in the Donkin ouƞall system to verify the data.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 7
Immediately aŌer re-deployment, flow observaƟons seemed to return to the lower values reported
before the Ɵme frame in quesƟon. This suggests that the logger was briefly over-esƟmaƟng flows in
its original locaƟon. For this reason, the three week period has been removed from the dataset
prior to compleƟng our analysis. A summary of the flow meter locaƟon and monitoring duraƟon is
provided in Table 3- 2.
Table 3-2 Flow Monitoring Location Summary
Northing Easting Monitoring Start-End Dates Days of Data
5117614.066 4626479.151 February 15-April 2, 2018 47
Analysis for observed dry weather flows were completed using the United States Environmental
Protection Agency’s (EPA) Sanitary Sewer Overflow Analysis and Planning (SSOAP) toolbox. The
SSOAP toolbox is a suite of computer software tools used for capacity analysis and condition
assessments of sanitary sewer systems.
Flow and rainfall data were input into the SSOAP program, along with sewershed data. To determine
average dry weather flow (ADWF), days that were influenced by rainfall were deleted. This was done
in the SSOAP model by removing data from days that had any rain within the last 24 hours, more
than 5 mm in the previous 48 hours, and more than 5 mm per day additional in the subsequent days
(e.g. 10 mm in the last 3 days). Again, the subset of flow data without the three week period noted
in earlier in this section was used in the SSOAP program.
The calculated ADWF estimates are based on the subset of flow data without the three week period
previously described in this section, evaluated using the SSOAP program are presented in Table 3-3,
along with average and peak flow from raw monitored data.
Table 3-3 Average Dry Weather and Design Flows Results
ADWF From SSOAP Model (l/s)Average Daily Observed Flow (l/s)Peak Flow
(l/s)
2.3 7.99 36.81
3.2.3 Flow Conclusions & Recommendations
HEJV recommends that the flow rate for the design of the proposed interceptor sewer be designed
to avoid excessive overflow events. Based on the data collected by HEJV, a flow of 18l/s has been
recommended as the peak flow to be conveyed to the proposed WWTP. This flow equates to
7.75X’s ADWF. This flow is also illustrated below graphically to show the proposed peak flow against
flow data collected by HEJV.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 8
3.2.4 Wet Weather Conditions Assessment
To evaluate performance of the proposed interception system during wet weather conditions,
metered flows during rainfall events have also been considered. The results of the wet weather
flow assessment at the metered location is presented in Table 3-4. The calculated flows were
compared to the recommended design flow to indicate if sewer overflow/surcharge conditions
would be anticipated.
Table 3-4 Observed Flows during Rainfall Events
Monitoring Station
Minor Rainfall Event
(10-25 mm Daily Rainfall)
# of Events Daily Average
Flow (l/s)
Expected Overflow1
(Y/N)
Donkin 5 8-21 Y
1 Overflow expected when observed flow exceeds design flow
The results in Table 3-4 suggest that the interception system will be able to accommodate the wet
weather flows that were monitored during the flow gauging exercise.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 9
3.3 Interceptor System
The proposed interceptor system for the Donkin WWTP is presented on the plan and profile drawing
attached in Appendix A. The proposed interceptor system is made up of gravity connections to the
existing collection system, a lift station, a forcemain to the wastewater treatment plant, and a
gravity sewer to the outfall.
The first step in laying out the interceptor sewer route was to determine the location of the future
WWTP that will serve the community of Donkin. To accomplish this, the type of treatment process
needed to be considered, along with the availability of land.
At this time, HEJV has proposed an aerated lagoon for the proposed Donkin WWTP, as it offers an
appropriate level of treatment at the lowest capital and operation cost for CBRM. HEJV reviewed
the community of Donkin and surrounding areas for possible locations for the WWTP site. The
review led to a location that consisted of PID’s 15494248 (privately owned by Simon Edward Baxter)
and 15277353 (owned by Cape Breton Regional Municipality). This location provides a remote
distance away from residential development. In this case, a remote distance is defined as being at
least 150 m from isolated human habitation as required by ACWGM. The location also provides
adequate distance as defined by ACWGM away from neighboring property boundaries. The
proposed location of the WWTP has been shown on the existing sewer system drawing included in
Appendix A.
With the WWTP location selected, HEJV laid out the interceptor sewer. The major elements of the
interceptor system include:
®A duplex submersible pump station that will be located on PID 15064694 near the end of
Bastable Street. This pump station intercepts flow from the existing 250mm diameter sewer,
and the existing 375mm diameter sewer that connects to the outfall. The pump station will
convey flow northward to the proposed WWTP via a 150mm forcemain that is
approximately 120m in length.
®Treated flow will be conveyed back to the existing outfall via a 375 mm diameter outlet
gravity sewer for a length of approximately 75 metres.
Flow Master reports for the proposed linear infrastructure, illustrated on Sheet 1 in Appendix A,
have been included in Appendix B.
3.4 Combined Sewer Overflows
A combined sewer overflow (CSO) should be utilized in the proposed interceptor system where
flows directed to a pump station exceed the interception design rate defined in Section 3.2.3. For
this system, it is recommended to integrate an overflow into the lift station instead of a separate
CSO due to the design flows, and future population projections.
3.5 Pumping Stations
As discussed, one (1) new pump station will be required in the proposed Donkin interceptor system
to convey wastewater to the proposed WWTP. The pump station should be equipped with non-clog
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 10
submersible pumps with an underground wetwell. For this small duplex station, due to economics, a
buried valve chamber to host the mechanical piping, valves, and flowmeter will be provided. All
electrical and controls will be kept in the adjacent WWTP.
A hydraulic analysis should be completed on the forcemain to determine if surge valves are
warranted, in addition to the VFDs that are discussed in Section 3.5.1. If required, the valves should
be installed prior to the forcemain exiting the pump station to protect the pipe against unwanted
surge forces. Standard pump station schematics have been presented in Appendix A for illustrative
purposes.
3.5.1 Pumping Design Capacity
The station will be designed to pump the intercepted flows defined in Section 3.2.3 with the largest
pump out of service as per ACWGM. All pumps will be supplied and operated with variable
frequency drives (VFD). A VFD will provide the following benefits to the pumping system:
®Energy savings by operating the pump at its best efficiency point;
®Prevent motor overload;
®Energy savings by eliminating the surge at pump start up; and,
®Water hammer mitigation.
3.5.1.1 LS1
The pump station will be a duplex station with 150 mm diameter internal piping, and a 2.4 m
diameter pre-cast wet well. The station will have one duty and one standby pump which each will
each have a capacity of 20 l/s, with a TDH of 12.7 m.
3.5.1.2 PUMP STATION SUMMARY
Table 3-5 Pump Station Summary
Lift
Station
Duty/
Standby
Pumps
ADWF
(l/s)
Maximum
Design
Flow (l/s)
Pump
Capacity
(l/s, duty
pump(s))
Station
Piping
Diameter
(mm)
TDH (m)
at
Maximum
Design
Flow
Velocity
in
Forcemain
(duty
pump(s)
running)
Approximate
Power Per
Pump (Kw)
LS1 1/1 4.2 18.0 20.0 150 12.7 1.07 3.4
3.5.2 Safety Features
The station should report alarm conditions to the CBRM SCADA network. The station should also
incorporate external visual alarms to notify those outside of an alarm condition. External audible
alarms should not be used as the station is in a populated area and disturbance to the local
community should be kept to a minimum.
All access hatches should include safety grating similar to Safe-Hatch by Flygt.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 11
3.5.3 Wetwell
The wetwell should be constructed with a benched floor to promote self-cleansing and to minimize
any potential dead spots.
The size of the wetwell should be based on factors such as the volume required for pump cycling,
dimensional requirements to avoid turbulence problems, the vertical separation between pump
control points, the inlet sewer elevation, capacity required between alarm levels, overflow
elevations, the number of pumps and the required horizontal spacing between pumps.
The operating wetwell volume for the pump station should be based on alternating pump starts
between available pumps while reducing retention times to avoid resultant odours from septic
conditions.
At this time HEJV recommends a precast unit for the station. Based on the conditions discussed
above, the sizing for each of the wetwells is presented below.
Table 3-6 Wetwell Sizing Summary
Pumping Station Size and Shape
(m)
Depth
(m)
LS-ND1 2.4 Circular 4.3
3.5.4 Station Piping
Pump station piping should be ductile iron class 350 with coal tar epoxy lining or stainless steel with
diameters as indicated in Table 3-5. Threaded flanges or Victaulic couplings should be used for
ductile iron pipe joints, fittings and connections within the station. Pressed or rolled vanstone neck
flanges should be used for stainless steel pipe joints, fittings and connections. Piping layout should
be designed to provide minimum friction loss and to provide easy access to all valving,
instrumentation and equipment for the operators.
A common flow meter on the discharge header should be provided to monitor flows.
3.5.5 Equipment Access
Pump installation and removal should be achieved using a lifting davit and electric hoist that would
access the pumps through hatches located above the pumps. Due to maintenance issues associated
with exterior davit sockets and portable davits, a weather-tight enclosure should be provided to
protect the davit when it is not in use, or provisions should be made to house it in the adjacent
WWTP building
All valves and flow monitoring equipment should be located in a common below grade valve
chamber. This valve chamber should be weather-tight, and would be complete with a drain to
remove any intruding water.
3.5.6 Emergency Power
The station shoulf be equipped with a backup generator sized to provide power to all equipment,
and accessories during power interruptions. An automatic power transfer switch should transfer the
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 12
station’s power supply to the generator during a power disruption and should return to normal
operation when power has been restored. The generator should be supplied with noise suppression
equipment to limit disruption to existing neighbours.
It is assumed at this time that backup power will be shared with the adjacent WWTP.
3.5.7 Controls
It is assumed that a local control panel for the station will be located inside the adjacent WWTP. The
local control panel would be a custom panel designed to be integrated into the CBRM SCADA
network. The panel should provide a Hand/Off/Auto control selector to allow for manual control of
the station. The control system should report remotely to CBRM’s SCADA system including alarm
conditions.
Control instrumentation and equipment should include the following:
®Level sensors/transmitters in the wetwell;
®Flow meter/transmitter on the discharge forcemain(s);
®Pressure transmitter;
®Surge valve position indication (if required);
®Level alarms;
®Pump fault; and,
®Overflow level measurement (either side of weir plate).
The level in the wetwell utilizing ultrasonic level instruments should control the operation of the
pumps. A second ultrasonic level instrument should be used to record overflow events. Auxiliary
floats will provide high and low level alarms as well as back-up control in the event of a failure in the
ultrasonic equipment.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 13
CHAPTER 4 EXISTING COLLECTION SYSTEM UPGRADES
4.1 Sewage Pump Station Upgrades
HEJV has reviewed the existing Donkin Collection System for potential upgrades to the existing
sewage pumping stations. There is currently one pump station in the community of Donkin, which
was upgraded in 2010. The Donkin WWTP has been classified as a low priority system and has an
implementation deadline of 2040. Considering that 2040 is 21 years in the future, plans should be
made to upgrade the existing pump station as part of the interception work to be completed in the
community. Due to age, the necessity to upgrade the existing station may occur prior to the
implementation of the interceptor sewer project. Therefore, the condition of the station should be
verified at the time of detailed design to determine if an upgrade is required.
4.2 Asset Condition Assessment Program
To get a better sense of the condition of the existing Donkin sewage collection system, HEJV
recommends completing a sewage collection system asset condition assessment program in the
community. The program would carry out an investigation involving two components:
®Visual inspection and assessment of all manholes in the collection system
®Video inspection of 20% of all sewers in the system
The program should be completed with the issuance of a Collection System Asset Condition
Assessment Report that would summarize the condition of the various assets inspected and include
opinions of probable costs for required upgrades.
4.3 Sewer Separation Measures
CBRM should consider completing a sewer separation investigation program for Donkin. The
program would review catch basins that are currently connected or possibly connected to existing
sanitary sewers. The program should also include the costing of the installation of new storm
sewers to disconnect catch basins from the existing sanitary sewer.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 14
CHAPTER 5 PIPE MATERIAL SELECTION AND DESIGN
5.1 Pipe Material
Four pipe materials (Ductile Iron, HDPE, PVC, and Reinforced Concrete) were considered for this
project and were evaluated against various factors. Ductile Iron (DI), HDPE and PVC were reviewed
for a suitable forcemain material for the project. PVC and Reinforced Concrete were reviewed
against each other for a suitable gravity pipe material. A summary of the advantages and
disadvantages of the different materials is presented in Table 5-1.
Table 5-1 Comparison of Pipe Materials
Pipe
Material Advantages Disadvantages
Ductile
Iron
·Is forgiving with regard to problems
caused by improper bedding
·Thinnest wall, greatest strength
·Standard testing method
·CBRM staff and contractors are familiar
with installation of DI forcemains
·Pipe and fittings are susceptible to corrosion
·High weight
·Installation cost is high
HDPE
·Excellent corrosion resistance of pipe
·Long laying lengths (where practical)
·Relatively easy to handle
·Requires good bedding
·Requires butt fusing
·Careful handling is required due to abrasion
·Long distances of open trench
·Not designed for vacuum conditions
·Installation cost is high if long lay lengths are
not possible
PVC
·CBRM standard
·Excellent corrosion resistance of pipe
·Standard testing method
·Light weight
·High impact strength
·CBRM staff and contractors are familiar
with installation of PVC forcemains
·Cost competitive
·Requires good bedding
·Must be handled carefully in freezing
conditions
Reinforced
Concrete
·High strength
·Standard testing method
·CBRM staff and contractors are familiar
with installation
·Heavy – harder to handle
·Susceptible to attached by H2S and acids when
not coated
·Requires careful installation to avoid cracking
·Short laying lengths
Based on the above comparison, HEJV recommends that the gravity sewer and forcemain piping for
the Donkin interceptor sewer be PVC.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 15
CHAPTER 6 LAND AND EASEMENT REQUIREMENTS
HEJV has reviewed the requirements for land acquisition and easements. A portion of the proposed
interceptor system and WWTP will be constructed within CBRM owned land parcels. However,
portions of the treatment plant are shown on private property. In addition an access road and an
outlet from the WWTP would need to be constructed on privately owned lands.
6.1 WWTP Site
As discussed in Section 3.3, the WWTP will be located on a parcel of land privately owned by Simon
Edward Baxter. HEJV recommends purchasing the entire lot, due to the size of the development and
the permanence of the development. Presented below in Table 6-1 are some of the pertinent
details of the parcel of land required to build the WWTP.
Table 6-1 WWTP Land Acquisition Details
PID Property Owner Assessed Value Description Purchase Entire Lot
(Y/N)
15494248 Simon Edward
Baxter $7,600 WWTP Site Y
6.2 Linear Infrastructure and Access Road
The installation of the linear infrastructure and access road will require an easement on two parcels
land privately owned by Simon Edward Baxter. The remaining linear infrastructure will be installed
within CBRM owned land and the parcel of land that HEJV has recommended for purchase in Table
6-2. Details on the required easement area are as follows:
Table 6-2 Linear Infrastructure Land Acquisition Details
PID Property Owner Assessed
Value Description Size Required
Purchase
Entire Lot
(Y/N)
15064694 Simon Edward
Baxter
$4,900 Access Road
Lift Station
900m2 N
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 16
CHAPTER 7 SITE SPECIFIC CONSTRAINTS
During the preliminary design of the interceptor system, HEJV has reviewed the site for the pipe
routing for potential constraints. HEJV reviewed construction constraints, environmental constraints
and access requirements for the proposed interceptor infrastructure. The next sections of the
Design Brief briefly touch on items that were found during HEJV’s review.
7.1 Construction Constraints
HEJV has reviewed the preliminary design of the interceptor system from a construction constraints
perspective.
A large ditch exists in the area of the proposed access road near the end of Bastable Street.
Depending on the time of year that construction takes place; a water management system may
need to be implemented in order to construct the access road.
7.2 Access Requirements
The WWTP location is somewhat remote and will require an access road to be constructed along
with an entrance gate for security purposes. Access road requirements for the WWTP site will be
further detailed in the Donkin WWTP Pre-Design Brief.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 17
CHAPTER 8 OPINION OF PROBABLE COSTS
8.1 Opinion of Probable Costs – New Wastewater Collection Infrastructure
An opinion of Probable Design & Construction Costs for new wastewater collection system
infrastructure has been completed for the project. A detailed breakdown of the estimate has been
provided in Appendix C. The estimate is made up of the linear infrastructure design, lift station
design, construction costs and associated land acquisition costs required to collect and convey the
sanitary sewer in Donkin to the proposed WWTP. For land acquisition costs, HEJV has used a ratio of
the amount of land that is affected by the required easement/property acquisition multiplied by the
assessed value of the entire lot. The Opinion of Probable Design and Construction Costs for the
interceptor sewer for Donkin is $566,180. This is considered to be a Class ‘C’ cost estimate, accurate
to within plus or minus 30%.
8.2 Opinion of Operations and Maintenance Costs
HEJV completed an Opinion of Operational Costs for the interceptor system using data provided by
CBRM for typical annual operating costs of their existing submersible lift stations, typical employee
salaries, Nova Scotia Power rates, and experience from similar stations for general maintenance. The
opinion of operational costing includes general lift station maintenance costs, general linear
maintenance costs, employee operation and maintenance costs, electrical operational costs, and
backup generator operation and maintenance costs. A breakdown of costs has provided in
Table 8-1.
Table 8-1 Annual Operations and Maintenance Costs
The general station maintenance cost presented above includes pump repairs (impellers, bearings,
and seals), electrical repairs and instrumentation repairs and servicing.
The general linear maintenance cost for the interceptor system has been estimated to be $500 per
year in 2019 dollars. This includes flushing, inspection, and refurbishment of structures along the
linear portion of the collection system.
Item Costs
General Lift Station Maintenance Cost $2,500/yr
General Linear Maintenance Cost $500/yr
Employee O&M Cost $4,000/yr
Electrical Operational Cost $1,000/yr
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 18
Employee O&M costs were averaged from data provided by CBRM. It was determined that staffing
to maintain their existing lift stations requires an average of 100 hours of effort per submersible lift
station per year.
For the electrical operation basic electrical loads for instrumentation were assumed. Electrical
demand from the pumping system was determined based on the yearly average flow of the station.
8.3 Opinion of Existing Collection System Upgrades and Assessment Costs
Opinions of probable cost have been provided to complete the work that was discussed in Chapter
4. For sewage pumping stations, the opinion of probable cost includes a full retrofit of the existing
station including new pumps, controls and backup power generation. The need to upgrade the
station should be verified at detailed design, as discussed in Chapter 4. Lift station upgrade costs are
presented in Table 8-2. HEJV has provided an allowance of 12% on the cost of construction for
engineering and 25% for contingency allowance.
An opinion of probable costs has been provided for the collection system asset condition
assessment program described in Chapter 4. These costs include the video inspection and flushing of
20% of the existing sanitary sewer network, visual inspection of manholes, traffic control and the
preparation of a collection system asset condition assessment report.
For sewer separation measures, budgetary pricing has been calculated by reviewing recent costs of
sewer separation measures in CBRM involving installation of new storm sewers to remove
extraneous flow from existing sanitary sewers. These costs have been translated into a cost per
lineal meter of sewer main. This unit rate was then applied to the overall collection system. The cost
also includes an allowance of 10% on the cost of construction for engineering and 25% for
contingency allowance.
Estimates of costs for upgrades to and assessment of the existing collection system as outlined in
Table 8-1 are considered to be Class ‘D’, accurate to within plus or minus 45%.
Table 8-2 Estimated Existing Collection System Upgrade and Assessment Costs
Item Cost
Sewage Pump Station Upgrades
Pump Station Infrastructure (controls, pumps, etc.)$185,000
Backup Power Generation $48,000
Engineering (12%)$28,000
Contingency (25%)$58,000
Total $319,000
Collection System Asset Condition Assessment Program
Condition Assessment of Manholes based on 78 MH’s $33,000
Condition Assessment of Sewer Mains based on 1.4km’s of infrastructure $28,000
Total $61,000
Sewer Separation Measures
Separation based on 7.3km’s of sewer @ $45,000/km $329,000
Engineering (10%)$33,000
Contingency (25%)$82,000
Total $444,000
Total Estimated Existing Collection System Upgrade and Assessment Costs $824,000
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 19
8.4 Opinion of Annual Capital Replacement Fund Contributions
The CBRM wishes to create a Capital Replacement Fund to which annual contributions would be
made to prepare for replacement of the assets at the end of their useful life. The calculation of
annual contributions to this fund involves consideration of such factors as the type of asset, the
asset value, the expected useful life of the asset, and the corresponding annual depreciation rate for
the asset. In consideration of these factors,Table 8-3 provides an estimation of the annual
contributions to a capital replacement fund for the proposed new wastewater collection and
interception infrastructure.
Table 8-3 Estimated Annual Capital Replacement Fund Contributions
Description of Asset Asset Value
Asset Useful
Life
Expectancy
(Years)
Annual
Depreciation
Rate (%)
Annual Capital
Replacement
Fund Contribution
Linear Assets (Piping, Manholes and Other)$109,080 75 1.3%$1,418
Pump Station Structures (Concrete
Chambers, etc.)$136,215 50 2.0%$2,724
Pump Station Equipment (Mechanical /
Electrical)$166,485 20 5.0%$8,324
Subtotal $411,780 --$12,466
Contingency Allowance (Subtotal x 25%):$3,117
Engineering (Subtotal x 10%):$1,247
Opinion of Probable Annual Capital Replacement Fund Contribution:$16,830
Note:
Annual contribuƟons do not account for annual inflaƟon.
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 20
CHAPTER 9 REFERENCES
Environment Canada (2006) –Atlantic Canada Wastewater Gidelines Manual for Collection,
Treatment and Disposal.
Harbour Engineering Inc. (2011).Cape Breton Regional Municipality Wastewater Strategy 2009.
Nova Scotia Environment (2018).Environment Act.
Nova Scotia Utility and Review Board (2013).Water Utility Accounting and Reporting Handbook.
UMA Engineering Ltd. (1994). Industrial Cape Breton Wastewater Characterization Programme –
Phase II.
Water Environment Federation (2009),Design of Wastewater and Stormwater Pumping Stations
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 21
APPENDIX A
Drawings
PROPOSED LOCATION FOR
THE DONKIN WWTP
EXISTING OUTFALL D#1
1
ENVIRONMENTAL RISK ASSESSMENTS
& PRELIMINARY DESIGN
JRS
JRS TAB
TAB 18-7116
1:3000
FEBRUARY 2020
HA
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A
B
C
ISSUED FOR REVIEW
ISSUED FOR DRAFT DESIGN BRIEF
ISSUED FOR FINAL DESIGN BRIEF
02/27/18
10/15/18
02/28/20
JRS
JRS
JRS DONKIN EXISTING COLLECTION SYSTEM
DATE
DESIGN
DRAWN
PROJECT NO.
SHEET NO.
No.DATE BYISSUED FOR
written permission from Harbour Engineering Joint Venture.
than those intended at the time of its preparation without prior
Do not scale dimensions from drawing.
Report any discrepancies to Harbour Engineering Joint Venture.
Verify elevations and/or dimensions on drawing prior to use.
Conditions of Use
REVIEWED BY
CHECKED BY
Do not modify drawing, re-use it, or use it for purposes other
SCALEj o i n t v e n t u r e
MACLE
A
N
S
T
CENTRE AVE
BA
S
T
A
B
L
E
S
T
EXISTING OUTFALL (D#1)
(CBRM)15494255
(CBRM)
15495021
(GLEN MUNROE
RUTHANNE
MUNROE)
15064694
(SIMON EDWARD
BAXTER)
PROPOSED 375Ø GRAVITY SEWER
OUTLINE OF PROPERTY
REQUIRING AN EASEMENT
OUTLINE OF PROPERTY
REQUIRING ACQUISITION
PROPOSED 150Ø FORCEMAIN
PROPOSED
WWTP SITE
15494248
(SIMON EDWARD
BAXTER)
15277353
L.S.#1
2
ENVIRONMENTAL RISK ASSESSMENTS & PRELIMINARY DESIGN
OF 7 FUTURE WASTEWATER TREATMENT SYSTEMS IN CBRM
JRS
JRS TAB
TAB 18-7116
AS NOTED
FEBRUARY 2020
HE
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A
B
ISSUED FOR DRAFT DESIGN BRIEF
ISSUED FOR FINAL DESIGN BRIEF
10/15/18
02/28/20
JRS
JRS
DONKIN INTERCEPTOR
PLAN/PROFILE
PLAN
1:2500
PROFILE
HOR:1:2500\VERT:1:500
DATE
DESIGN
DRAWN
PROJECT NO.
SHEET NO.
No.DATE BYISSUED FOR
written permission from Harbour Engineering Joint Venture.
than those intended at the time of its preparation without prior
Do not scale dimensions from drawing.
Report any discrepancies to Harbour Engineering Joint Venture.
Verify elevations and/or dimensions on drawing prior to use.
Conditions of Use
REVIEWED BY
CHECKED BY
Do not modify drawing, re-use it, or use it for purposes other
SCALEj o i n t v e n t u r e
1
P01
___
1
P01
___
FORCEMAIN
DRAIN PIPE
SUBMERSIBLE PUMP
(TYP.2)
CHECK VALVE
PLUG VALVE
FLOW METER
PLUG VALVE
CHECK VALVE PLUG VALVE
INLET BAFFLE
IN
L
E
T
DRAIN PIPE
DRAIN PIPE
OVERFLOW PIPE
PUMP GUIDE RAILS
DISCHARGE PIPE
SUPPORTS
PUMP LIFTING CHAIN TO EXTEND AND
ATTACH TO CHAMBER LID (TYP.3)
WET WELL BENCHING
CONCRETE
MUD SLAB
CLEAR STONE
BEDDING (TYP.)
PRECAST CONCRETE BASE, RISERS AND COVER
(TYP.)
HORIZONTAL LEVEL
REGULATOR HANGER
SUBMERSIBLE PUMP
PUMP FLOAT (TYP.)
PUMP CABLE SUPPORT
ULTRASONIC LEVEL
TRANSMITTER
C/W STAINLESS STEEL
MOUNTING BRACKET
CHECK VALVE
DRAIN LINE
FROM VALVE
CHAMBER
10
0
2% SLOPE2% SLOPE
NOTE: INLET BAFFLE NOT SHOWN FOR CLARIFY
INLET
OVERFLOW
j o i n t v e n t u r e
NTS
DATE
DESIGN
DRAWN
PROJECT NO.
SHEET NO.
No.DATE BYISSUED FOR
written permission from Harbour Engineering Joint Venture.
than those intended at the time of its preparation without prior
Do not scale dimensions from drawing.
Report any discrepancies to Harbour Engineering Joint Venture.
Verify elevations and/or dimensions on drawing prior to use.
Conditions of Use
REVIEWED BY
CHECKED BY
Do not modify drawing, re-use it, or use it for purposes other
SCALE
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18-7116ENVIRONMENTAL RISK ASSESSMENTS & PRELIMINARY DESIGN OF 7
FUTURE WASTEWATER TREATMENT SYSTEMS IN CBRM
FEBRUARY 2020
MSR JRS
P01
MSR JRS
PLAN AND SECTION
DONKIN DUPLEX PUMP STATION
WET WELL PLAN SECTION 1
0 ISSUED FOR DRAFT DESIGN BRIEF 02/28/2020 JRS
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 22
APPENDIX B
Flow Master Reports
Harbour Engineering Joint Venture Donkin Collection System Pre-Design Brief 23
APPENDIX C
Opinion of Probable Design & Construction
Costs
OPINION OF PROBABLE
COST, CLASS 'C'
Preliminary Collection Project Manager:D. McLean
and Interception Infrastructure Costs Only Est. by: J. Sheppard Checked by: D. McLean
Donkin, NS PROJECT No.:187116 (Dillon)
182402.00 (CBCL)
UPDATED:April 16, 2020
NUMBER UNIT
Linear Infrastructure $108,480.00
250 mm Diameter PVC Gravity Sewer 10 m $330.00 $3,300.00
375 mm Diameter PVC Gravity Sewer 85 m $360.00 $30,600.00
150 mm Diameter HDPE Forcemain 125 m $300.00 $37,500.00
Precast Manhole (1200mm dia.)3 each $5,500.00 $16,500.00
Connection to Existing Main (typ)2 each $8,000.00 $16,000.00
Closed Circuit Televsion Inspection 10 m $8.00 $80.00
Trench Excavation - Rock 50 m3 $60.00 $3,000.00
Trench Excavation - Unsuitable Material 50 m3 $10.00 $500.00
Replacement of Unsuitable with Site Material 25 m3 $10.00 $250.00
Replacement of Unsuitable with Pit Run Gravel 25 m3 $30.00 $750.00
LS#1 $302,700.00
Pump Station 1 l.s.$250,000.00 $250,000.00
Site Work 1 l.s.$50,000.00 $50,000.00
Mass Excavation - Rock 30 m3 $60.00 $1,800.00
MassExcavation - Unsuitable Material 30 m3 $10.00 $300.00
Replacement of Unsuitable with Site Material 15 m3 $10.00 $150.00
Replacement of Unsuitable with Pit Run Gravel 15 m3 $30.00 $450.00
SUBTOTAL (Construction Cost)$411,180.00
Contingency Allowance (Subtotal x 25 %)$103,000.00
Engineering (Subtotal x 10 %)$42,000.00
Land Acquisition $10,000.00
OPINION OF PROBABLE COST (Including Contingency)$566,180.00
UNIT COSTITEM DESCRIPTION
THIS OPINION OF PROBABLE COSTS IS PRESENTED ON THE BASIS OF EXPERIENCE, QUALIFICATIONS, AND BEST JUDGEMENT. IT HAS BEEN PREPARED IN
ACCORDANCE WITH ACCEPTABLE PRINCIPLES AND PRACTICIES, MARKET TRENDS, NON-COMPETITIVE BIDDING SITUATIONS, UNFORSEEN LABOUR AND
MATERIAL ADJUSTMENTS AND THE LIKE ARE BEYOND THE CONTROL OF HEJV. AS SUCH WE CANNOT WARRANT OR GUARANTEE THAT ACTUAL COSTS WILL
NOT VARY FROM THE OPINION PROVIDED.
PREPARED FOR:
Cape Breton
Regional Municipality
EXTENDED TOTALS QUANTITY TOTAL
March 27, 2020
HEJV Donkin Wastewater System Pre-Design Summary Report Appendices
APPENDIX B
Donkin Treatment System
Pre-Design Brief
182402.00 ● Final Brief ● April 2020
Environmental Risk Assessments & Preliminary
Design of Seven Future Wastewater Treatment
Systems in CBRM
Donkin Wastewater Treatment Plant
Preliminary Design Brief
Prepared by:Prepared for:
March 2020
Final April 20, 2020 Darrin McLean Mike Abbott
Dave McKenna
Laura Jenkins
Draft for Review Darrin McLean Mike Abbott
Dave McKenna
Laura Jenkins
Issue or Revision Date Issued By: Reviewed By: Prepared By:
This document was prepared for the party indicated
herein. The material and information in the
document reflects HEJV’s opinion and best
judgment based on the information available at the
time of preparation. Any use of this document or
reliance on its content by third parties is the
responsibility of the third party. HEJV accepts no
responsibility for any damages suffered as a result
of third party use of this document.
182402.00
March 27, 2020
182402 RE 001 FINAL WWTP PREDESIGN DONKIN APR-20 .DOCX
ED: 20/04/2020 12:20:00/PD: 20/04/2020 12:20:00
275 Charlotte Street
Sydney, Nova Scotia
Canada B1P 1C6
Tel: 902-562-9880
Fax: 902-562-9890
April 20, 2020
Matt Viva, P.Eng.
Manager Wastewater Operations
Cape Breton Regional Municipality (CBRM)
320 Esplanade
Sydney, NS B1P 7B9
Dear Mr. Viva:
RE: Donkin Wastewater Treatment Plant Preliminary Design
Enclosed, please find a copy of the Preliminary Design Brief for the Donkin
Wastewater Treatment Plant (WWTP).
The report presents an evaluation of treatment process alternatives for the
Donkin WWTP, and a preliminary design based on the recommended Aerated
Lagoon treatment process.
If you have any questions or require clarification on the content presented in
the attached report, please do not hesitate to contact us.
Yours very truly,
Harbour Engineering Joint Venture
Prepared by: Reviewed by:
Laura Jenkins, P.Eng Mike Abbott, P.Eng., M.Eng.
Process Engineer Manager Process Engineering
Direct: 902-421-7241 (Ext. 2510)
E-Mail: ljenkins@cbcl.ca
Reviewed by:
Dave McKenna, P.Eng., M.Eng.
Associate / Technical Service Lead
Project No: 182402.00 (CBCL Limited)
187116.00 (Dillon Consulting Limited)
March 27, 2020
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design i
Contents
CHAPTER 1 Introduction .......................................................................................................... 3
1.1 Introduction .................................................................................................................. 3
1.2 Background ................................................................................................................... 3
1.3 Objectives ..................................................................................................................... 3
CHAPTER 2 Existing Conditions ................................................................................................ 4
2.1 Description of Existing Infrastructure ........................................................................... 4
2.2 Flow Characterization ................................................................................................... 4
2.3 Wastewater Quality Characteristics ............................................................................. 5
2.4 Wastewater Loading Analysis ....................................................................................... 6
CHAPTER 3 Basis of Design ...................................................................................................... 8
3.1 Service Area Population ................................................................................................ 8
3.2 Design Flows and Loads ................................................................................................ 8
3.3 Effluent Requirements .................................................................................................. 9
3.4 Design Loads ................................................................................................................. 9
CHAPTER 4 Treatment Process Alternatives ........................................................................... 11
4.1 Preliminary and Treatment ......................................................................................... 11
4.2 Secondary Treatment ................................................................................................. 11
4.2.1 Site-Specific Suitability .................................................................................... 12
4.2.2 Description of Candidate Processes for Secondary Treatment ...................... 13
4.3 Disinfection ................................................................................................................. 16
4.4 Sludge Management ................................................................................................... 18
4.5 Secondary Treatment Option Evaluation ................................................................... 18
4.5.1 Qualitative Evaluation Factors ........................................................................ 18
4.5.2 Recommended Secondary Treatment Process ............................................... 19
CHAPTER 5 Preliminary Design .............................................................................................. 20
5.1 Preliminary Design Drawings ...................................................................................... 20
5.2 Unit Process Descriptions ........................................................................................... 20
5.2.1 Preliminary Treatment .................................................................................... 20
5.2.2 Secondary Treatment ..................................................................................... 20
5.2.3 Disinfection ..................................................................................................... 22
5.2.4 Sludge Management ....................................................................................... 23
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design ii
5.3 Facilities Description .................................................................................................. 23
5.3.1 Civil and Site Work .......................................................................................... 23
5.3.2 Architectural ................................................................................................... 24
5.3.3 Mechanical ...................................................................................................... 25
5.3.4 Electrical Service and Emergency Power ........................................................ 25
5.3.5 Lighting ........................................................................................................... 25
5.3.6 Instrumentation .............................................................................................. 26
5.4 Staffing Requirements ................................................................................................ 26
CHAPTER 6 Project Costs ....................................................................................................... 27
6.1 Opinion of Probable Capital Cost ................................................................................ 27
6.2 Opinion of Probable Operating and Life Cycle Cost .................................................... 27
6.3 Opinion of Annual Capital Replacement Fund Contributions ..................................... 29
CHAPTER 7 References .......................................................................................................... 30
Appendices
A Flow Data
B Environmental Risk Assessment
C Conceptual Plant Layout
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 3
CHAPTER 1 INTRODUCTION
1.1 Introduction
Harbour Engineering Joint Venture (HEJV) was retained by the Cape Breton Regional Municipality
(CBRM) to provide engineering services associated with the preliminary design of a wastewater
treatment plant (WWTP) for the community of Donkin, Nova Scotia as part of the greater
Environmental Risk Assessment and Preliminary Design of 7 Future Wastewater Treatment Systems
in CBRM project. This report will present preliminary design options for the new WWTP, as well as a
detailed discussion of the processes involved and their associated costs.
1.2 Background
The wastewater collection system in the community of Donkin, as in many communities throughout
CBRM, currently discharges untreated wastewater to the Atlantic Ocean. The evolution of the
existing wastewater collection and disposal systems in CBRM included the creation of regions of a
community which were serviced by a common wastewater collection system, tied to a local marine
outfall. Traditionally, such design approaches have been the most cost-effective manner of
providing centralized wastewater collection, and the marine environment has long been the
preferred receiving water given the available dilution. Due to a changing regulatory environment,
CBRM is working toward intercepting and treating the wastewater in these communities prior to
discharge.
1.3 Objectives
The objectives of this report will be to:
• Establish design parameters for a new WWTP;
• Evaluate treatment process alternatives; and
• Present a preliminary engineering design with capital and operating cost estimates, for a new
WWTP to meet the design requirements.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 4
CHAPTER 2 EXISTING CONDITIONS
2.1 Description of Existing Infrastructure
The Donkin wastewater collection system consists of approximately 7.3 km of gravity sewer, one lift
station, and 0.5 km of force main. All wastewater is directed to a 375 mm sewer that collects
wastewater from the end of Bastable and North Streets and conveys it to the discharge point. The
single lift station is located on the Donkin Highway across the street from Civic #383, and was
upgraded in 2010.
All wastewater is ultimately discharged untreated into the Atlantic Ocean at Borden’s Cove via a
concrete-encased outfall. The outfall is extended to a point where the obvert of the pipe is set at a
low water level, approximately 31 m off shore, according to the Donkin Sewage Disposal System As-
Constructed Drawings completed by C.A. Campbell Consultants Limited in 1976.
2.2 Flow Characterization
A flow meter was installed in the sewer system from March 13 through to May 1, 2018. The meter
location was just upstream of the discharge and encompasses the entire wastewater system. Flow
meter data is plotted in Appendix A.
The data was analyzed and the results are provided in Table 2.1. Per capita flows are calculated
assuming a current population of 471 people, and area-based flows are calculated using a total area
of 56.7 ha.
Table 2.1: Metered ADWF
Flow Category Metered Flow
(m³/day)
Per Capita Flow
(L/cap/day)
Areal Flow
(m³/ha/d)
Average Dry Weather Flow 199 422 3.5
Average Day Flow 466 989 8.2
Maximum Month Flow 628 1333 11.1
The Average Dry Weather Flow (ADWF) was defined as the average flow for the days that met the
following criteria:
• No rain recorded in the previous 24 hours;
• No more than 5 mm in the previous 48 hrs; and
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 5
• No more than 5 mm per day, additional, in all previous days (e.g., no more than 10 mm
altogether in the last 3 days).
The per capita measured ADWF is of 422 L/person/day. This is reasonable for dry weather flow
(compared to a reference value of 340 L/person/day), and indicates relatively low influence of
extraneous flows from inflow and infiltration (I&I) during dry weather.
The Average Day Flow (ADF) was calculated using all available metered flow data, including rain
events. The Maximum Month Flow (MMF) was calculated as the maximum flow measured during 30
consecutive days (April 1 – 30, 2018, which happened to coincide with a calendar month).
The peak day flow (PDF) for the metering period is provided in Table 2.2, measured as the maximum
flow in a 24-hour period. The PDF of 5,875 m3/d occurred during a large rain event (50.8 mm
according to Sydney A rain gauge, or 79.1 mm according to Sydney CS rain gauge); however, it was
less than a 1 in 2-year rain event.
Table 2.2: Metered PDF
48hr Rainfall (mm) PDF (m3/d) PDF (L/p/d) PDF (m3/ha/d)
51 5,875 12,473 103.6
The peak day flow is significant both in terms of a multiple of ADWF and per unit ha. The peak hour
flow was 473 m3/hr (131.5 L/s), as compared to an ADF of 466 m³/d (19.4 m³/hr). These flows were
metered after a 48-hour rainfall of 51 mm, strongly indicating that there is likely one or more
significant sources of inflow to the collection system. Efforts should be made to locate and minimize
the source(s) of inflow prior to detailed design, in order to reduce the capital cost and size of the
treatment plant. Roof leaders or sump pumps draining to the sewer may be contributing to this
peak flow.
2.3 Wastewater Quality Characteristics
HEJV collected one untreated wastewater sample upstream of the outfall in 2018, and the results
are summarized in Table 2.3. For simplicity, only the parameters of relevance to the preliminary
design are included. Refer to the Environmental Risk Assessment (ERA) report located in Appendix B
for the complete analytical results.
Table 2.3: 2018 Wastewater Characterization Results
Parameter Units April 2018
Carbonaceous Biochemical Oxygen Demand (CBOD5) mg/L 90
Total Kjeldahl Nitrogen (TKN) mg/L 9.7
Nitrogen (Ammonia Nitrogen) as N mg/L 2.9
Unionized Ammonia mg/L 0.0096
pH – 7.08
Total Phosphorus mg/L 1.5
Total Suspended Solids mg/L 50
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 6
Parameter Units April 2018
E. coli MPN/ 100mL >240,000
Total Coliforms MPN/ 100mL >240,000
CBRM collected a number of untreated wastewater samples from 2015 through 2018 and the
results are summarized in Table 2.4. Three samples from 2015 were removed from the data set
with high CBOD and TSS concentrations that were not considered to be representative of domestic
wastewater. None of the more recent samples displayed these characteristics.
Table 2.4: CBRM Wastewater Characterization Samples
Parameter Average Maximum Number of Samples
CBOD5 (mg/L) 81 370 60
TSS (mg/L) 79 890 60
Total Ammonia (mg/L) 5.1 7.9 9
Unionized Ammonia (mg/L) 0.008 0.014 11
pH (unitless) 6.8 7.0 9
2.4 Wastewater Loading Analysis
The theoretical per person loading rates listed in Atlantic Canada Wastewater Guidelines Manual
(ACWGM) (ABL Environmental Consultants Limited, 2006) are 0.08 kg CBOD/person/day and 0.09 kg
TSS/person/day. The reference theoretical TKN loading rate of 0.0133 kg TKN/person/day is stated
in Wastewater Engineering: Treatment and Reuse (Metcalf & Eddy, Inc, 2003)
Loads were calculated from three samples with concurrent flow data available. These samples were
collected in the D1 sewershed as identified in the Donkin Environmental Risk Assessment located in
Appendix B. The average value for 2018 was also calculated based on the calculated average flow
rate of the D1 sewershed (including all measured extraneous flows), and the average 2018 D1
concentration data. These values are shown in Table 2.5, below.
Table 2.5: Calculated and Theoretical Loading Rates
Calculated Load CBOD (kg/cap/d) TSS (kg/cap/d) TKN (kg/cap/d)
March 15, 2018 (D1) 0.04 0.03 –
March 29, 2018 (D1) 0.03 0.03 –
April 13, 2018 (D1) 0.03 0.03 –
April 24, 2018 (D1) 0.04 0.02 0.005
April 27, 2018 (D1) 0.01 0.01 –
Average 2018 (D1) 0.05 0.03 –
Average 2015-2018 (D1) 0.08 0.08 –
Theoretical Loading 0.08 0.09 0.013
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 7
For CBOD, TSS and TKN data from 2015, the theoretical loading rates appear to be higher than the
current data, however, concentrations in 2018 are lower than in previous years, and so may not be
representative. The reason for this is unknown, and the loading rates for previous years have
significant uncertainty because the flows were not measured; however, using the average
concentrations in combination with the metered ADF gives loading rates very similar to theoretical
rates. We recommend that additional sampling and concurrent flow monitoring is undertaken to
better establish the design loads prior to detailed design.
For design loading conditions, the theoretical values were used for CBOD, TSS, and TKN. The design
loading rates are shown in Table 2.6, below.
Table 2.6: Design Loading Rates
Parameter Value
Population 471
CBOD (kg/cap/d) 0.08
TSS (kg/cap/d) 0.09
TKN (kg/cap/d) 0.013
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 8
CHAPTER 3 BASIS OF DESIGN
3.1 Service Area Population
The primary method used to estimate future wastewater flows and loads is to project current per
capita flows and loads based on estimates of future population. The service area population for
Donkin was obtained based on the 2016 Census data from CBRM’s GIS database using the following
procedure: Each residential unit within the service area boundary from CBRM’s structure database
was multiplied by the average household size for the census dissemination area that it falls within.
For Donkin, the service area population was estimated to be 471 people in 256 residential units.
The population of the CBRM has been declining and this trend is expected to continue. The latest
population projection study, completed in 2018 by Turner Drake & Partners Ltd., predicted a 17.8%
decrease in population in Cape Breton County between 2016 and 2036. For this reason, no
allocation has been made for any future population growth. For the purpose of this pre-design
study, WWTP sizing will be based on the current population and measured flow data. While this
may seem overly conservative, due to significant amounts of inflow and infiltration (I&I) observed in
sewer systems in the CBRM, a given population decrease will not necessarily result in a proportional
decrease in wastewater flow. Therefore, basing the design on current conditions is considered the
most reasonable approach.
As the target date for this WWTP is 2040, consideration should be given to re-evaluating the
population and wastewater flows if a significant amount of time has passed between completion of
the pre-design study and the project moving to the detailed design stage.
3.2 Design Flows and Loads
As discussed in the Donkin Collection System Pre-Design Brief (Harbour Engineering Joint Venture,
2019), all flows will be conveyed to a central pump station that discharges to the proposed WWTP.
The Collection System Pre-Design Brief reported average wet weather flows of 8 – 20 L/s; therefore,
the pump station was sized for a maximum flow rate of 18 L/s. The pump station will provide some
storage to dampen effects of short term peak flows and is to be equipped with an overflow to by-
pass the WWTP during significant wet weather events or inflow. With a controlled pumped
discharge, the average daily flow rate and maximum monthly flow rate of the WWTP were
calculated without the effects of the significant weather events during the flow monitoring period.
The design average daily flow rate and maximum monthly flow rate of the WWTP are calculated to
be 360 and 400 m3/day, respectively, shown in Table 3.1, below. They are rounded for ease of use.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 9
Table 3.1: WWTP Design Flows
Parameter Value
Average Dry Weather Flow (m³/day) 200
Average Daily Flow (m³/day) 360
Maximum Monthly Flow (m³/day) 400
Peak Day Flow (m³/day) 1,550 (18 L/s)
Peak Hour Flow (m³/hr) 64.8
3.3 Effluent Requirements
The effluent requirements will include the federal Wastewater System Effluent Regulations (WSER)
limits, along with provincial effluent requirements determined by Nova Scotia Environment (NSE),
and presented in the future NSE Approval to Operate for the WWTP. An ERA which determined
effluent discharge objectives for parameters not included in the WSER is found in Appendix B.
The receiving water for the Donkin WWTP is Borden’s Cove in the Atlantic Ocean. The ERA generally
followed Technical Supplement 3 of the Canada-wide Strategy for the Management of Municipal
Wastewater Effluent – Standard Method and Contracting Provisions for the Environmental Risk
Assessment. Dilution modelling was conducted to determine the maximum 1 day average effluent
concentration, with a mixing zone boundary of 100 m for all parameters of concern with the
exception of E. coli for primary contact recreation. The E. coli concentration was analyzed at the
edge of the 100 m mixing zone for secondary contact recreation, and at Schooner Pond Beach for
primary contact recreation.
Refer to Table 5.1 in the ERA attached in Appendix B for Effluent Discharge Objectives (EDOs)
determined by the ERA, and for further information on the development of these values.
The effluent requirements are summarized in Table 3.2 along with the source of the criteria. As
EDOs are calculated values, they are not round whole numbers that are typical of effluent
requirements; therefore, we have included both the EDOs and values that are more suited as
effluent requirements in the table.
Table 3.2: Design Effluent Requirements
Parameter EDO Required By Effluent Limit
CBOD5 (mg/L) 25 WSER 25
TSS (mg/L) 25 WSER 25
Un-ionized Ammonia (as NH3-N, mg/L) 1.25 WSER 1.25
Total Residual Chlorine (TRC, mg/L) 0.02 WSER 0.02
E. coli (E. coli/ 100 mL) 262,069 NSE 200
3.4 Design Loads
The wastewater concentrations vary significantly as was shown in Sections 2.3 and 2.4. For design
purposes, we are going to use the calculated per person loads shown in Table 2.6. The maximum
month loads are assumed to be 1.2 times the average loads for all constituents. The resulting loads
are shown below in Table 3.3.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 10
Table 3.3: Design Loading Summary
Parameter Average Day Max. Month
Design Population 471
Flow (m3/day) 360 400
CBOD Load (kg/day) 38 46
TSS Load (kg/day) 42 50
TKN Load (kg/day) 6 8
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 11
CHAPTER 4 TREATMENT PROCESS ALTERNATIVES
Achieving the effluent criteria described in the preceding chapter requires the selection of an overall
wastewater treatment process that includes a secondary treatment process. Secondary treatment
processes are predominantly aerobic biological processes designed to convert the finely dispersed
and dissolved organic matter in wastewater into flocculent settleable biological cell tissue (biomass),
which can be removed by sedimentation. These biological processes are the most efficient in
removing organic substances that are either dissolved or in the colloidal size range (too small to
settle out), whereas primary treatment processes are the most efficient in removing larger particles
of suspended solids which can be removed by sedimentation, fine screening, or filtration.
4.1 Preliminary and Treatment
A variety of secondary treatment process options will be evaluated. Preliminary treatment
processes are typically used in advance of secondary treatment processes to remove objectionable
materials and inorganic particles from the wastewater prior to treatment. These processes may
include screening or coarse solids reduction, and grit removal.
Preliminary treatment requirements are dependent upon the secondary treatment technology that
is selected. For land-based treatment technologies, pre-treatment requirements can range from no
preliminary treatment, to a screen or grinder, to grit removal. The influent wastewater is conveyed
to the WWTP site via a centralized pump station as outlined in the Donkin Collection System Pre-
Design Brief (Harbour Engineering Joint Venture, 2019). Considerations for this site include that the
Donkin WWTP will be a CBRM satellite facility, so minimizing maintenance visits is desirable;
however, including a coarse bar screen would remove litter and other large, non-biodegradable
solids from the incoming flow. For this reason we have included a manually-raked coarse bar rack,
but it may be possible to operate without preliminary treatment, if preferred.
4.2 Secondary Treatment
There are many types of secondary treatment processes available, most of which can be classified as
either suspended growth or attached growth systems. Suspended growth systems use aeration and
mixing to keep microorganisms in suspension, and achieve a relatively high concentration of these
microorganisms (biomass) through the recycling process of biological solids. Attached growth
systems provide surfaces (media) on which the microbial layer can grow, and expose this surface to
wastewater for adsorption of organic material, and to the atmosphere and/or artificial aeration for
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 12
oxygen. A listing of specific secondary treatment processes and the category to which they belong is
presented in Table 4.1.
Table 4.1: Secondary Treatment Processes
Process Category Specific Process
Suspended Growth Activated Sludge
Extended Aeration
Pure Oxygen Activated Sludge
Sequencing Batch Reactor (SBR)
Oxidation Ditch
Membrane Bioreactor (MBR)
Attached Growth Rotating Biological Contactor (RBC)
Trickling Filter
Biological Activated Filter (BAF)
Moving Bed Bio-Reactor (MBBR)
Land-Based Stabilization Basin
Aerated Lagoon
Constructed Wetlands
HEJV has worked on projects using the majority of the technologies in Table 4.1 so we are able to
use our considerable practical experience to narrow down the list of available technologies to those
best satisfying the project constraints.
4.2.1 Site-Specific Suitability
The main constraints at this site will influence which of the available options are best suited for the
Donkin WWTP: effluent requirements, site conditions, cost effectiveness, and ease of operation.
Each of these items are discussed below.
4.2.1.1 EFFLUENT REQUIREMENTS
The effluent requirements summarized in Section 3.3 can be met by all of the listed technologies in
Table 4.1, with the exception of the land-based processes which may require a settling pond or
constructed wetland for additional polishing of the effluent.
4.2.1.2 SITE CONDITIONS
All of the land-based options require a significant amount of available land, with the stabilization
basin requiring a large amount of land, and the aerated lagoon requiring a moderate amount of
land. Constructed wetlands usually require even more land than stabilization basins, and work best
as a polishing process. Based on a preliminary review, a stabilization basin may be restricted by the
presence of wetlands, identified by provincial mapping, and setbacks and separation distances from
neighbouring residents.
A location to the northeast of Bastable Street has been identified as the preferred location of the
Donkin WWTP, since the existing outfall currently discharges in this area. The site selection is
described in the Donkin Collection System Pre-Design Report (Harbour Engineering Joint Venture,
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 13
2019). HEJV recommends CBRM purchase the privately owned PID 15494248, and CBRM owned PID
15277353. This location is remote from residential development, as defined as being at least 150 m
from isolated human habitation as required by the ACWGM (ABL Environmental Consultants
Limited, 2006). The location also provides adequate distance from neighboring property boundaries
as defined by ACWGM. The existing Donkin Sewer System and Donkin Interceptor Plan/Profile
Drawings in the Donkin Collection System Pre-Design Brief (Harbour Engineering Joint Venture,
2019) detail the proposed location of the new Donkin WWTP.
In the preferred location there are two identified coal seams; the Bouthillier and Back Pit seams.
Both of these seams have not officially been mined as the seams are quite thin; for this reason it is
unlikely any bootleg mining operations would have taken place.
4.2.1.3 COST EFFECTIVENESS
Of the processes listed in Table 4.1, many can be eliminated based on their cost effectiveness
compared to the other processes. The land-based treatment process options are generally the most
cost-effective to construct and operate, provided the technology is appropriate for the size of the
plant and there is sufficient available land suitable for construction.
4.2.1.4 EASE OF OPERATION
The operational requirements of both aerated lagoons and stabilization basins are much less
involved than a mechanical treatment plant. Of the two land based processes, stabilization basins
require less maintenance and operations due to the absence of an aeration system and blowers.
4.2.2 Description of Candidate Processes for Secondary Treatment
Based on the preceding analysis, the following processes should be given further consideration:
• Stabilization Basin; and
• Aerated Lagoon.
Each of these processes are described below.
As the treatment system will be a land-based system (lagoon), the hydraulic retention time will be
sized for the maximum monthly flow and average loads at winter temperatures. The aeration
component (if applicable), will be sized for summer temperatures. Individual facility components
such as piping and the UV disinfection system may be sized for different peak flows as appropriate.
Design temperatures for winter and summer are assumed to be 0.5°C and 20°C, respectively.
Winter conditions will govern the process requirements for lagoon size owing to the observed high
flows and loads in combination with the coldest temperatures. Warm water temperatures during
summer will determine aeration system requirements such as blower size, headers, number of grids,
and diffusers for the lagoons.
4.2.2.1 STABILIZATION BASIN
In stabilization basins, oxygen is supplied to the wastewater by algal respiration and directly from
the atmosphere, without mechanical aerators. Most of the oxygen from algal respiration is
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 14
produced near the surface, because the algae require sunlight. Diffusion of oxygen and mixing from
the wind are also highest near the surface. If a stabilization basin is shallow enough, it can be
aerobic throughout, but the most common type in this region is facultative. In a facultative
stabilization basin, the surface is aerobic, the middle has declining oxygen levels, and the bottom
layer is anaerobic, allowing for sludge digestion. Facultative stabilization basins are typically 1.5–
1.8 m deep, and have retention times in the range of 25 to 180 days, with 180 days being common
in Atlantic Canada. Only the facultative stabilization basin will be assessed (subsequently referred to
in this report as “Stabilization Basin”). Organic loading rates for areas with an average winter air
temperature of less than 0°C are typically in the range of 11–22 kg BOD5/ha/d. They have at least
two cells, while larger lagoons may have more cells to minimize short circuiting. Effluent suspended
solids can be seasonally high due to algae, but stabilization basins may be followed by a constructed
wetland for effluent polishing.
The stabilization basin is sized using the formula from ACWGM shown below in Equation 4.1 and
Equation 4.2, where Le is the effluent CBOD concentration (mg/L), Li is the influent CBOD
concentration (mg/L), KT is the reaction rate constant at temperature T (°C), T is the reaction
temperature (°C), t is the total retention time (days), n is the number of cells in series, and θ is a
temperature activity coefficient assumed to be 1.036. The resulting volume is targeting an effluent
concentration around 20 mg/L in winter, and includes allowances for sludge storage and ice
formation.
Equation 4.1
𝐿 =𝐿
ቀ1+𝐾்𝑡𝑛ቁ
Equation 4.2
𝐾் =𝐾ଶ𝜃ሺ்ିଶ ሻ
A stabilization basin conceptual option has been developed based on the projected design flow and
loads, as well as on the design parameters listed in Table 4.2.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 15
Table 4.2: Stabilization Basin Design Parameters
Parameter Value
Average Day Flow (m3/d) 360
Number of Cells 2
Reaction Rate Constant K₂₀ (/d) 0.055
Temperature – Winter/Summer (°C) 0.5 / 20
Total Volume (m³) 26,000
Retention Time at Average Flow (days) 72
Water Depth + Freeboard (m) 1.5 + 1
Side Slope 3:1
Area (at waterline, m²) 23,000 (2.3 ha)
Cell dimensions, per cell (at waterline, L x W, m) 65 x 177
Organic Loading Rate 16.6 kg/ha/d
Sludge allowance (m) 0.15
Ice allowance (m) 0.15
Wetlands can be used to provide additional removal of TSS. Constructed wetlands are inundated
land areas with water depths typically less than 0.6 m that support the growth of emergent plants
such as cattail, bulrush, reeds, and sedges. The wastewater flows gradually through the vegetation
and solids settle out in the wetland. In cold climates, the operating depth is normally increased in
the winter to allow for ice formation on the surface, and to provide the increased detention time
required at colder temperatures.
A conceptual wetland option has been developed based on the projected design flow and loads, as
well as on the design parameters listed in Table 4.3.
Table 4.3: Polishing Wetland Design Parameters
Parameter Value
Average flow (m3/day) 360
Retention Time (days) 1
Wetland Type Free Water Surface
Water Depth (m) 0.6
Total Area of Wetland Cells (m2) 600
4.2.2.2 AERATED LAGOON
In aerated lagoons, oxygen is supplied by mechanical aeration, which in newer systems is typically
subsurface diffused aeration. They have average retention times ranging from 5 to 30 days, with 30
days being common in Atlantic Canada. They accept higher loading rates than stabilization basins,
are typically at least 3 m deep, require less land, and are typically less susceptible to odours. They
also have higher operational costs. They can be either completely or partially mixed. Completely-
mixed aerated lagoons are rarely cost effective because they use significantly more energy than
partially-mixed aerated lagoons and require additional solids separation infrastructure; therefore,
only the partially-mixed aerated lagoon will be assessed (subsequently referred to in this report as
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 16
“Aerated Lagoon”). These aerated lagoons can include a quiescent zone as part of the main
treatment cells, or may be followed by a polishing pond or wetland to reduce suspended solids prior
to discharge.
The required retention times are calculated using Equations 4.1 and 4.2, above. The resulting
volume is targeting an effluent concentration around 20 mg/L in winter, and includes an allowance
for sludge storage.
A conceptual level cost estimate has been developed for this option based on the projected design
flow and loads, as well as on the design parameters listed in Table 4.4.
Table 4.4: Aerated Lagoon Design Parameters
Parameter Value
Maximum monthly flow (m3/d) 400
Number of Cells 4 aerated cells, 1 settling zone
Reaction Rate Constant K₂₀ (/d) 0.276
Temperature – Winter/Summer (°C) 0.5 / 20
Retention Time in Treatment Volume at Average
Flow/Max Month (days) 22 / 20
Treatment Volume (m³) 8,000
Total Volume including settling and sludge allowance (m³) 10,000
Water Depth + Freeboard (m) 3 + 1
Side Slope 3:1
Area (at top of berm, m²) 7,600
4.3 Disinfection
Disinfection at WWTPs is typically provided using either chlorination or ultraviolet (UV) disinfection.
Due to the total reduced chlorine (TRC) limit in the WSER, use of chlorine disinfection requires a
dechlorination system. In addition, a UV disinfection system is preferable from a safety perspective,
and minimizes chemical handling.
The UV system has been sized to achieve effluent limits of 200 E. coli/100mL. UV disinfection is a
physical disinfection process that targets microorganisms such as viruses, bacteria, and protozoa by
destroying their ability to reproduce. Pathogen inactivation is directly linked to UV dose, which is
the product of the average UV intensity, and the duration of exposure, or retention time. Any factor
affecting light intensity or retention time will also affect disinfection effectiveness. Some of the key
parameters that affect UV intensity include water quality issues such as:
• UV transmission;
• Suspended solids;
• Presence of dissolved organics, dyes, etc.;
• Hardness; and
• Particle size distribution.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 17
Other factors affecting UV performance include sleeve cleanliness, age of lamps, upstream
treatment processes, flow rate, and reactor design.
Flows from either the aerated lagoon or stabilization basin system will flow continuously by gravity
to the UV disinfection unit. Disinfection will take place in a single channel located in a building and
due to the low design UV transmission (%UVT) from these options, two banks of lamps are required.
The lamps are oriented horizontally and parallel to the direction of flow. The disinfected effluent
would flow by gravity to the outfall. The design parameters for the UV disinfection system are
summarized in the Table 4.5 below.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 18
Table 4.5: UV Disinfection Design Parameters
Parameter Design Value
Number of Design Channels 1
Number of Banks 2
Number of Lamps per Bank 24
Total Number of Lamps 48
Peak Flow Capacity (m3/d) 1,555
Effluent TSS (mg/L) <25
Minimum Transmission (%UVT) 40
Effluent E. coli (MPN/100 mL) 200
4.4 Sludge Management
Sludge Management is an important variable to consider when investigating treatment options, as
sludge handling and disposal costs can constitute a large portion of a WWTP’s annual operating
budget. With either an aerated lagoon or stabilization basin, sludge is removed from the treatment
process on an infrequent basis compared to mechanical treatment plants.
Sludge must be removed periodically from the treatment system and disposed of at an approved
facility. Sludge management costs are greatly dependent on the quantity and quality of sludge
produced. Due to their long retention times and in-situ digestion, the two land-based technologies
under consideration are expected to produce less sludge than a mechanical treatment system.
Waste sludge volume from an aerated lagoon or stabilization basin in this sewershed is expected to
be approximately 800 m3 sludge in 10 years.
Sludge management options include composting, geotextile bag stabilization, and digestion, at
either local or regional facilities. The recommended sludge management approach for all of CBRM’s
facilities is being evaluated as a separate component of this project. Due to the relative size of the
Donkin WWTP and the infrequent requirement for sludge removal, no sludge thickening, or solids
handling has been included for this plant.
4.5 Secondary Treatment Option Evaluation
Both options were laid out on the site. The overall footprint of the stabilization basin is much larger
than that of the aerated lagoon, affecting the volume of borrow required on site as well as the
footprint encroaching on existing wetlands. Due to the following site constraints, including
regulatory setbacks from residential areas, eroding coastline, and nearby wetlands, a stabilization
basin could not reasonably fit on the site and would not make it an economically feasible option.
Therefore, only the aerated lagoon option was carried out for capital and operating cost estimates.
In the event that existing wetland area is affected, compensation wetlands are required to be
constructed with the approval of Nova Scotia Environment.
4.5.1 Qualitative Evaluation Factors
In addition to cost, there are a number of other factors to consider when evaluating the technology
options that are less easily quantified. These factors are summarized in Table 4.6, and additional
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 19
discussion is provided below. Qualitative factors have been rated 1 or 2 for each technology with 1
being the best and 2 being the worst.
Table 4.6: Secondary Process Qualitative Evaluation Factors
Factor Aerated Lagoon Stabilization Basin
Local Experience with Process 2 1
Operational Simplicity 2 1
Sludge Production 2 1
Site Aesthetics 1 2
In terms of local experience with the treatment process, CBRM have experience with stabilization
basins at Meadowbrook, Tower Road, Reserve Mines (Centreville), Birch Grove, and also with an
aerated lagoon at Southwest Brook.
When considering operational simplicity, although both processes are fairly straightforward, the
stabilization basin option has the benefit of not having an aeration component.
Each of the secondary treatment processes evaluated will produce sludge that will have to be
removed from the process. The longer HRT provided in the stabilization basin will result in a slightly
lower sludge production than the aerated lagoon.
When considering site aesthetics, the aerated lagoon is more compact than the stabilization basin
and is less susceptible to odours. The preferred site has wetlands identified on provincial mapping
that limit the available footprint to accommodate a stabilization basin. The separation distance
required for a stabilization basin in the ACWGM is 150 m from isolated residences, and 300 m from
built-up areas. Stabilization basins are also susceptible to odour problems.
Land procurement would be somewhat simpler with the aerated lagoon because it can be built on
fewer properties, without having to buy land from so many owners to put together a parcel large
enough to accommodate the larger footprint of the stabilization basin.
As previously discussed, the site topography, regulatory setbacks from residential areas, eroding
coastline, and nearby wetlands limit the feasibility of a stabilization basin fitting on the site and
make it not an economically feasible option. Stabilization basins do have a number of advantages,
including extensive CBRM experience, lower sludge production, and operational simplicity, but these
would not offset the significant aesthetic, regulatory disadvantages, and cost implications in this
case. Therefore, the aerated lagoon option will be carried forward for pre-design.
4.5.2 Recommended Secondary Treatment Process
HEJV recommends an aerated lagoon for the Donkin WWTP. The selection of this process was
ultimately determined by costs, site topography, land procurement considerations, and aesthetics,
including ACWGM separation distances, odour risks, and proximity to neighbouring properties.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 20
CHAPTER 5 PRELIMINARY DESIGN
5.1 Preliminary Design Drawings
Preliminary layouts for the proposed treatment system and locations of individual unit processes are
shown in the “Preliminary Design” drawings, found in Appendix C. The processes depicted in these
drawings are consistent with those recommended in the previous chapter of this report. The
drawings contained in the appendix are presented in Table 5.1, below.
Table 5.1: Preliminary Design Drawings
Drawing Number Description
C01 General Arrangement
C02 Proposed WWTP
C03 Sewer Profiles and Lagoon Sections
5.2 Unit Process Descriptions
Drawing C01 and C02 in Appendix C include a site plan showing the location of the proposed new
WWTP. Further description of the proposed treatment units follows.
5.2.1 Preliminary Treatment
All wastewater will be conveyed to a central pump station that will discharge to the WWTP site. The
pump station will discharge into an influent chamber positioned at the inlet of the plant. The
influent chamber will be concrete and drop the flow to the elevation to be gravity fed to the lagoon
under the lagoon’s surface. As the Donkin WWTP site is a satellite plant, CBRM has requested that
the level of maintenance and operations be reduced as much as reasonably and practically possible.
Including a coarse bar screen in the influent chamber would remove litter and other large solids
from the incoming flow, and prevent them from having to be removed from the surface of the
lagoon later on. For this reason, we have included a manually-raked coarse bar rack, but it may be
possible to operate without preliminary treatment, if preferred.
5.2.2 Secondary Treatment
The secondary treatment process will consist of three aerated lagoon basins divided into four
aerated cells and one quiescent settling cell by means of berms or floating baffles. All cells will be
partially mixed, with the exception of the settling zone. The first two cells will operate in parallel,
followed by the last two cells in series. This will allow any of the basins to be independently isolated
for sludge removal or for maintenance. Enough air will be provided to the aerated cells to meet
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 21
CBOD removal requirements and opportunistic nitrogen removal during the summertime. Control
over process flows within the treatment plant will be provided through effluent weirs in the control
manholes and the effluent chamber that will control the discharge flow and the water levels in the
aerated lagoon basins.
Each aerated cell will provide an average of 5 days of retention time at the maximum monthly
design flows. All of the readily biodegradable CBOD and most of the slowly biodegradable CBOD will
be consumed in the first four cells, and a significant portion of solids will become solubilized and
treated in the first four cells.
The fourth cell will also contain an effluent polishing zone and will be separated from the third cell
by means of a floating curtain or baffle, anchored at the top and weighted at the bottom. The
floating baffles serve to minimize hydraulic short circuiting. The settling zone is a non-aerated cell,
sized for one day of retention, which is suitable for further settling of TSS and some further
degradation of pollutants. The settling zone hydraulic retention time is approximately one day of
storage at maximum monthly design flows, and is short enough to minimize algae growth during the
warmest months.
The aerated lagoon will be configured to allow bypassing for emergency maintenance. Table 5.2
outlines the aerated lagoon design parameters.
Table 5.2: Secondary Treatment – Aerated Lagoon Design Summary
Parameter Design Value
Maximum Monthly Flow (m3/d) 400
No. of Cells 4 aerated cells, 1 settling zone
Total Volume (m3) 10,000
Volume (m3, per aerated cell) 2,000
Retention Time at Average Flow/Max Month (days) 22 / 20
Depth (m) 3.00
Freeboard (m) 1.00
Side Slope 3:1
Total Area (at top of berm, m²) 7,600
Peak Oxygen Required (kg O2/day) 150
Peak Air Required (SCFM) 250
A subsurface investigation is required to investigate soil conditions, assess bearing capacity, and
determine the depth to groundwater and bedrock. For the purposes of this report and due to the
evidence of nearby wetlands, we have assumed that the water table is at the elevation of grade. If
bedrock or groundwater elevations are found to vary from the surface, then the aerated lagoon
grade line and collection system layout may need to be adjusted to accommodate the site
conditions; this may reduce quantity of fill requirements. For the purpose of this pre-design it is
assumed a 60 mil HDPE membrane liner is required, and that some localized drainage may be
required to lower the groundwater level underneath the lagoon.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 22
5.2.2.1 AERATION SYSTEM
The aeration system will include fine bubble diffusers suspended from floating laterals. Fine bubble
aeration is more efficient compared to coarse bubble aeration due to the increased surface area of
the bubbles, the longer time it takes for the bubbles to rise to the surface, and coarse bubble
aeration is more efficient than surface aeration. There are a number of advantages with this type of
system including:
• Improved performance and energy efficiency over coarse bubble or mechanical aeration
systems;
• Resistance to fouling;
• System is retrievable;
• Equipment can be installed or diffusers replaced while the lagoons are in operation;
• System is less sensitive to undulations in the lagoon bottom;
• Improved air distribution, mixing and control capability; and
• Individual diffuser chains can be isolated for greater operational flexibility.
Low pressure air will be delivered by blowers through a system of headers, manifolds, distribution
pipe, and floating laterals. The floating laterals will extend across the lagoon cells and deliver
process air to membrane diffusers that are suspended from the laterals. Diffuser location and
distribution of air will be tapered to provide increased aeration at the beginning of the process and
less air farther into the treatment process. Cell #1 and Cell #2 (parallel) will contain the highest
density of diffusers and will be governed by process air requirements. Cell #3 and Cell #4 will have
significantly lower diffuser density (number of diffusers per square meter) that will be gradually
tapered as governed by process air requirements.
The plant has been designed to operate with one duty blower, and a second standby blower in the
event of failure of the duty blower. It is recommended that the blowers operate with variable
frequency drives (VFDs). VFDs improve process control by controlling the speed of the blower, and
can thereby provide energy savings, and reduce wear and tear on motors. Space will be allowed for
a third blower in the event of future demand.
5.2.3 Disinfection
Effluent leaving the settling cell will flow continuously by gravity to the ultraviolet (UV) disinfection
unit. The UV disinfection unit will be installed in a single stainless steel channel located in the
proposed process building. The UV system will consist of two banks of UV lamps. The lamps are
oriented horizontally and parallel to the direction of flow and contain 24 lamps per bank for a total
of 48 lamps. The UV weir height is a factor in setting the hydraulic grade line for the rest of the
treatment process. The design parameters for the UV disinfection system are summarized in Table
5.3.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 23
Table 5.3: UV Disinfection Design Summary
Parameter Design Value
Average Flow (m3/d) 360
Peak Flow Capacity (m3/d) 1550
Number of Channels 1
Number of Banks 2
Number of Lamp per Bank 24
Total Number of Lamps 48
Effluent TSS (mg/L) <25
Minimum UV Transmission (%UVT) 40
Effluent Fecal Coliforms (MPN / 100 mL) 200
5.2.4 Sludge Management
Sludge must be removed periodically from the treatment system and disposed of at an approved
facility. Sludge management costs are greatly dependent on the quantity and quality of sludge
produced. Approximately 1,600 kg of solids are expected to accumulate in 15 – 20 years of
operation. It is assumed that the solids will be dredged approximately every 15 years.
Sludge management options include composting, geotextile bag stabilization, and digestion, at
either local or regional facilities. The recommended sludge management approach for all of CBRM’s
facilities is being evaluated as a separate component of this project. Due to the relative size of the
Donkin WWTP and the infrequent requirement for sludge removal, it is expected that no local
sludge management facility will be located at this plant.
5.3 Facilities Description
The WWTP project will include the following facilities, which are further described below:
• Site access and parking;
• Site fencing;
• Aerated lagoon cells and a settling cell;
• Yard piping; and
• Process building, containing the following items:
o Blowers;
o UV disinfection area;
o Instrumentation and Controls;
o Sample location;
o Administration and storage area; and
o Washroom and sump with submersible pump.
5.3.1 Civil and Site Work
Civil and site work will include grading, drainage and site improvements. An access road will be
constructed around the perimeter of the WWTP to provide vehicle access. A laydown area for
desludging equipment will be included.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 24
A significant amount of imported fill will likely be required to give the required vertical separation to
assumed bedrock and groundwater at this site. The top of berm will be at an elevation of 16.7 m,
and the bottom of the aerated lagoon will be at 12.7 m. It should be noted that the existing Atlantic
Canada Wastewater Guidelines Manual is currently under review, and it is possible that this review
may change the requirement of a one meter buffer clearance from the bottom elevation of the
lagoon to the water table with the installation of a liner. If the Guidelines are revised, the volumes
of imported fill would be reduced, subsequently providing significant cost savings. However, for the
purpose of this pre-design report the water table was assumed to be at grade level, due to the
presence of nearby provincially mapped wetlands.
Yard piping will be HDPE for the air piping, and 200 mm diameter SDR 28 PVC for buried influent and
effluent pipework. All valves will be accessible to the operator.
An impermeable 60 mil HDPE membrane liner has been carried in the cost estimate.
Security fencing will surround the lagoon cells and process building, installed at the top outside edge
of the berm.
The Environmental Risk Assessment that was carried out for this system was completed on the basis
of a discharge through an outfall into the receiving environment approximately 100 m from the
shore to achieve the recommended one metre depth above the pipe. The existing outfall only
extends approximately 32 m from the shore and the top of the pipe is at the low-water level;
therefore, we have included for outfall extension work. It is possible that the existing outfall is
considered to be acceptable by NSE and no further extension required, pending further assessment
of the environmental risk of this approach. However, for the purpose of this pre-design report an
extension of the existing outfall until the invert has a one metre depth clearance of the low water
level. The new outfall would likely include a new HDPE outfall pipe, stone mattress, concrete pipe
anchors, and armour stone protection. The approximate routing of the proposed treated
wastewater outfall is shown on Drawing C03 – Site Works Plan in Appendix C.
5.3.2 Architectural
The exterior wall system will be masonry block with polystyrene insulation to meet the
requirements of the current building code. The exterior face of the building envelope will be a brick
veneer similar to other WWTPs within CBRM. The roof will be a 5:12 pitched roof with pre-
engineered wooden trusses, complete with steel roofing. Interior doors and frames will be
galvanized steel with a factory applied paint finish. Windows and louvers will be anodized aluminum
to match existing features.
Interior walls will be concrete block with an industrial enamel finish. Interior metal surfaces will be
painted with epoxy paint and exterior metal will be finished with ultraviolet-resistant urethane
paint. Process Area ceilings will be finished with an industrial enamel paint. Process Area floors will
be concrete and will be finished with either a concrete floor hardener or an industrial high build
epoxy finish depending on requirements.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 25
5.3.3 Mechanical
Potable water will be required at the site, and will be provided from an approximately 250 m water
service connection to the distribution system on Bastable Street. Wastewater will be pumped from
a sump using a submersible pump to the influent chamber at the head of the plant.
Heating and ventilation will be provided by electric unit heaters and an exhaust fan.
Mechanical systems will be designed in accordance with NFPA 820, 2016 edition, which describes
the hazard classification of specific areas and processes, and prescribes ventilation criteria for those
areas. Table 5.4 summarizes the proposed classification for new facilities.
Table 5.4: Classification of Building Areas
Location Classification
UV Room Unclassified
Blower Room Unclassified
5.3.4 Electrical Service and Emergency Power
There is 3-phase electrical service available on the Donkin Highway at the end of Bastable Street and
it will need to be extended to the site.
The WWTP will be equipped with a backup generator to maintain functionality of critical process
equipment, including lift station, blowers, UV disinfection, and flow measurement instrumentation,
and building services including freeze-protection heating. An automatic power transfer switch will
transfer the process building’s power supply to the generator during a power disruption and will
return to normal operation when power has been restored. The emergency generator will be
located outside the Process Building in a weather proof enclosure and complete with noise
suppression.
5.3.5 Lighting
Exterior lighting will consist of building mounted luminaires illuminating areas immediately adjacent
the building, as well as pole mounted area lighting for access roadways and parking area. Exterior
lights will be LED where available or to suit application. Exterior lighting fixtures shall be vandal
resistant and outdoor rated.
The interior lighting system will be designed for lighting performance and illuminance levels in
accordance with the Illuminating Engineering Society (IESNA) Lighting Handbook, 10th Edition.
Interior lights will be fluorescent, LED or metal halide to suit the application.
Emergency and exit lights will be installed along egress routing and around exit doors to meet the
requirements of the National and Provincial Building Codes.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 26
5.3.6 Instrumentation
All equipment should be controlled via local control panels mounted inside the Process Building in
close proximity to the related equipment. The control panels for the UV Disinfection unit
equipment, flow meter, and blowers should be vendor supplied and designed to be integrated with
CBRM Electrical, Controls, and SCADA Standards.
The controls for the central pump station discharging to the WWTP, equipped with duplex pumping
system, will be located in the process building and will have a dedicated control panel equipped with
flow controls and level alarms.
5.4 Staffing Requirements
Staffing at wastewater treatment plants will vary depending on a number of factors including the
following:
• Plant classification (I, II, III or IV);
• Plant size and treatment capacity;
• Laboratory requirements;
• Complexity of the unit processes;
• Level of automation;
• Maintenance of peripheral facilities such pumping stations, collection systems, septage
receiving, etc.;
• Sensitivity of the receiving waters; and
• Variation in flows and loads to the plant i.e. Industrial, municipal, storm water component.
Based on the Points Classification System in the ACWGM (Appendix A), the proposed WWTP is likely
to be ranked as a Class I level treatment plant by the regulators, and require at least a Class I
operator to oversee the WWTP. Class I plants of this size typically require about 1200 hours of
maintenance per year, or approximately half of a full-time position.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 27
CHAPTER 6 PROJECT COSTS
6.1 Opinion of Probable Capital Cost
An opinion of probable capital cost for the recommended treatment process option is presented in
Table 6.1, detailed on the next page. Please note that the costs of interception and pumping are extra
and are detailed in Donkin Collection System Pre-Design Brief (Harbour Engineering Joint Venture,
2019). Please note that the capital costs given are in 2019 dollars, and would typically be inflated at a
rate of approximately 3% per year going forward to the intended construction year (or indexed using the
actual construction cost index ratio if calculating the probable construction cost at a specific point after
2019).
6.2 Opinion of Probable Operating and Life Cycle Cost
An annual operating cost estimate for the recommended treatment process option is presented in
Table 6.2.
Table 6.2: Operating Cost Estimate
Category Annual Operation Cost
Staffing $50,000
Power $13,400
Sludge Disposal $1,100
Maintenance Allowance $3,000
Total $67,500
Project Manager: D. McLean
Est. by: A. Thibault/L. Jenkins
PROJECT No.: 187116 (Dillon)
182402.00 (CBCL)
UPDATED: February 28, 2020
1.0 662,000$
allow 1 115,000$ 115,000$
allow 10% 546,800$
2.0 3,784,000$
m2 24,000 5$ 120,000$
m3 excavated 200 20$ 4,000$
Fill - Borrow m3 filled 200 10$ 2,000$
Fill - Imported m³ filled 76,000 30$ 2,280,000$
Liner and baffles m2 8,300 12$ 99,600$
m3 54 40$ 2,160$
m 200 400$ 80,000$
Inlet/Outlet Chamber allow 2 20,000$ 40,000$
m 350 340$ 119,158$
m 220 600$ 132,000$
m 80 100$ 8,000$
m 200 150$ 30,000$
m 200 60$ 12,000$
ea.7 6,000$ 42,000$
m 530 100$ 53,000$
allow 1 20,000$ 20,000$
allow 1 20,000$ 20,000$
allow 1 20,000$ 20,000$
Outfall Upgrade allow 1 700,000$ 700,000$
3.0 44,000$
m3 of baseslab 20 650$ 13,000$
m3 of concrete 30 900$ 27,000$
allow 10% 4,000$
4.0 70,000$
m2 wall area 151 170$ 25,704$
m2 wall area 138 323$ 44,514$
5.0 47,000$
m2 building area 90 409$ 36,799$
allow 10,000$
6.0 44,000$
m2 building area 90 40$ 3,600$
m2 building area 90 65$ 5,850$
m2 building area 90 43$ 3,874$
m2 building area 90 108$ 9,684$
m2 building area 90 15$ 1,350$
each 3 2,000$ 6,001$
each 2 1,100$ 2,200$
each 2 2,200$ 4,400$
m2 building area 90 75$ 6,750$
7.0 280,000$
each 1 195,750$ 195,750$
each 1 63,855$ 63,855$
each 1 20,000$ 20,000$
8.0 238,000$
m2 building area 90 470$ 42,300$
allow 30% of equipment 30% 84,000$
allow 40% of equipment 40% 112,000$
9.0 961,000$
allow 15% of project cost 15% 676,050$
allow 3% of project cost 3% 135,210$
allow 150,000$
6,130,000$
A 25% 1,533,000$
B 12% 736,000$
C 12,500$
8,411,500$
15%1,262,000$
9,673,500$
Note 1 A Design Development Contingency is to allow for necessary increases of qty's; construction costs; as the work is better defined
Note 2 A Construction Contingency is to allow for cost of additional work over and above the contract Awarded price.
Note 3 The Escalation/Inflation allowance is for increases in construction costs from time the budget to Tender Call
Note 4 The Location Factor is for variances between constr. costs at the location of the project & historical costs data
Form CBCL 034.Rev 0
Generator
UNIT UNIT COST
Reinstatement
Gravel (beneath slabs)
Ditching
Water Service
Gravel Road
Pressure sewer from sump in process building
Yard pipework (200 mm PVC)
Flow measurement
Table 6.1
PREPARED FOR:OPINION OF PROBABLE CONSTRUCTION COST
Class C Preliminary Budget
Cape Breton Regional MunicipalityDonkin, NS
Total
Site Works
EST. QUANTITY
Wastewater Treatment System Costs Only
ITEM / No.DESCRIPTION
Dewatering
Sediment Control
Mobilization, Bonds, Insurance, P.C. Mngmt
Contractor Overhead & Fees
Clear Grub; Site Preparation
Excavation
Chainlink Fence and Gates
Manholes
Aeration Header (200 mm HDPE)
Finishes/Doors/Windows
Miscellaneous Metals Items
Masonry
Carpentry, Assessories and Fixtures
Louvers
Painting
Epoxy Coating
Floor Finishes (Lab, Office, Admin Area)
Interior Masonry
Concrete
Roof (Pre-Eng Wood Trusses and steel roofing)
Foundation and Exterior Building Walls
Slab on Grade (building)
Miscellaneous Concrete Items
Exterior Masonry
Metals & Roofing
Electrical
Power Supply & Distribution
Process Mechanical
Windows (exterior - single)
Doors (single swing steel)
Construction Contingency
General Conditions
CONTINGENCIES and ALLOWANCES
Instrumentation & Control
Process Installation
UV Disinfection System
Door (double swing steel)
Other Interior Finishes, Misc
Process Equipment Supply
Aeration Equipment
Mechanical
HVAC and Plumbing
THIS OPINION OF PROBABLE COSTS IS PRESENTED ON THE BASIS OF EXPERIENCE, QUALIFICATIONS, AND BEST JUDGEMENT. IT HAS BEEN PREPARED IN ACCORDANCE WITH ACCEPTABLE
PRINCIPLES AND PRACTICES. MARKET TRENDS, NON-COMPETITIVE BIDDING SITUATIONS, UNFORSEEN LABOUR AND MATERIAL ADJUSTMENTS AND THE LIKE ARE BEYOND THE CONTROL
OF HEJV. AS SUCH WE CANNOT WARRANT OR GUARANTEE THAT ACTUAL COSTS WILL NOT VARY FROM THE OPINION PROVIDED.
Taxes (HST)
TOTAL DIRECT & INDIRECT CONSTRUCTION COST (Exluding Contingencies and Allowances)
TOTAL CONSTRUCTION & DESIGN COST without HST
TOTAL CONSTRUCTION & DESIGN COST with HST
Land Purchase
Engineering
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 29
6.3 Opinion of Annual Capital Replacement Fund Contributions
The CBRM wishes to create a Capital Replacement Fund to which annual contributions would be made
to prepare for replacement of the wastewater assets at the end of their useful life. The calculation of
annual contributions to this fund involves consideration of such factors as the type of asset, the asset
value, the expected useful life of the asset, and the corresponding annual depreciation rate for the
asset, as per the accounting practices for asset depreciation and Depreciation Funds recommended in
the Water Utility Accounting and Reporting Handbook (Nova Scotia Utility and Review Board, 2013). In
consideration of these factors, Table 6.3 provides an estimation of the annual contributions to a capital
replacement fund for the proposed new wastewater treatment system infrastructure. This calculation
also adds the same contingency factors used in the calculation of the Opinion of Probable Capital Cost,
to provide an allowance for changes during the design and construction period of the WWTP. The actual
Annual Capital Replacement Fund Contributions will be calculated based on the final constructed asset
value, the type of asset, the expected useful life of the asset, and the corresponding annual depreciation
rate for the asset type.
Table 6.3: Annual Capital Replacement Fund Contributions
Description of Asset Asset Value
Asset Useful
Life
Expectancy
(Years)
Annual
Depreciation
Rate (%)
Annual Capital
Replacement Fund
Contribution
Treatment Linear Assets
(Outfall and Yard Piping,
Manholes and Other)
$4,446,000 75 1.3% $58,000
Treatment Structures
(Concrete Chambers,
etc.)
$205,000 50 2.0% $5,000
Treatment Equipment
(Mechanical / Electrical,
etc.)
$1,479,000 20 5.0% $74,000
Subtotal $6,130,000 - - $137,000
Construction Contingency (Subtotal x 25%): $35,000
Engineering (Subtotal x 12%): $17,000
Opinion of Probable Annual Capital Replacement Fund Contribution: $189,000
Table Notes
1. Annual contributions do not account for annual inflation.
2. Costs do not include applicable taxes.
Harbour Engineering Joint Venture Donkin WWTP Preliminary Design 30
CHAPTER 7 REFERENCES
ACWGM. (2006). Atlantic Canada Wastewater Guidelines Manual for Collection, Treatment and
Disposal. Environment Canada.
CBCL Limited. (2018). Glace Bay Harbour Coastal Study – Final Report. Halifax: CBCL Limited.
Harbour Engineering Joint Venture. (2019). Donkin Collection System Pre-Design Brief.
Harbour Engineering Joint Venture. (2019). New Victoria Collection System Pre-Design Brief.
Metcalf & Eddy, Inc. (2003). Wastewater Engineering: Treatment and Reuse. New Delhi: Tata
McGraw-Hill.
Nova Scotia Utility and Review Board. (2013). Water Utility Accounting and Reporting Handbook.
UMA Engineering Limited. (1994). Industrial Cape Breton Wastewater Characterization Programme
– Phase II.
Harbour Engineering Joint Venture Appendices
APPENDIX A
Flow Data
0
10
20
30
40
50
60
70
800
1,000
2,000
3,000
4,000
5,000
Mar/13 Mar/20 Mar/27 Apr/03 Apr/10 Apr/17 Apr/24 May/01
Precipitation
Flow (m³/d)
Snow on Ground (cm)Rainfall (mm)Metered Flow
Harbour Engineering Joint Venture Appendices
APPENDIX B
Environmental Risk Assessment
182402.00 ● Report ● April 2020
Donkin Wastewater Treatment Plant
Environmental Risk Assessment
Final Report
Prepared by:
Prepared for:
March 2020
Final April 14, 2020 Darrin McLean Karen March Holly Sampson
Draft for Review June 27, 2018 Darrin McLean Karen March Holly Sampson
Issue or Revision Date Issued By: Reviewed By: Prepared By:
This document was prepared for the party indicated
herein. The material and information in the
document reflects HE’s opinion and best judgment
based on the information available at the time of
preparation. Any use of this document or reliance
on its content by third parties is the responsibility of
the third party. HE accepts no responsibility for
any damages suffered as a result of third party use
of this document.
182402.00
March 27, 2020
275 Charlotte Street
Sydney, Nova Scotia
Canada
B1P 1C6
Tel: 902-562-9880
Fax: 902-562-9890
_________________
182402 RE 001 FINAL WWTP ERA DONKINKM2.DOCX/mk
ED: 14/04/2020 15:01:00/PD: 14/04/2020 15:01:00
April 14, 2020
Matt Viva, P.Eng.
Manager Wastewater Operations
Cape Breton Regional Municipality (CBRM)
320 Esplanade,
Sydney, NS B1P 7B9
Dear Mr. Viva:
RE: Donkin Wastewater Treatment Plant ERA – Final Report
Enclosed, please find a copy of the Environmental Risk Assessment (ERA) Report
for the Donkin Wastewater Treatment Plant (WWTP).
The report outlines Environmental Quality Objectives (EQOs) for all parameters
of potential concern listed in the Standard Method for a “very small” facility.
Environmental Discharge Objectives (EDOs) were also calculated for all
parameters of potential concern.
If you have any questions or require clarification on the content presented in
the attached report, please do not hesitate to contact us.
Yours very truly,
Harbour Engineering
Prepared by: Reviewed by:
Holly Sampson, M.A.Sc., P.Eng. Karen March, M.Sc.
Intermediate Chemical Engineer Environmental Scientist
Direct: 902-539-1330 Phone: 902-450-4000
E-Mail: hsampson@cbcl.ca E-Mail: kmarch@dillon.ca
Project No: 182402.00
March 27, 2020
Harbour Engineering Joint Venture Donkin WWTP ERA i
Contents
CHAPTER 1 Background and Objectives ......................................................................................... 1
1.1 Introduction ........................................................................................................................ 1
1.2 Background ......................................................................................................................... 1
1.3 Facility Description .............................................................................................................. 2
CHAPTER 2 Initial Wastewater Characterization ............................................................................ 4
2.1 Substances of Potential Concern ........................................................................................ 4
2.1.1 Whole Effluent Toxicity ........................................................................................... 5
2.2 Wastewater Characterization Results ................................................................................ 5
CHAPTER 3 Environmental Quality Objectives ............................................................................... 7
3.1 Water Uses .......................................................................................................................... 7
3.2 Ambient Water Quality ....................................................................................................... 8
3.3 Physical/ Chemical/ Pathogenic Approach ....................................................................... 10
3.3.1 General Chemistry/ Nutrients .............................................................................. 10
3.3.2 E. coli ..................................................................................................................... 14
3.3.3 Summary ............................................................................................................... 14
CHAPTER 4 Mixing Zone Analysis ................................................................................................. 16
4.1 Methodology ..................................................................................................................... 16
4.1.1 Definition of Mixing Zone ..................................................................................... 16
4.1.2 Site Summary ........................................................................................................ 18
4.1.3 Far-Field Modeling Approach and Inputs ............................................................. 18
4.2 Modeled Effluent Dilution ................................................................................................ 21
CHAPTER 5 Effluent Discharge Objectives .................................................................................... 24
5.1 The Need for EDOs ............................................................................................................ 24
5.2 Physical/ Chemical/ Pathogenic EDOs .............................................................................. 24
5.3 Effluent Discharge Objectives ........................................................................................... 25
CHAPTER 6 Compliance Monitoring ............................................................................................. 26
CHAPTER 7 References ................................................................................................................ 27
Appendices
A Laboratory Certificates
Harbour Engineering Joint Venture Donkin WWTP ERA 1
CHAPTER 1 BACKGROUND AND OBJECTIVES
1.1 Introduction
Harbour Engineering (HE) was engaged by the Cape Breton Regional Municipality (CBRM) to complete
an Environmental Risk Assessment (ERA) for the proposed Donkin Wastewater Treatment Plant
(WWTP). As this is a proposed WWTP that has not yet been designed, this ERA was completed with the
objective that it serve as a tool to establish effluent criteria for the design of a new WWTP. For this
reason, the ERA was completed without the frequency of testing required by the Standard Method
outlined in Technical Supplement 3 of the Canada-wide Strategy for the Management of Municipal
Wastewater Effluent (Standard Method) for initial wastewater characterization. With the exception of
the initial wastewater characterization sampling frequency, the ERA was otherwise completed in
accordance with the Standard Method.
1.2 Background
The Canada-wide Strategy (CWS) for the Management of Municipal Wastewater Effluent was adopted
by the Canadian Council of Ministers of the Environment (CCME) in 2009. The Strategy is focused on
two main outcomes: Improved human health and environmental protection; and, improved clarity
about the way municipal wastewater effluent is managed and regulated. The Strategy requires that all
wastewater facilities discharging effluent to surface water meet the following National Performance
Standards (NPS) as a minimum:
• Carbonaceous Biochemical Oxygen Demand for five days (CBOD5) – 25 mg/L;
• Total Suspended Solids (TSS) – 25 mg/L; and
• Total Residual Chlorine (TRC) – 0.02 mg/L.
The Wastewater Systems Effluent Regulations (WSER) came into effect in 2012 under the Fisheries Act.
The WSER include the above NPS as well as the following criteria:
• Unionized ammonia – 1.25 mg/L, expressed as nitrogen (N), at 15°C ± 1°C.
The CWS requires that facilities develop site-specific Effluent Discharge Objectives (EDOs) to address
substances not included in the NPS that are present in the effluent. EDOs are the substance
concentrations that can be discharged in the effluent and still provide adequate protection of human
health and the environment. They are established by conducting a site-specific ERA. The ERA includes
characterization of the effluent to determine substances of concern, and characterization of the
Harbour Engineering Joint Venture Donkin WWTP ERA 2
receiving water to determine beneficial water uses, ambient water quality, assimilative capacity, and
available dilution. A compliance monitoring program is then developed and implemented to ensure
adherence to the established EDOs for the facility.
1.3 Facility Description
The proposed Donkin Wastewater Treatment Plant (WWTP) will be constructed adjacent to Bastable
Street. Treated effluent will be discharged to the Atlantic Ocean at the location of the existing
outfall in Borden’s Cove as indicated on Figure 1.2. The service population of Donkin is 471 people
in 256 residential units, based on 2016 census data.
Figure 1.1 Site Location
Harbour Engineering Joint Venture Donkin WWTP ERA 3
Figure 1.2 WWTP Location
The theoretical domestic wastewater flow is an average of 160 m3/day with a peak of 640 m3/day
based on a per capita flow of 340 L/person/day and a peaking factor of 4 calculated using the
Harmon formula. The sewer system was flow metered from March 13 to May 1, 2018. The meter
location is just upstream of the discharge and encompasses the entire wastewater system. The
average dry weather flow was 200 m3/day (425 L/p/d or 93 IG/p/d). The average daily flow during
the metering period was 466 m3/day (989 L/p/d or 218 IG/p/d). The maximum daily flow during the
metering period was 4781 m3/day. This occurred during a large rain event (50.8mm according to
Sydney A rain gauge, or 79.1mm according to Sydney CS rain gauge).
For the purposes of this ERA, the average daily flow for the metering period of 466 m3/day will be
used. However, this flow is likely higher than the average annual flow as the flow was only metered
for seven weeks, which occurred during a wet period: March and April 2018. It also included flow
data from the April 28 rain event, which was significant. If this rain event was omitted, the average
flow during the metering period would be 300 m3/day. As the population in this area is declining,
accounting for a projected population increase during the life of the plant was not necessary.
The preliminary design of the WWTP was completed based on a design average daily flow of 360
m3/d and a maximum month flow of 400 m3/day. As these values are less than the flowrate initially
used in the ERA, the ERA modelling will not be revised based on the design numbers.
Harbour Engineering Joint Venture Donkin WWTP ERA 4
CHAPTER 2 INITIAL WASTEWATER CHARACTERIZATION
2.1 Substances of Potential Concern
An initial characterization program covering a one-year period is typically required by the Standard
Method to describe the effluent and identify substances of concern. As there is no existing WWTP
for this system, and the ERA is being conducted for the purpose of determining effluent objectives
for the design of a new WWTP, only one sample event was completed of the untreated wastewater.
Sample results of the untreated wastewater were also available for some of the parameters of
potential concern from three-years of monthly sampling conducted by CBRM from 2015 through
2017. Substances of potential concern are listed in the Standard Method based on the size category
of the facility. The proposed design capacity of the new WWTP will be finalized during the pre-
design study, but for the purposes of the ERA, the average daily flow during the metering period of
466 m3/day will be used. As discussed previously, the actual average annual daily flow is expected
to be lower than this. Therefore, the WWTP is classified as a “very small” facility based on an
average daily flow rate that is less than or equal to 500 m3/day.
The substances of potential concern for a “very small” facility, as per the Standard Method, are detailed
in Table 2.1. There were no additional substances of potential concern identified to be monitored as
there is no industrial input to the wastewater system.
Table 2.1 Substances of Potential Concern for a Very Small Facility
Substance Group Substances
General Chemistry/ Nutrients
Total Suspended Solids (TSS)
Carbonaceous Biochemical Oxygen Demand (CBOD5)
Total Residual Chlorine (TRC) if chlorination is used
Total Ammonia Nitrogen
Total Kjeldahl Nitrogen (TKN)
Total Phosphorus (TP)
pH
Temperature
Pathogens E. coli
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2.1.1 Whole Effluent Toxicity
Wastewater effluent potentially contains a variety of unknown or unidentified substances for which
guidelines do not exist. In order to adequately protect against these unknown substances, Whole
Effluent Toxicity (WET) tests are typically conducted to evaluate acute (short-term) and chronic (long-
term) effects.
The Standard Method requires the following toxicity tests be conducted quarterly:
• Acute toxicity – Rainbow Trout and Daphnia Magna; and
• Chronic Toxicity – Ceriodaphnia Dubia and Fathead Minnow.
A draft for discussion, Mixing Zone Assessment and Report Template, dated July 6, 2016 that was
prepared by a committee of representatives of the environment departments in Atlantic Canada noted
that only Ceriodaphnia dubia testing is required for chronic toxicity. If the test does not pass, a fathead
minnow test is required.
As the wastewater in this system is currently untreated, and the purpose of the ERA is to determine
effluent discharge objectives for the design of a new WWTP, no WET tests were conducted at this time.
2.2 Wastewater Characterization Results
The results of the initial untreated wastewater characterization sample collected by Harbour
Engineering (HE) is provided in Table 2.2. A summary of the results of the untreated wastewater
characterization samples collected by CBRM from 2015 through 2017 are summarized in Table 2.3.
Table 2.2 Initial Wastewater Characterization Results
Parameter Units 24-Apr-18
CBOD5 mg/L 90
Total Kjeldahl Nitrogen (TKN) mg/L 9.7
Nitrogen (Ammonia Nitrogen) as N mg/L 2.9
Unionized ammonia(1) mg/L 0.0096
pH pH 7.08
Total Phosphorus mg/L 1.5
Total Suspended Solids mg/L 50
E. coli MPN/ 100mL >240,000
Total Coliforms MPN/ 100mL >240,000
Note: (1) The value of unionized ammonia was determined in accordance with the formula in the WSER, the
concentration of total ammonia in the sample, and the pH of the sample.
Harbour Engineering Joint Venture Donkin WWTP ERA 6
Table 2.3 CBRM Wastewater Characterization Samples
Parameter Units Average Maximum Number of Samples
CBOD5 mg/L 111.2 370 36
Nitrogen (Ammonia Nitrogen) as N mg/L 5.3 8.4 11
Unionized Ammonia mg/L 0.008 0.014 11
pH units 6.7 7 11
Total Suspended Solids mg/L 273.5 4100 36
As mentioned previously, although the frequency of testing specified by the Standard Method was
not met, the ERA will be completed with the available data.
Harbour Engineering Joint Venture Donkin WWTP ERA 7
CHAPTER 3 ENVIRONMENTAL QUALITY OBJECTIVES
Generic Environmental Quality Objectives (EQOs) are generated from established guidelines, typically
the Wastewater Systems Effluent Regulations (WSER), the Canadian Environmental Quality Guidelines
(CEQGs) and other guidelines specified by jurisdiction. Site-specific EQOs are established by adjusting
the generic EQOs based on site-specific factors, particularly ambient water quality. For example, if the
background concentration of a substance is greater than the guideline value (generic EQO), the
background concentration is used as the site-specific EQO. However, substances where the EQO is
based on the WSER are not adjusted based on ambient water quality. Furthermore, there are some
guidelines that are dependent on characteristics of the receiving water like pH or temperature. Effluent
is required to be non-acutely toxic at the end of pipe and non-chronically toxic at the edge of the mixing
zone.
EQOs can be determined by three different approaches:
• Physical/chemical/pathogenic – describes the substance levels that will protect water quality;
• Whole Effluent Toxicity (WET) – describes the proportion of effluent that can enter the receiving
water without causing toxicological effects (both acute and chronic); and
• Biological criteria (bio-assessment) – describes the level of ecological integrity that must be
maintained.
This assessment follows the physical/chemical/pathogenic approach from the Standard Method
outlined in the CCME guidelines. The bio-assessment is not included in the Standard Method as it is still
being developed (CCME, 2008).
3.1 Water Uses
EQOs are numerical values and narrative statements established to protect the receiving water – in this
case, Borden’s Cove in the Atlantic Ocean. The first step in determining EQOs is to define the potential
beneficial uses of the receiving water.
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The following beneficial water uses have been identified for the Atlantic Ocean in the vicinity of Donkin:
• Direct contact recreational activities like swimming and wading at the beach in nearby Schooner
Pond (approximately 1.2km away), shown on Figure 3.1;
• Secondary contact recreational activities like boating and fishing; and
• Ecosystem health for fisheries and marine aquatic life.
There is no molluscan shellfish harvesting zone in the vicinity of the outfall. The outfall is situated in
a molluscan shellfish closure zone boundary extending from Point Aconi to Schooner Pond
(approximately 720m from the discharge). The closure zone boundary is shown on Figure 3.1.
Figure 3.1 Location of Outfall
3.2 Ambient Water Quality
Generic EQOs are first developed based on existing guidelines and then adjusted based on site-
specific factors, particularly background water quality. Water quality data was obtained for two
locations in the Atlantic Ocean along the coast of Cape Breton. The locations were chosen in an
attempt to be representative of ambient water quality outside the influence of the existing
untreated wastewater discharges in CBRM. Samples were collected by HE on May 11, 2018, and the
sample locations are summarized as follows and presented in Figure 3.2:
• BG-1: Near Mira Gut Beach.
• BG-2: Wadden’s Cove.
Harbour Engineering Joint Venture Donkin WWTP ERA 9
Figure 3.2 Ambient Water Quality Sample Locations
A third sample was collected north of Port Morien but the results were not considered
representative of background conditions as sample results indicated the sample was impacted by
wastewater. Samples were collected as grab samples from near shore using a sampling rod. A
summary of the ambient water quality data is shown in Table 3.1.
Table 3.1 Ambient Water Quality Data
Parameter Units BG1 BG2 AVG
Carbonaceous BOD (CBOD) mg/L <5.0 <5.0 <5.0
Total Kjeldahl Nitrogen (TKN) mg/L 0.19 0.20 0.20
Nitrogen (Ammonia Nitrogen) mg/L <0.050 <0.050 <0.05
unionized ammonia mg/L <0.0007 <0.0007 <0.0007
pH pH 7.73 7.68 7.71
Total Phosphorus (TP) mg/L 0.037 0.032 0.035
TRC(1) mg/L NM NM NM
TSS mg/L 58 5.0 32
E. coli MPN/100mL 52 86 69
Total Coliforms MPN/100mL 16000 6900 11450
Note:
(1) NM = Parameter not measured.
Harbour Engineering Joint Venture Donkin WWTP ERA 10
3.3 Physical/ Chemical/ Pathogenic Approach
The physical/chemical/pathogenic approach is intended to protect the receiving water by ensuring that
water quality guidelines for particular substances are being met. EQOs are established by specifying the
level of a particular substance that will protect water quality. Substance levels that will protect water
quality are taken from the CEQGs associated with the identified beneficial water uses. If more than one
guideline applies, the most stringent is used. Typically the Canadian Water Quality Guidelines (CWQGs)
for the Protection of Aquatic Life are the most stringent and have been used for this assessment. The
Guidelines for Canadian Recreational Water have also been used to provide limits for pathogens
(E. coli).
The guidelines for the Protection of Aquatic Life provide recommendations for both freshwater and
marine (including estuarine) environments. Since the receiving water for the proposed Donkin WWTP is
a marine environment, the marine guidelines were used, where available.
Site-specific EQOs are derived in the following sections for each substance of potential concern.
3.3.1 General Chemistry/ Nutrients
The following general chemistry and nutrients parameters were identified as substances of potential
concern for a very small facility: CBOD, un-ionized ammonia, total ammonia, total nitrogen, total
Kjeldahl nitrogen (TKN), total suspended solids (TSS), total phosphorus, pH, and total residual
chlorine (TRC). EQOs for these substances are established in the following sections.
Oxygen Demand
Biochemical Oxygen Demand (BOD5) is a measure of the oxygen required to oxidize organic material
and certain inorganic materials over a given period of time (five days). It has two components:
carbonaceous oxygen demand and nitrogenous oxygen demand.
Carbonaceous Biochemical Oxygen Demand (CBOD5) measures the amount of biodegradable
carbonaceous material in the effluent that will require oxygen to break down over a given period of
time (five days). The CBOD5 discharged in wastewater effluent reduces the amount of dissolved
oxygen in the receiving water. Dissolved oxygen is an essential parameter for the protection of
aquatic life; and the higher the CBOD5 concentration, the less oxygen that is available for aquatic
life.
Traditionally performance standards have been set for BOD5; however, the WSER dictate a limit for
CBOD5. This is due to the variable effects of nitrogenous oxygen demand on the BOD5 test.
There are no CWQGs for the protection of aquatic life for CBOD5 in freshwater or in marine waters.
However, because CBOD5 affects the concentration of dissolved oxygen, the CWQG for dissolved
oxygen should be considered. The CWQG for freshwater aquatic life dictates that the dissolved
oxygen concentrations be greater than 9.5 mg/L for early life stages in cold water ecosystems. The
CWQG for marine aquatic life is a minimum of 8 mg/L.
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The background dissolved oxygen concentrations were not measured in the receiving water.
However, the concentration of CBOD5 discharged in accordance with the WSER criteria should not
cause the dissolved oxygen (DO) concentration to vary outside of the normal range. Based on an
average annual temperature of 6.9 °C (from Bedford Institute of Oceanography Area 4VN), the
solubility of oxygen in seawater is approximately 9.5 mg/L. Assuming the background concentration
of DO is saturated, there can be a drop of 1.5 mg/L for the DO to be a minimum concentration of 8
mg/L. For an ocean discharge, the maximum DO deficit should occur at the point source.
Assuming a deoxygenation rate of 0.33/day based on a depth of approximately 2m at the discharge
location, and assuming a reaeration coefficient of 0.61/day based on a depth of approximately 2m
and an average tidal velocity of 0.112 m/s. The maximum concentration of CBOD that would result
in a drop in DO of 1.5 mg/L can be calculated. The tidal dispersion coefficient has been assumed to
be 150 m2/s. The concentration of CBOD potentially affecting DO was calculated to be 23.7 mg/L.
Therefore, the WSER criteria of 25 mg/L CBOD at discharge should not cause the dissolved oxygen
(DO) concentration to vary outside of the normal range as initial dilution would result in a
concentration much lower than 23.7 mg/L CBOD. The background level of CBOD was less than the
detection limit of 5 mg/L.
Total Ammonia and Un-ionized Ammonia
The CWQG for the protection of aquatic life for total ammonia in freshwater is presented as a table
based on pH and temperature. There is no CWQG for ammonia in marine water. Total ammonia is
comprised of un-ionized ammonia (NH3) and ionized ammonia (NH4+, ammonium). Un-ionized
ammonia is more toxic than ionized ammonia and the toxicity of total ammonia is related to the
concentration of un-ionized ammonia present. The amount of un-ionized ammonia is variable
depending on pH and temperature, which is why the total ammonia guideline is given by pH and
temperature. Table 3.2 shows the CWQGs for total ammonia, as reproduced from the guidelines.
Table 3.2 CWQG for Total Ammonia (mg/L NH3) for the Protection of Aquatic Life
(freshwater)
Temp (˚C) pH
6.0 6.5 7.0 7.5 8.0 8.5 9.0 10
0 231 73.0 23.1 7.32 2.33 0.749 0.250 0.042
5 153 48.3 15.3 4.84 1.54 0.502 0.172 0.034
10 102 32.4 10.3 3.26 1.04 0.343 0.121 0.029
15 69.7 22.0 6.98 2.22 0.715 0.239 0.089 0.026
20 48.0 15.2 4.82 1.54 0.499 0.171 0.067 0.024
25 33.5 10.6 3.37 1.08 0.354 0.125 0.053 0.022
30 23.7 7.5 2.39 0.767 0.256 0.094 0.043 0.021
Notes:
• It is recommended in the guidelines that the most conservative value be used for the pH and temperature
closest to the measured conditions (e.g., the guideline for total ammonia at a temperature of 6.9˚C and pH of 7.9
would be 1.04 mg/L);
• According to the guideline, values falling outside of shaded area should be used with caution; and
• Values in the table are for Total Ammonia (NH3); they can be converted to Total Ammonia Nitrogen (N) by
multiplying by 0.8224.
Harbour Engineering Joint Venture Donkin WWTP ERA 12
The CWQG for total ammonia in freshwater is 0.499 mg/L or 0.41 mg/L NH3 as nitrogen, which is
based on an average background pH of 7.7 and a maximum monthly average temperature of 17.7
°C. The USEPA saltwater guideline for total ammonia is 2.7 mg/L based on a temperature of 17.7 °C,
a pH of 7.7 and a salinity of 30 g/kg. The USEPA guideline of 2.7 mg/L will be used as the EQO for
total ammonia. As ammonia is a component of total nitrogen (TN), the actual effluent
concentration may be limited by the TN EDO rather than the total ammonia EDO. However, as the
TN EQO is based on concern of eutrophication and not a continuous acceptable concentration for
the protection of aquatic life, both EDOs will be presented separately in the ERA.
The WSER requires that un-ionized ammonia concentrations be less than 1.25 mg/L at the discharge
point. For the purposes of this study, the EQO for un-ionized ammonia was chosen based on the
WSER (1.25 mg/L at discharge).
Total Suspended Solids (TSS)
The WSER specifies a limit of 25 mg/L for TSS at the end of the pipe. The CWQG for the protection of
aquatic life in marine water for total suspended solids (TSS) is as follows:
• During periods of clear flow, a maximum increase of 25 mg/L from background levels for any
short-term exposure (e.g., 24-h period). Maximum average increase of 5 mg/L from
background levels for longer term exposures (e.g., inputs lasting between 24 h and 30 d).
• During periods of high flow, a maximum increase of 25 mg/L from background levels at any
time when background levels are between 25 and 250 mg/L. Should not increase more than
10% of background levels when background is ≥ 250 mg/L.
The background concentration of TSS was an average of 32 mg/L. A maximum average increase of
5mg/L from background levels would result in an EQO of 37 mg/L. As this is greater than the WSER
criteria, the WSER criteria of 25 mg/L at discharge will apply as the EDO. The background TSS
measurement is higher than would typically be expected in a marine environment, which may be
due to the near shore location of the samples. However, in a worst case scenario where the
background TSS concentration was 0 mg/L, application of the WSER criteria at the end of pipe would
always be the more stringent criteria provided there is greater than five times dilution.
Total Phosphorus and TKN
There are no CWQGs for the protection of aquatic life for phosphorus or Total Kjeldahl Nitrogen.
However, in both freshwater and marine environments, adverse secondary effects like
eutrophication and oxygen depletion can occur. Guidance frameworks have been established for
freshwater systems and for marine systems to provide an approach for developing site-specific
water quality guidelines. These approaches are based on determining a baseline condition and
evaluating various effects according to indicator variables. The approach is generally very time and
resource intensive, but can be completed on a more limited scale to establish interim guidelines.
The Canadian Guidance Framework for the Management of Nutrients in Nearshore Marine Systems
Scientific Supporting Document (CCME, 2007) provides a framework as well as case studies for
establishing nutrient criteria for nearshore marine systems. This document provides a Trophic Index
for Marine Systems (TRIX), below.
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Table 3.3 Criteria for evaluating trophic status of marine systems (CCME, 2007)
Trophic Status TN
(mg/m3)
TP
(mg/m3) Chlorophyll a (μg/L) Secchi Depth
(m)
Oligotrophic <260 <10 <1 >6
Mesotrophic ≥260-350 ≥10-30 ≥1-3 3-≤6
Eutrophic ≥350-400 ≥30-40 ≥3-5 1.5-≤3
Hypereutrophic >400 >40 >5 <1.5
The background concentrations of TKN and TP were measured as 0.2 mg/L and 0.035 mg/L,
respectively, which corresponds to a eutrophic status based on the phosphorus concentration. The
uppermost limit for this trophic status is a TN concentration of 0.4 mg/L and a TP concentration of
0.04 mg/L.
This document provides another index (NOAA) to determine the degree of eutrophication of the
marine system, below.
Table 3.4 Trophic status classification based on nutrient and chlorophyll (CCME, 2007)
Degree of
Eutrophication
Total Dissolved N
(mg/L)
Total Dissolved P
(mg/L)
Chl a
(μg/L)
Low 0 - ≤0.1 0 - ≤0.01 0 - ≤5
Medium >0.1 - ≤1 >0.01 - ≤0.1 >5 - ≤20
High >1 >0.1 >20 - ≤60
Hypereutrophic - - >60
However, the concentrations in Table 3.4 are based on dissolved nitrogen and phosphorus and the
background concentrations are for TKN and total phosphorus. For nitrogen, with a background
concentration of 0.2 mg/L for TKN, an assumption that the dissolved nitrogen background
concentration is anywhere between 50 and 100% of the TKN background concentration would result
in classification as “medium” based on Table 3.4. For phosphorus, with a background concentration
of 0.035 mg/L, an assumption that the dissolved background concentration is anywhere between 29
and 100% of the total background concentration would result in classification as “medium” based on
Table 3.4.
To maintain the same degree of eutrophication, the total dissolved nitrogen and total dissolved
phosphorus in the receiving water should not exceed the upper limit of the “medium” classification
which is 1 mg/L for Total Dissolved Nitrogen and 0.1 mg/L for Total Dissolved Phosphorus. In
order to determine the upper limit of the “medium” eutrophication range based on total
phosphorus and TN concentrations, an assumption must be made as to the percentage of the
nitrogen and phosphorus that exists in the dissolved phase, both in the receiving water and in the
effluent. As a measure of conservatism, an assumption was made that 100% of the total nitrogen
and phosphorus exist in a dissolved phase. This allows for the upper limits of the “medium”
classification to be used directly as the EQO which results in an EQO of 1 mg/L for TN and 0.1 mg/L
for total phosphorus.
Harbour Engineering Joint Venture Donkin WWTP ERA 14
The Canadian Guidance Framework for the Management of Nutrients in Nearshore Marine Systems
Scientific Supporting Document (CCME, 2007) presents both of the above criteria for assessing
trophic status and does not provide a recommendation for use of one rather than the other.
However, the framework presents a case study to establish nutrient criteria for the Atlantic
Shoreline of Nova Scotia, and the NOAA index is used. Therefore, that index will be used for the
purpose of this study.
pH
The CWQG for the protection for aquatic life for marine waters is 7.0 to 8.7. This pH range will be
applied as the EQO.
Total Residual Chlorine
The WSER requires that TRC concentrations be less than 0.02 mg/L. For the purposes of this study,
the EQO/EDO of 0.02 mg/L for TRC was chosen based on this regulation.
3.3.2 E. coli
Pathogens are not included in the CCME WQGs for the protection of aquatic life. The Health Canada
Guidelines for Canadian Recreational Water Quality specify a maximum E. coli concentration of
200 E. coli/100 mL for freshwater for primary contact recreation and 1000 E. coli/100 mL for
secondary contact recreation. The Health Canada guideline for Canadian Recreational Water Quality
for primary and secondary contact recreation in marine water is based on enterococci rather than E.
coli. However, historical Nova Scotia Environment has set discharge limits for E. coli rather than
enterococci for marine discharges. The background concentration of E. coli was 69 E. coli/100 mL.
An EQO of 200 E. coli/ 100mL will apply for primary contact recreation at the beach in Schooner
Pond Cove. An EQO of 1000 E. coli/ 100mL based on the Canadian Recreational Water Quality
guideline for secondary contact for freshwater will apply elsewhere in the receiving water.
3.3.3 Summary
Table 3.5 below gives a summary of the generic and site-specific EQOs determined for parameters of
concern. The source of the EQO has been included in the table as follows:
• WSER – wastewater systems effluent regulations;
• Background – Site-specific EQO based on background concentration in receiving water;
• CWQG Marine – CCME Canadian Water Quality Guidelines for the Protection of Aquatic Life
Marine;
• USEPA Saltwater – United States Environmental Protection Agency National Recommended
Water Quality Criteria – Aquatic Life Criteria – Saltwater Criterion Continuous Concentration;
• CGF, Marine – Canadian Guidance Framework for the Management of Nutrients in Nearshore
Marine Systems Scientific Supporting Document;
• HC Primary Contact – Health Canada Guidelines for Canadian Recreational Water Quality –
Primary Contact Recreation; and
• HC Secondary Contact – Health Canada Guidelines for Canadian Recreational Water Quality –
Secondary Contact Recreation.
Harbour Engineering Joint Venture Donkin WWTP ERA 15
Table 3.5 EQO Summary
Parameter Generic EQO Background Selected EQO Source
CBOD5(1) (mg/) 25 <5.0 25 WSER
TN (mg/L) 1 0.2 1 CGF, Marine
Total NH3-N (mg/L) 2.7 <0.05 2.7 USEPA Saltwater
Un-ionized NH3-N(1) (mg/L) 1.25 <0.0007 1.25 WSER
pH 7.0 – 8.7 7.71 7.0 – 8.7 CWQG Marine
TP (mg/L) 0.1 0.035 0.1 CGF, Marine
TRC(1) (mg/L) 0.02 NM 0.02 WSER
TSS(1) (mg/L) 25 32 25 WSER
E. coli (MPN/ 100mL) 200 69 200 HC Primary Contact
E. coli (MPN/ 100mL) 1000 69 1000 HC Secondary Contact
Notes:
Bold indicates EQO is a WSER requirement.
(1) EQO applies at the end of pipe.
(2) Although the EQO for ammonia has been calculated to be 2.7 mg/L, an EQO of 1 mg/L for total nitrogen would govern.
However, as the EQO for TN is based on eutrophication, EDOs will be developed for all parameters separately.
Harbour Engineering Joint Venture Donkin WWTP ERA 16
CHAPTER 4 MIXING ZONE ANALYSIS
4.1 Methodology
4.1.1 Definition of Mixing Zone
A mixing zone is the portion of the receiving water where effluent dilution occurs. In general, the
receiving water as a whole will not be exposed to the immediate effluent concentration at the end-
of-pipe but to the effluent mixed and diluted with the receiving water. Effluent does not
instantaneously mix with the receiving water at the point of discharge. Depending on conditions
like ambient currents, wind speeds, tidal stage, and wave action, mixing can take place over a large
area – up to the point where there is no measureable difference between the receiving water and
the effluent mixed with receiving water.
The mixing process can be characterized into two distinct phases: near-field and far-field. Near-
field mixing occurs at the outfall and is influenced by the configuration of the outfall (e.g. pipe size,
diffusers, etc.). Far-field mixing is influenced by receiving water characteristics like turbulence, wave
action, and stratification of the water column.
Within the mixing zone, EQOs may be exceeded but acutely toxic conditions are not permitted
unless it is determined that un-ionized ammonia is the cause of toxicity. If the un-ionized ammonia
concentration is the cause of toxicity, there may be an exception (under the WSER) if the
concentration of un-ionized ammonia is less than or equal to 0.016 mg/L, expressed as N, at any
point that is 100 m from the discharge point. Outside of the mixing zone, EQOs must be achieved.
The effluent is also required to be non-chronically toxic outside of the mixing zone. The allocation of
a mixing zone varies from one substance to another – degradable substances are allowed to mix in a
portion of the receiving water whereas toxic, persistent, and bio-accumulative substances (such as
chlorinated dioxins and furans, PCBs, mercury, and toxaphene) are not allowed a mixing zone.
A number of general criteria for allocating a mixing zone are recommended in the Strategy, including the
following:
• The dimensions of a mixing zone should be restricted to avoid adverse effects on the designated
uses of the receiving water system (i.e., the mixing zone should be as small as possible);
• Conditions outside of the mixing zone should be sufficient to support all of the designated uses
of the receiving water system;
Harbour Engineering Joint Venture Donkin WWTP ERA 17
• A zone of passage for mobile aquatic organisms must be maintained;
• Placement of mixing zones must not block migration into tributaries;
• Changes to the nutrient status of the water body as a result of an effluent discharge should be
avoided; eutrophication or toxic blooms of algae are unacceptable impacts;
• Mixing zones for adjacent wastewater discharges should not overlap; and
• Adverse effects on the aesthetic qualities of the receiving water system (e.g. odour, colour,
scum, oil, floating debris) should be avoided (CCME, 1996).
The limits of the mixing zone may be defined for the following three categories of aquatic
environments based on their physical characteristics:
• streams and rivers;
• lakes, reservoirs and enclosed bays; and
• estuarine and marine waters.
Where several limits are in place, the first one to be reached sets the maximum extent of the mixing
zone allowed for the dilution assessment. Nutrients and fecal coliforms are not allocated any
maximum dilution. For fecal coliforms, the location of the water use must be considered and
protected by the limits of the mixing zone.
Based on these general guidelines, mixing zone extents must be defined on a case-by-case basis that
account for local conditions. It may also be based on arbitrary mixing zone limits for open water
discharges, e.g. a 100 m(1) or 250 m(2) radius from the outfall and/or a dilution limit. A Draft for
Discussion document “Mixing Zone Assessment and Report Templates” dated July 7, 2016, prepared
by a committee of representatives of the environment departments in Atlantic Canada, provides
guidance regarding mixing zones for ERAs in the Atlantic Provinces. This document recommends
that for ocean and estuary receiving waters a maximum dilution limit of 1:1000 be applied for far-
field mixing.
Finally, the assessment shall be based on ‘critical conditions’. For example, in the case of a river
discharge (not applicable here), ‘critical conditions’ can be defined as the seven-day average low
river flow for a given return period. The Standard Method provides the following guidance on EDO
development:
“…reasonable and realistic but yet protective scenarios should be used. The objective is to simulate
the critical conditions of the receiving water, where critical conditions are where the risk that the
effluent will have an effect on the receiving environment is the highest – it does not mean using the
highest effluent flow, the lowest river flow, and the highest background concentration
simultaneously.”
1 Environment Canada, 2006 - Atlantic Canada Wastewater Guidelines Manual for Collection, Treatment, and Disposal
2 NB Department of Environment & Local Government, 2012 Memo.
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As the critical low flow condition is used for the receiving water, the WWTP effluent will be
modelled based on an annual average flow, rather than a maximum daily or hourly flow, as applying
a critical high flow condition for the effluent simultaneously with a critical low flow condition in the
receiving water would result in overly conservative EDOs as this scenario doesn’t provide a
reasonable or realistic representation of actual conditions.
4.1.2 Site Summary
The WWTP is assumed to discharge through an outfall pipe perpendicular to the shoreline in shallow
water, extended to a depth estimated at -1.0 m below low tide. The low tide and -1.0 m depth
contours were estimated based on navigation charts. The total average effluent discharge is
modeled as a continuous point source of 466 m3/day.
The major coastal hydrodynamic features of the area are as follows:
• Along-shore currents along the open coastline are in phase with the tide, i.e. the current
speed peaks at high and low tide; and
• At the outfall site, breaking waves and associated longshore currents will contribute to
effluent dispersion during storms. For this assessment, we have assumed calm summer
conditions (i.e. no waves), when effluent dilution would be at a minimum.
4.1.3 Far-Field Modeling Approach and Inputs
The local mixing zone is limited by the water depth at the outfall of approximately -1.0 m Chart
Datum and by the presence of the shoreline. Since the outfall is in very shallow water, the buoyant
plume will always reach the surface upon release from the outfall3. Far-field mixing will then be
determined by ambient currents, which is best simulated with a hydrodynamic and effluent
dispersion model.
We implemented a full hydrodynamic model of the receiving coastal waters using the Danish
Hydraulic Institute’s MIKE21 model. MIKE21 is ideally suited to the study of outfall discharges in
shallow coastal areas where complex tidal and wind-driven currents drive the dispersion process.
The model was developed using navigation charts, tidal elevations, and wind observations for the
area. A similar model had been used by CBCL for CBRM in the past:
• In 2005 for the assessment of the past wastewater contamination problem at Dominion
Beach, which led to the design of the WWTP at Dominion4; and
• In 2014 for ERAs at the Dominion and Battery Point WWTPs.
The hydrodynamic model was calibrated to the following bottom current meter data:
• 1992 current meters (4 locations) located in 10 m-depth for the study by ASA5 on local
oceanography and effluent dispersion; and
• 2006 current meters (2 locations) off the Donkin peninsula for the CBCL study of mine
effluent dispersion.
3 Fisher et al., 1979. Mixing in Inland and Coastal Waters. Academic Press, London.
4 CBCL Limited, 2005. Dominion Beach Sewer Study. Prepared for CBRM.
5 ASA Consulting Limited, 1994. “Industrial Cape Breton Receiving Water Study, Phase II”. Prepared for The Town of Glace
Bay.
Harbour Engineering Joint Venture Donkin WWTP ERA 19
Calibration consisted of adjusting the following parameters:
• Bottom friction; and
• Model spatial resolution in the area of the current meters.
Numerical Model Domain with Locations of Current Meter Observations and Modeled Outfall
Location are shown in Figure 4.1. Inputs and calibrated outputs are shown in Figure 4.2. The
modelled current magnitudes at New Waterford, Glace Bay, and Donkin are in relatively good
agreement with observations, which is satisfactory to assess the overall dilution patterns of effluent
from the outfall. The effect of waves was not included in the model, and therefore the modeled
effluent concentration near the outfall is expected to be conservatively high.
Figure 4.1 Numerical Model Domain with Locations of Current Meter Observations and
Modeled Outfall Location
Harbour Engineering Joint Venture Donkin WWTP ERA 20
Figure 4.2 Time-series of Hydrodynamic Model Inputs and Calibration Outputs
Harbour Engineering Joint Venture Donkin WWTP ERA 21
4.2 Modeled Effluent Dilution
Snapshots of typical modeled effluent dispersion patterns are shown on Figure 4.3. Statistics on
effluent concentrations were performed over the one-month model run, and over a running seven-
day averaging period. Composite images of maximum and average effluent concentrations are
shown on Figure 4.4.
Effluent concentration peaks at any given location are short-lived because the plume is changing
direction every few hours depending on tides and winds. Therefore, a representative dilution
criteria at the mixing zone limit is best calculated using an average value. We propose to use the
one-day average effluent concentration criteria over the one-month modeling simulation that
includes a representative combination of site-specific tides and winds.
The diluted effluent plume often reaches the shoreline 100 m to the West of the outfall as well as
the shoreline farther away to the south and the northwest at low concentrations. Maximum
concentrations 100 m away from the outfall are typically encountered to the South at low tide, and
to the North at high tide. The 100 m distance from the outfall to the shoreline is within the brackets
of mixing zone radiuses defined by various guidelines. We propose that this distance be used as
mixing zone limit.
The maximum daily average effluent concentration 100 m away from the outfall over the simulation
period is 0.165 % (Table 4.1). Therefore we propose that a 606:1 dilution factor be used for
calculating EDOs based on the maximum 1-day average effluent concentration at 100 m from the
discharge.
Table 4.1 Modelled Dilution Values 100 and 200 m away from the Outfall
Distance
away from
the outfall
Hourly maximum
effluent
concentration
Maximum 1-day
average effluent
concentration
Maximum 7-day
average effluent
concentration
1-Month average
effluent
concentration
100 m 1.567 % (64:1
Dilution)
0.165 % (606:1
Dilution)
0.138 % (725:1
Dilution)
0.105 % (952:1
Dilution)
200 m 0.362 % (276:1
Dilution)
0.080 % (1250:1
Dilution)
0.068 % (1471:1
Dilution)
0.035 % (2857:1
Dilution)
Harbour Engineering Joint Venture Donkin WWTP ERA 22
Figure 4.3 Snapshots of Typical Modeled Effluent Dispersion Patterns
Harbour Engineering Joint Venture Donkin WWTP ERA 23
Figure 4.4 Composite Images of Modeled Hourly Maximum (top) and Maximum 7-Day
Average Effluent Concentrations (middle) with Concentration Time-Series
(bottom)
Note: 100-m radius (black) and 200-m radius (grey) circle shown around outfall.
Harbour Engineering Joint Venture Donkin WWTP ERA 24
CHAPTER 5 EFFLUENT DISCHARGE OBJECTIVES
5.1 The Need for EDOs
Effluent Discharge Objectives (EDOs) represent the effluent substance concentrations that will protect
the receiving environment and its designated water uses. They describe the effluent quality necessary
to allow the EQOs to be met at the edge of the mixing zone. The EQOs are established in Chapter 3; see
Table 3.5 for summary of results.
EDOs should be calculated where reasonable potential of exceeding the EQOs at the edge of the mixing
zone has been determined. Typically, substances with reasonable potential of exceeding the EQOs have
been selected according to the simplified approach: If a sample result measured in the effluent exceeds
the EQO, an EDO is determined. As there are a limited number of parameters considered as substances
of potential concern for very small and small facilities, EDOs will be developed for all substances of
potential concern.
5.2 Physical/ Chemical/ Pathogenic EDOs
For this assessment, EDOs were calculated using the dilution values obtained at the average daily
flow of 466 m3/day that was measured during the metering period. This resulted in a dilution of
606:1 at the edge of a 100 m mixing zone. The model shows a dilution of 2000:1 at Schooner Pond
Beach based on the maximum hourly concentration.
Parameters for which there is a WSER criteria were not allowed any dilution and therefore the EDO
equals the WSER Criteria. The Standard Method does not allocate any maximum dilution for
nutrients and fecal coliforms. For nutrients, it recommends a case-by-case analysis. For fecal
coliforms, the location of the water use must be protected by the limits of the mixing zone.
The dilution values were used to obtain an EDO by back-calculating from the EQOs. When the
background concentration of a substance was less than the detection limit, the background
concentration was not included in the calculation of the EDO.
Harbour Engineering Joint Venture Donkin WWTP ERA 25
5.3 Effluent Discharge Objectives
Substances of concern for which an EDO was developed are listed in Table 5.1 below with the
associated EQO, maximum measured wastewater concentration, and the associated EDO.
Table 5.1 Effluent Discharge Objectives at Proposed Design Conditions
Parameter
Maximum
Wastewater
Concentration
Background Selected
EQO Source Dilution
Factor EDO
CBOD (mg/L) 1400 <5.0 25 WSER - 25
TN (mg/L) 9.7 0.2 1 CGF, Marine 606 488
Total NH3-N
(mg/L) 8.4 <0.05 2.7 USEPA Saltwater 606 1636
Unionized NH3
(mg/L) 0.014 0 1.25 WSER - 1.25
TP (mg/L) 1.5 0.03 0.1 CGF, Marine 606 40
TRC (mg/L) NM NM 0.02 WSER - 0.02
TSS (mg/L) 4100 31.5 25 WSER - 25
E. coli (MPN/
100mL) >240,000 69 200 HC Primary Contact 2000 262,069
E. coli (MPN/
100mL) >240,000 69 1000 HC Secondary Contact 606 564,255
Based on the EDOs calculated above, sample results for the following parameters exceeded the EDO
in at least one wastewater sample:
• CBOD5;
• TSS; and
• E. coli.
These parameters will meet the EDOs at the discharge of the new WWTP through treatment.
Harbour Engineering Joint Venture Donkin WWTP ERA 26
CHAPTER 6 COMPLIANCE MONITORING
The Standard Method utilizes the results of the ERA to recommend parameters for compliance
monitoring according to the following protocol:
• The WSER requirements for TSS, CBOD and unionized ammonia must be monitored to
ensure they are continuously being achieved. Minimum monitoring frequencies are
specified in the guidelines based on the size of the facility. Monitoring of these
substances cannot be reduced or eliminated;
• Nutrients, such as phosphorus and ammonia, and pathogens for which an EDO was
developed should be included in the monitoring program with the same sampling
frequency as TSS and CBOD5;
• For additional substances, the guidelines require that all substances with average effluent
values over 80% of the EDO be monitored;
• If monitoring results for the additional substances are consistently below 80% of the EDO,
the monitoring frequency can be reduced;
• If average monitoring results subsequently exceed 80% of the EDO, monitoring frequency
must return to the initial monitoring frequency; and
• If monitoring results are below 80% of the EDO for at least 20 consecutive samples spread
over a period of at least one-year, monitoring for that substance can be eliminated.
Although the Standard Method results in recommending parameters for compliance monitoring, the
provincial regulator ultimately stipulates the compliance monitoring requirements as part of the
Approvals to Operate. In New Brunswick, the New Brunswick Department of Environment and Local
Government has been using the results of the ERA to update the compliance monitoring program
listed in the Approval to operate when the existing Approvals expire. At this time, it is premature to
use the results of this ERA to provide recommendations on parameters to monitor for compliance,
as the purpose of this ERA was to provide design criteria for design of a new WWTP.
Harbour Engineering Joint Venture Donkin WWTP ERA 27
CHAPTER 7 REFERENCES
ASA Consulting Limited (1994). “Industrial Cape Breton Receiving Water Study, Phase II”. Prepared
for The Town of Glace Bay.
BC Ministry of Environment (2006). A Compendium of Working Water Quality Guidelines for
British Columbia. Retrieved from: http://www.env.gov.bc.ca/wat/wq/BCguidelines/working.html
CBCL Limited (2005). Dominion Beach Sewer Study. Prepared for CBRM.
CCME (2008). Technical Supplement 3. Canada-wide Strategy for the Management of Municipal
Wastewater Effluent. Standard Method and Contracting Provisions for the Environmental Risk
Assessment.
CCME (2007). Canadian Guidance Framework for the Management of Nutrients in Nearshore
Marine Systems Scientific Supporting Document.
CCME Canadian Environmental Quality Guidelines Summary Table. Water Quality Guidelines for the
Protection of Aquatic Life.
Environment Canada (2006). Atlantic Canada Wastewater Guidelines Manual for Collection,
Treatment and Disposal
Environment Canada (Environment Canada) (1999). Canadian Environmental Protection Act Priority
Substances List II – Supporting document for Ammonia in the Aquatic Environment. DRAFT –August
31, 1999.
Fisher et al. (1979). Mixing in Inland and Coastal Waters. Academic Press, London.
Fisheries Act. Wastewater Systems Effluent Regulations. SOR/2012-139.
Health Canada (2012). Guidelines for Canadian Recreational Water Quality. Retrieved from:
http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/guide_water-2012-guide_eau/index-eng.php
Mixing Zone Assessment and Report Template Draft only – For discussion (July 7, 2016)
NB Department of Environment & Local Government, (2012). Memo.
Harbour Engineering Joint Venture Donkin WWTP ERA 28
Thomann, Robert V. and Mueller, John A (1987). Principles of Surface Water Quality Modeling and
Control.
UMA (1994). Industrial Cape Breton Wastewater Characterization Program, Phase II.
USEPA. National Recommended Water Quality Criteria for Saltwater. Retrieved from:
http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm
Prepared by: Reviewed by:
Holly Sampson, M.A.Sc., P.Eng. Karen March, M.Sc.
Intermediate Chemical Engineer Environmental Scientist
Harbour Engineering Joint Venture Appendices
APPENDIX A
Laboratory Certificates
Harbour Engineering Joint Venture Appendices
APPENDIX C
Conceptual Plant Layouts
j o i n t v e n t u r e
C01
CONCEPT
DRAWING
j o i n t v e n t u r e
C02
CONCEPT
DRAWING
j o i n t v e n t u r e
C03
CONCEPT
DRAWING
HEJV Donkin Wastewater System Pre-Design Summary Report Appendices
APPENDIX C
Donkin Environmental Risk Assessment
182402.00 ● Report ● April 2020
Donkin Wastewater Treatment Plant
Environmental Risk Assessment
Final Report
Prepared by:
Prepared for:
March 2020
Final April 14, 2020 Darrin McLean Karen March Holly Sampson
Draft for Review June 27, 2018 Darrin McLean Karen March Holly Sampson
Issue or Revision Date Issued By: Reviewed By: Prepared By:
This document was prepared for the party indicated
herein. The material and information in the
document reflects HE’s opinion and best judgment
based on the information available at the time of
preparation. Any use of this document or reliance
on its content by third parties is the responsibility of
the third party. HE accepts no responsibility for
any damages suffered as a result of third party use
of this document.
182402.00
March 27, 2020
275 Charlotte Street
Sydney, Nova Scotia
Canada
B1P 1C6
Tel: 902-562-9880
Fax: 902-562-9890
_________________
182402 RE 001 FINAL WWTP ERA DONKINKM2.DOCX/mk
ED: 14/04/2020 15:01:00/PD: 14/04/2020 15:01:00
April 14, 2020
Matt Viva, P.Eng.
Manager Wastewater Operations
Cape Breton Regional Municipality (CBRM)
320 Esplanade,
Sydney, NS B1P 7B9
Dear Mr. Viva:
RE: Donkin Wastewater Treatment Plant ERA – Final Report
Enclosed, please find a copy of the Environmental Risk Assessment (ERA) Report
for the Donkin Wastewater Treatment Plant (WWTP).
The report outlines Environmental Quality Objectives (EQOs) for all parameters
of potential concern listed in the Standard Method for a “very small” facility.
Environmental Discharge Objectives (EDOs) were also calculated for all
parameters of potential concern.
If you have any questions or require clarification on the content presented in
the attached report, please do not hesitate to contact us.
Yours very truly,
Harbour Engineering
Prepared by: Reviewed by:
Holly Sampson, M.A.Sc., P.Eng. Karen March, M.Sc.
Intermediate Chemical Engineer Environmental Scientist
Direct: 902-539-1330 Phone: 902-450-4000
E-Mail: hsampson@cbcl.ca E-Mail: kmarch@dillon.ca
Project No: 182402.00
March 27, 2020
Harbour Engineering Joint Venture Donkin WWTP ERA i
Contents
CHAPTER 1 Background and Objectives ......................................................................................... 1
1.1 Introduction ........................................................................................................................ 1
1.2 Background ......................................................................................................................... 1
1.3 Facility Description .............................................................................................................. 2
CHAPTER 2 Initial Wastewater Characterization ............................................................................ 4
2.1 Substances of Potential Concern ........................................................................................ 4
2.1.1 Whole Effluent Toxicity ........................................................................................... 5
2.2 Wastewater Characterization Results ................................................................................ 5
CHAPTER 3 Environmental Quality Objectives ............................................................................... 7
3.1 Water Uses .......................................................................................................................... 7
3.2 Ambient Water Quality ....................................................................................................... 8
3.3 Physical/ Chemical/ Pathogenic Approach ....................................................................... 10
3.3.1 General Chemistry/ Nutrients .............................................................................. 10
3.3.2 E. coli ..................................................................................................................... 14
3.3.3 Summary ............................................................................................................... 14
CHAPTER 4 Mixing Zone Analysis ................................................................................................. 16
4.1 Methodology ..................................................................................................................... 16
4.1.1 Definition of Mixing Zone ..................................................................................... 16
4.1.2 Site Summary ........................................................................................................ 18
4.1.3 Far-Field Modeling Approach and Inputs ............................................................. 18
4.2 Modeled Effluent Dilution ................................................................................................ 21
CHAPTER 5 Effluent Discharge Objectives .................................................................................... 24
5.1 The Need for EDOs ............................................................................................................ 24
5.2 Physical/ Chemical/ Pathogenic EDOs .............................................................................. 24
5.3 Effluent Discharge Objectives ........................................................................................... 25
CHAPTER 6 Compliance Monitoring ............................................................................................. 26
CHAPTER 7 References ................................................................................................................ 27
Appendices
A Laboratory Certificates
Harbour Engineering Joint Venture Donkin WWTP ERA 1
CHAPTER 1 BACKGROUND AND OBJECTIVES
1.1 Introduction
Harbour Engineering (HE) was engaged by the Cape Breton Regional Municipality (CBRM) to complete
an Environmental Risk Assessment (ERA) for the proposed Donkin Wastewater Treatment Plant
(WWTP). As this is a proposed WWTP that has not yet been designed, this ERA was completed with the
objective that it serve as a tool to establish effluent criteria for the design of a new WWTP. For this
reason, the ERA was completed without the frequency of testing required by the Standard Method
outlined in Technical Supplement 3 of the Canada-wide Strategy for the Management of Municipal
Wastewater Effluent (Standard Method) for initial wastewater characterization. With the exception of
the initial wastewater characterization sampling frequency, the ERA was otherwise completed in
accordance with the Standard Method.
1.2 Background
The Canada-wide Strategy (CWS) for the Management of Municipal Wastewater Effluent was adopted
by the Canadian Council of Ministers of the Environment (CCME) in 2009. The Strategy is focused on
two main outcomes: Improved human health and environmental protection; and, improved clarity
about the way municipal wastewater effluent is managed and regulated. The Strategy requires that all
wastewater facilities discharging effluent to surface water meet the following National Performance
Standards (NPS) as a minimum:
• Carbonaceous Biochemical Oxygen Demand for five days (CBOD5) – 25 mg/L;
• Total Suspended Solids (TSS) – 25 mg/L; and
• Total Residual Chlorine (TRC) – 0.02 mg/L.
The Wastewater Systems Effluent Regulations (WSER) came into effect in 2012 under the Fisheries Act.
The WSER include the above NPS as well as the following criteria:
• Unionized ammonia – 1.25 mg/L, expressed as nitrogen (N), at 15°C ± 1°C.
The CWS requires that facilities develop site-specific Effluent Discharge Objectives (EDOs) to address
substances not included in the NPS that are present in the effluent. EDOs are the substance
concentrations that can be discharged in the effluent and still provide adequate protection of human
health and the environment. They are established by conducting a site-specific ERA. The ERA includes
characterization of the effluent to determine substances of concern, and characterization of the
Harbour Engineering Joint Venture Donkin WWTP ERA 2
receiving water to determine beneficial water uses, ambient water quality, assimilative capacity, and
available dilution. A compliance monitoring program is then developed and implemented to ensure
adherence to the established EDOs for the facility.
1.3 Facility Description
The proposed Donkin Wastewater Treatment Plant (WWTP) will be constructed adjacent to Bastable
Street. Treated effluent will be discharged to the Atlantic Ocean at the location of the existing
outfall in Borden’s Cove as indicated on Figure 1.2. The service population of Donkin is 471 people
in 256 residential units, based on 2016 census data.
Figure 1.1 Site Location
Harbour Engineering Joint Venture Donkin WWTP ERA 3
Figure 1.2 WWTP Location
The theoretical domestic wastewater flow is an average of 160 m3/day with a peak of 640 m3/day
based on a per capita flow of 340 L/person/day and a peaking factor of 4 calculated using the
Harmon formula. The sewer system was flow metered from March 13 to May 1, 2018. The meter
location is just upstream of the discharge and encompasses the entire wastewater system. The
average dry weather flow was 200 m3/day (425 L/p/d or 93 IG/p/d). The average daily flow during
the metering period was 466 m3/day (989 L/p/d or 218 IG/p/d). The maximum daily flow during the
metering period was 4781 m3/day. This occurred during a large rain event (50.8mm according to
Sydney A rain gauge, or 79.1mm according to Sydney CS rain gauge).
For the purposes of this ERA, the average daily flow for the metering period of 466 m3/day will be
used. However, this flow is likely higher than the average annual flow as the flow was only metered
for seven weeks, which occurred during a wet period: March and April 2018. It also included flow
data from the April 28 rain event, which was significant. If this rain event was omitted, the average
flow during the metering period would be 300 m3/day. As the population in this area is declining,
accounting for a projected population increase during the life of the plant was not necessary.
The preliminary design of the WWTP was completed based on a design average daily flow of 360
m3/d and a maximum month flow of 400 m3/day. As these values are less than the flowrate initially
used in the ERA, the ERA modelling will not be revised based on the design numbers.
Harbour Engineering Joint Venture Donkin WWTP ERA 4
CHAPTER 2 INITIAL WASTEWATER CHARACTERIZATION
2.1 Substances of Potential Concern
An initial characterization program covering a one-year period is typically required by the Standard
Method to describe the effluent and identify substances of concern. As there is no existing WWTP
for this system, and the ERA is being conducted for the purpose of determining effluent objectives
for the design of a new WWTP, only one sample event was completed of the untreated wastewater.
Sample results of the untreated wastewater were also available for some of the parameters of
potential concern from three-years of monthly sampling conducted by CBRM from 2015 through
2017. Substances of potential concern are listed in the Standard Method based on the size category
of the facility. The proposed design capacity of the new WWTP will be finalized during the pre-
design study, but for the purposes of the ERA, the average daily flow during the metering period of
466 m3/day will be used. As discussed previously, the actual average annual daily flow is expected
to be lower than this. Therefore, the WWTP is classified as a “very small” facility based on an
average daily flow rate that is less than or equal to 500 m3/day.
The substances of potential concern for a “very small” facility, as per the Standard Method, are detailed
in Table 2.1. There were no additional substances of potential concern identified to be monitored as
there is no industrial input to the wastewater system.
Table 2.1 Substances of Potential Concern for a Very Small Facility
Substance Group Substances
General Chemistry/ Nutrients
Total Suspended Solids (TSS)
Carbonaceous Biochemical Oxygen Demand (CBOD5)
Total Residual Chlorine (TRC) if chlorination is used
Total Ammonia Nitrogen
Total Kjeldahl Nitrogen (TKN)
Total Phosphorus (TP)
pH
Temperature
Pathogens E. coli
Harbour Engineering Joint Venture Donkin WWTP ERA 5
2.1.1 Whole Effluent Toxicity
Wastewater effluent potentially contains a variety of unknown or unidentified substances for which
guidelines do not exist. In order to adequately protect against these unknown substances, Whole
Effluent Toxicity (WET) tests are typically conducted to evaluate acute (short-term) and chronic (long-
term) effects.
The Standard Method requires the following toxicity tests be conducted quarterly:
• Acute toxicity – Rainbow Trout and Daphnia Magna; and
• Chronic Toxicity – Ceriodaphnia Dubia and Fathead Minnow.
A draft for discussion, Mixing Zone Assessment and Report Template, dated July 6, 2016 that was
prepared by a committee of representatives of the environment departments in Atlantic Canada noted
that only Ceriodaphnia dubia testing is required for chronic toxicity. If the test does not pass, a fathead
minnow test is required.
As the wastewater in this system is currently untreated, and the purpose of the ERA is to determine
effluent discharge objectives for the design of a new WWTP, no WET tests were conducted at this time.
2.2 Wastewater Characterization Results
The results of the initial untreated wastewater characterization sample collected by Harbour
Engineering (HE) is provided in Table 2.2. A summary of the results of the untreated wastewater
characterization samples collected by CBRM from 2015 through 2017 are summarized in Table 2.3.
Table 2.2 Initial Wastewater Characterization Results
Parameter Units 24-Apr-18
CBOD5 mg/L 90
Total Kjeldahl Nitrogen (TKN) mg/L 9.7
Nitrogen (Ammonia Nitrogen) as N mg/L 2.9
Unionized ammonia(1) mg/L 0.0096
pH pH 7.08
Total Phosphorus mg/L 1.5
Total Suspended Solids mg/L 50
E. coli MPN/ 100mL >240,000
Total Coliforms MPN/ 100mL >240,000
Note: (1) The value of unionized ammonia was determined in accordance with the formula in the WSER, the
concentration of total ammonia in the sample, and the pH of the sample.
Harbour Engineering Joint Venture Donkin WWTP ERA 6
Table 2.3 CBRM Wastewater Characterization Samples
Parameter Units Average Maximum Number of Samples
CBOD5 mg/L 111.2 370 36
Nitrogen (Ammonia Nitrogen) as N mg/L 5.3 8.4 11
Unionized Ammonia mg/L 0.008 0.014 11
pH units 6.7 7 11
Total Suspended Solids mg/L 273.5 4100 36
As mentioned previously, although the frequency of testing specified by the Standard Method was
not met, the ERA will be completed with the available data.
Harbour Engineering Joint Venture Donkin WWTP ERA 7
CHAPTER 3 ENVIRONMENTAL QUALITY OBJECTIVES
Generic Environmental Quality Objectives (EQOs) are generated from established guidelines, typically
the Wastewater Systems Effluent Regulations (WSER), the Canadian Environmental Quality Guidelines
(CEQGs) and other guidelines specified by jurisdiction. Site-specific EQOs are established by adjusting
the generic EQOs based on site-specific factors, particularly ambient water quality. For example, if the
background concentration of a substance is greater than the guideline value (generic EQO), the
background concentration is used as the site-specific EQO. However, substances where the EQO is
based on the WSER are not adjusted based on ambient water quality. Furthermore, there are some
guidelines that are dependent on characteristics of the receiving water like pH or temperature. Effluent
is required to be non-acutely toxic at the end of pipe and non-chronically toxic at the edge of the mixing
zone.
EQOs can be determined by three different approaches:
• Physical/chemical/pathogenic – describes the substance levels that will protect water quality;
• Whole Effluent Toxicity (WET) – describes the proportion of effluent that can enter the receiving
water without causing toxicological effects (both acute and chronic); and
• Biological criteria (bio-assessment) – describes the level of ecological integrity that must be
maintained.
This assessment follows the physical/chemical/pathogenic approach from the Standard Method
outlined in the CCME guidelines. The bio-assessment is not included in the Standard Method as it is still
being developed (CCME, 2008).
3.1 Water Uses
EQOs are numerical values and narrative statements established to protect the receiving water – in this
case, Borden’s Cove in the Atlantic Ocean. The first step in determining EQOs is to define the potential
beneficial uses of the receiving water.
Harbour Engineering Joint Venture Donkin WWTP ERA 8
The following beneficial water uses have been identified for the Atlantic Ocean in the vicinity of Donkin:
• Direct contact recreational activities like swimming and wading at the beach in nearby Schooner
Pond (approximately 1.2km away), shown on Figure 3.1;
• Secondary contact recreational activities like boating and fishing; and
• Ecosystem health for fisheries and marine aquatic life.
There is no molluscan shellfish harvesting zone in the vicinity of the outfall. The outfall is situated in
a molluscan shellfish closure zone boundary extending from Point Aconi to Schooner Pond
(approximately 720m from the discharge). The closure zone boundary is shown on Figure 3.1.
Figure 3.1 Location of Outfall
3.2 Ambient Water Quality
Generic EQOs are first developed based on existing guidelines and then adjusted based on site-
specific factors, particularly background water quality. Water quality data was obtained for two
locations in the Atlantic Ocean along the coast of Cape Breton. The locations were chosen in an
attempt to be representative of ambient water quality outside the influence of the existing
untreated wastewater discharges in CBRM. Samples were collected by HE on May 11, 2018, and the
sample locations are summarized as follows and presented in Figure 3.2:
• BG-1: Near Mira Gut Beach.
• BG-2: Wadden’s Cove.
Harbour Engineering Joint Venture Donkin WWTP ERA 9
Figure 3.2 Ambient Water Quality Sample Locations
A third sample was collected north of Port Morien but the results were not considered
representative of background conditions as sample results indicated the sample was impacted by
wastewater. Samples were collected as grab samples from near shore using a sampling rod. A
summary of the ambient water quality data is shown in Table 3.1.
Table 3.1 Ambient Water Quality Data
Parameter Units BG1 BG2 AVG
Carbonaceous BOD (CBOD) mg/L <5.0 <5.0 <5.0
Total Kjeldahl Nitrogen (TKN) mg/L 0.19 0.20 0.20
Nitrogen (Ammonia Nitrogen) mg/L <0.050 <0.050 <0.05
unionized ammonia mg/L <0.0007 <0.0007 <0.0007
pH pH 7.73 7.68 7.71
Total Phosphorus (TP) mg/L 0.037 0.032 0.035
TRC(1) mg/L NM NM NM
TSS mg/L 58 5.0 32
E. coli MPN/100mL 52 86 69
Total Coliforms MPN/100mL 16000 6900 11450
Note:
(1) NM = Parameter not measured.
Harbour Engineering Joint Venture Donkin WWTP ERA 10
3.3 Physical/ Chemical/ Pathogenic Approach
The physical/chemical/pathogenic approach is intended to protect the receiving water by ensuring that
water quality guidelines for particular substances are being met. EQOs are established by specifying the
level of a particular substance that will protect water quality. Substance levels that will protect water
quality are taken from the CEQGs associated with the identified beneficial water uses. If more than one
guideline applies, the most stringent is used. Typically the Canadian Water Quality Guidelines (CWQGs)
for the Protection of Aquatic Life are the most stringent and have been used for this assessment. The
Guidelines for Canadian Recreational Water have also been used to provide limits for pathogens
(E. coli).
The guidelines for the Protection of Aquatic Life provide recommendations for both freshwater and
marine (including estuarine) environments. Since the receiving water for the proposed Donkin WWTP is
a marine environment, the marine guidelines were used, where available.
Site-specific EQOs are derived in the following sections for each substance of potential concern.
3.3.1 General Chemistry/ Nutrients
The following general chemistry and nutrients parameters were identified as substances of potential
concern for a very small facility: CBOD, un-ionized ammonia, total ammonia, total nitrogen, total
Kjeldahl nitrogen (TKN), total suspended solids (TSS), total phosphorus, pH, and total residual
chlorine (TRC). EQOs for these substances are established in the following sections.
Oxygen Demand
Biochemical Oxygen Demand (BOD5) is a measure of the oxygen required to oxidize organic material
and certain inorganic materials over a given period of time (five days). It has two components:
carbonaceous oxygen demand and nitrogenous oxygen demand.
Carbonaceous Biochemical Oxygen Demand (CBOD5) measures the amount of biodegradable
carbonaceous material in the effluent that will require oxygen to break down over a given period of
time (five days). The CBOD5 discharged in wastewater effluent reduces the amount of dissolved
oxygen in the receiving water. Dissolved oxygen is an essential parameter for the protection of
aquatic life; and the higher the CBOD5 concentration, the less oxygen that is available for aquatic
life.
Traditionally performance standards have been set for BOD5; however, the WSER dictate a limit for
CBOD5. This is due to the variable effects of nitrogenous oxygen demand on the BOD5 test.
There are no CWQGs for the protection of aquatic life for CBOD5 in freshwater or in marine waters.
However, because CBOD5 affects the concentration of dissolved oxygen, the CWQG for dissolved
oxygen should be considered. The CWQG for freshwater aquatic life dictates that the dissolved
oxygen concentrations be greater than 9.5 mg/L for early life stages in cold water ecosystems. The
CWQG for marine aquatic life is a minimum of 8 mg/L.
Harbour Engineering Joint Venture Donkin WWTP ERA 11
The background dissolved oxygen concentrations were not measured in the receiving water.
However, the concentration of CBOD5 discharged in accordance with the WSER criteria should not
cause the dissolved oxygen (DO) concentration to vary outside of the normal range. Based on an
average annual temperature of 6.9 °C (from Bedford Institute of Oceanography Area 4VN), the
solubility of oxygen in seawater is approximately 9.5 mg/L. Assuming the background concentration
of DO is saturated, there can be a drop of 1.5 mg/L for the DO to be a minimum concentration of 8
mg/L. For an ocean discharge, the maximum DO deficit should occur at the point source.
Assuming a deoxygenation rate of 0.33/day based on a depth of approximately 2m at the discharge
location, and assuming a reaeration coefficient of 0.61/day based on a depth of approximately 2m
and an average tidal velocity of 0.112 m/s. The maximum concentration of CBOD that would result
in a drop in DO of 1.5 mg/L can be calculated. The tidal dispersion coefficient has been assumed to
be 150 m2/s. The concentration of CBOD potentially affecting DO was calculated to be 23.7 mg/L.
Therefore, the WSER criteria of 25 mg/L CBOD at discharge should not cause the dissolved oxygen
(DO) concentration to vary outside of the normal range as initial dilution would result in a
concentration much lower than 23.7 mg/L CBOD. The background level of CBOD was less than the
detection limit of 5 mg/L.
Total Ammonia and Un-ionized Ammonia
The CWQG for the protection of aquatic life for total ammonia in freshwater is presented as a table
based on pH and temperature. There is no CWQG for ammonia in marine water. Total ammonia is
comprised of un-ionized ammonia (NH3) and ionized ammonia (NH4+, ammonium). Un-ionized
ammonia is more toxic than ionized ammonia and the toxicity of total ammonia is related to the
concentration of un-ionized ammonia present. The amount of un-ionized ammonia is variable
depending on pH and temperature, which is why the total ammonia guideline is given by pH and
temperature. Table 3.2 shows the CWQGs for total ammonia, as reproduced from the guidelines.
Table 3.2 CWQG for Total Ammonia (mg/L NH3) for the Protection of Aquatic Life
(freshwater)
Temp (˚C) pH
6.0 6.5 7.0 7.5 8.0 8.5 9.0 10
0 231 73.0 23.1 7.32 2.33 0.749 0.250 0.042
5 153 48.3 15.3 4.84 1.54 0.502 0.172 0.034
10 102 32.4 10.3 3.26 1.04 0.343 0.121 0.029
15 69.7 22.0 6.98 2.22 0.715 0.239 0.089 0.026
20 48.0 15.2 4.82 1.54 0.499 0.171 0.067 0.024
25 33.5 10.6 3.37 1.08 0.354 0.125 0.053 0.022
30 23.7 7.5 2.39 0.767 0.256 0.094 0.043 0.021
Notes:
• It is recommended in the guidelines that the most conservative value be used for the pH and temperature
closest to the measured conditions (e.g., the guideline for total ammonia at a temperature of 6.9˚C and pH of 7.9
would be 1.04 mg/L);
• According to the guideline, values falling outside of shaded area should be used with caution; and
• Values in the table are for Total Ammonia (NH3); they can be converted to Total Ammonia Nitrogen (N) by
multiplying by 0.8224.
Harbour Engineering Joint Venture Donkin WWTP ERA 12
The CWQG for total ammonia in freshwater is 0.499 mg/L or 0.41 mg/L NH3 as nitrogen, which is
based on an average background pH of 7.7 and a maximum monthly average temperature of 17.7
°C. The USEPA saltwater guideline for total ammonia is 2.7 mg/L based on a temperature of 17.7 °C,
a pH of 7.7 and a salinity of 30 g/kg. The USEPA guideline of 2.7 mg/L will be used as the EQO for
total ammonia. As ammonia is a component of total nitrogen (TN), the actual effluent
concentration may be limited by the TN EDO rather than the total ammonia EDO. However, as the
TN EQO is based on concern of eutrophication and not a continuous acceptable concentration for
the protection of aquatic life, both EDOs will be presented separately in the ERA.
The WSER requires that un-ionized ammonia concentrations be less than 1.25 mg/L at the discharge
point. For the purposes of this study, the EQO for un-ionized ammonia was chosen based on the
WSER (1.25 mg/L at discharge).
Total Suspended Solids (TSS)
The WSER specifies a limit of 25 mg/L for TSS at the end of the pipe. The CWQG for the protection of
aquatic life in marine water for total suspended solids (TSS) is as follows:
• During periods of clear flow, a maximum increase of 25 mg/L from background levels for any
short-term exposure (e.g., 24-h period). Maximum average increase of 5 mg/L from
background levels for longer term exposures (e.g., inputs lasting between 24 h and 30 d).
• During periods of high flow, a maximum increase of 25 mg/L from background levels at any
time when background levels are between 25 and 250 mg/L. Should not increase more than
10% of background levels when background is ≥ 250 mg/L.
The background concentration of TSS was an average of 32 mg/L. A maximum average increase of
5mg/L from background levels would result in an EQO of 37 mg/L. As this is greater than the WSER
criteria, the WSER criteria of 25 mg/L at discharge will apply as the EDO. The background TSS
measurement is higher than would typically be expected in a marine environment, which may be
due to the near shore location of the samples. However, in a worst case scenario where the
background TSS concentration was 0 mg/L, application of the WSER criteria at the end of pipe would
always be the more stringent criteria provided there is greater than five times dilution.
Total Phosphorus and TKN
There are no CWQGs for the protection of aquatic life for phosphorus or Total Kjeldahl Nitrogen.
However, in both freshwater and marine environments, adverse secondary effects like
eutrophication and oxygen depletion can occur. Guidance frameworks have been established for
freshwater systems and for marine systems to provide an approach for developing site-specific
water quality guidelines. These approaches are based on determining a baseline condition and
evaluating various effects according to indicator variables. The approach is generally very time and
resource intensive, but can be completed on a more limited scale to establish interim guidelines.
The Canadian Guidance Framework for the Management of Nutrients in Nearshore Marine Systems
Scientific Supporting Document (CCME, 2007) provides a framework as well as case studies for
establishing nutrient criteria for nearshore marine systems. This document provides a Trophic Index
for Marine Systems (TRIX), below.
Harbour Engineering Joint Venture Donkin WWTP ERA 13
Table 3.3 Criteria for evaluating trophic status of marine systems (CCME, 2007)
Trophic Status TN
(mg/m3)
TP
(mg/m3) Chlorophyll a (μg/L) Secchi Depth
(m)
Oligotrophic <260 <10 <1 >6
Mesotrophic ≥260-350 ≥10-30 ≥1-3 3-≤6
Eutrophic ≥350-400 ≥30-40 ≥3-5 1.5-≤3
Hypereutrophic >400 >40 >5 <1.5
The background concentrations of TKN and TP were measured as 0.2 mg/L and 0.035 mg/L,
respectively, which corresponds to a eutrophic status based on the phosphorus concentration. The
uppermost limit for this trophic status is a TN concentration of 0.4 mg/L and a TP concentration of
0.04 mg/L.
This document provides another index (NOAA) to determine the degree of eutrophication of the
marine system, below.
Table 3.4 Trophic status classification based on nutrient and chlorophyll (CCME, 2007)
Degree of
Eutrophication
Total Dissolved N
(mg/L)
Total Dissolved P
(mg/L)
Chl a
(μg/L)
Low 0 - ≤0.1 0 - ≤0.01 0 - ≤5
Medium >0.1 - ≤1 >0.01 - ≤0.1 >5 - ≤20
High >1 >0.1 >20 - ≤60
Hypereutrophic - - >60
However, the concentrations in Table 3.4 are based on dissolved nitrogen and phosphorus and the
background concentrations are for TKN and total phosphorus. For nitrogen, with a background
concentration of 0.2 mg/L for TKN, an assumption that the dissolved nitrogen background
concentration is anywhere between 50 and 100% of the TKN background concentration would result
in classification as “medium” based on Table 3.4. For phosphorus, with a background concentration
of 0.035 mg/L, an assumption that the dissolved background concentration is anywhere between 29
and 100% of the total background concentration would result in classification as “medium” based on
Table 3.4.
To maintain the same degree of eutrophication, the total dissolved nitrogen and total dissolved
phosphorus in the receiving water should not exceed the upper limit of the “medium” classification
which is 1 mg/L for Total Dissolved Nitrogen and 0.1 mg/L for Total Dissolved Phosphorus. In
order to determine the upper limit of the “medium” eutrophication range based on total
phosphorus and TN concentrations, an assumption must be made as to the percentage of the
nitrogen and phosphorus that exists in the dissolved phase, both in the receiving water and in the
effluent. As a measure of conservatism, an assumption was made that 100% of the total nitrogen
and phosphorus exist in a dissolved phase. This allows for the upper limits of the “medium”
classification to be used directly as the EQO which results in an EQO of 1 mg/L for TN and 0.1 mg/L
for total phosphorus.
Harbour Engineering Joint Venture Donkin WWTP ERA 14
The Canadian Guidance Framework for the Management of Nutrients in Nearshore Marine Systems
Scientific Supporting Document (CCME, 2007) presents both of the above criteria for assessing
trophic status and does not provide a recommendation for use of one rather than the other.
However, the framework presents a case study to establish nutrient criteria for the Atlantic
Shoreline of Nova Scotia, and the NOAA index is used. Therefore, that index will be used for the
purpose of this study.
pH
The CWQG for the protection for aquatic life for marine waters is 7.0 to 8.7. This pH range will be
applied as the EQO.
Total Residual Chlorine
The WSER requires that TRC concentrations be less than 0.02 mg/L. For the purposes of this study,
the EQO/EDO of 0.02 mg/L for TRC was chosen based on this regulation.
3.3.2 E. coli
Pathogens are not included in the CCME WQGs for the protection of aquatic life. The Health Canada
Guidelines for Canadian Recreational Water Quality specify a maximum E. coli concentration of
200 E. coli/100 mL for freshwater for primary contact recreation and 1000 E. coli/100 mL for
secondary contact recreation. The Health Canada guideline for Canadian Recreational Water Quality
for primary and secondary contact recreation in marine water is based on enterococci rather than E.
coli. However, historical Nova Scotia Environment has set discharge limits for E. coli rather than
enterococci for marine discharges. The background concentration of E. coli was 69 E. coli/100 mL.
An EQO of 200 E. coli/ 100mL will apply for primary contact recreation at the beach in Schooner
Pond Cove. An EQO of 1000 E. coli/ 100mL based on the Canadian Recreational Water Quality
guideline for secondary contact for freshwater will apply elsewhere in the receiving water.
3.3.3 Summary
Table 3.5 below gives a summary of the generic and site-specific EQOs determined for parameters of
concern. The source of the EQO has been included in the table as follows:
• WSER – wastewater systems effluent regulations;
• Background – Site-specific EQO based on background concentration in receiving water;
• CWQG Marine – CCME Canadian Water Quality Guidelines for the Protection of Aquatic Life
Marine;
• USEPA Saltwater – United States Environmental Protection Agency National Recommended
Water Quality Criteria – Aquatic Life Criteria – Saltwater Criterion Continuous Concentration;
• CGF, Marine – Canadian Guidance Framework for the Management of Nutrients in Nearshore
Marine Systems Scientific Supporting Document;
• HC Primary Contact – Health Canada Guidelines for Canadian Recreational Water Quality –
Primary Contact Recreation; and
• HC Secondary Contact – Health Canada Guidelines for Canadian Recreational Water Quality –
Secondary Contact Recreation.
Harbour Engineering Joint Venture Donkin WWTP ERA 15
Table 3.5 EQO Summary
Parameter Generic EQO Background Selected EQO Source
CBOD5(1) (mg/) 25 <5.0 25 WSER
TN (mg/L) 1 0.2 1 CGF, Marine
Total NH3-N (mg/L) 2.7 <0.05 2.7 USEPA Saltwater
Un-ionized NH3-N(1) (mg/L) 1.25 <0.0007 1.25 WSER
pH 7.0 – 8.7 7.71 7.0 – 8.7 CWQG Marine
TP (mg/L) 0.1 0.035 0.1 CGF, Marine
TRC(1) (mg/L) 0.02 NM 0.02 WSER
TSS(1) (mg/L) 25 32 25 WSER
E. coli (MPN/ 100mL) 200 69 200 HC Primary Contact
E. coli (MPN/ 100mL) 1000 69 1000 HC Secondary Contact
Notes:
Bold indicates EQO is a WSER requirement.
(1) EQO applies at the end of pipe.
(2) Although the EQO for ammonia has been calculated to be 2.7 mg/L, an EQO of 1 mg/L for total nitrogen would govern.
However, as the EQO for TN is based on eutrophication, EDOs will be developed for all parameters separately.
Harbour Engineering Joint Venture Donkin WWTP ERA 16
CHAPTER 4 MIXING ZONE ANALYSIS
4.1 Methodology
4.1.1 Definition of Mixing Zone
A mixing zone is the portion of the receiving water where effluent dilution occurs. In general, the
receiving water as a whole will not be exposed to the immediate effluent concentration at the end-
of-pipe but to the effluent mixed and diluted with the receiving water. Effluent does not
instantaneously mix with the receiving water at the point of discharge. Depending on conditions
like ambient currents, wind speeds, tidal stage, and wave action, mixing can take place over a large
area – up to the point where there is no measureable difference between the receiving water and
the effluent mixed with receiving water.
The mixing process can be characterized into two distinct phases: near-field and far-field. Near-
field mixing occurs at the outfall and is influenced by the configuration of the outfall (e.g. pipe size,
diffusers, etc.). Far-field mixing is influenced by receiving water characteristics like turbulence, wave
action, and stratification of the water column.
Within the mixing zone, EQOs may be exceeded but acutely toxic conditions are not permitted
unless it is determined that un-ionized ammonia is the cause of toxicity. If the un-ionized ammonia
concentration is the cause of toxicity, there may be an exception (under the WSER) if the
concentration of un-ionized ammonia is less than or equal to 0.016 mg/L, expressed as N, at any
point that is 100 m from the discharge point. Outside of the mixing zone, EQOs must be achieved.
The effluent is also required to be non-chronically toxic outside of the mixing zone. The allocation of
a mixing zone varies from one substance to another – degradable substances are allowed to mix in a
portion of the receiving water whereas toxic, persistent, and bio-accumulative substances (such as
chlorinated dioxins and furans, PCBs, mercury, and toxaphene) are not allowed a mixing zone.
A number of general criteria for allocating a mixing zone are recommended in the Strategy, including the
following:
• The dimensions of a mixing zone should be restricted to avoid adverse effects on the designated
uses of the receiving water system (i.e., the mixing zone should be as small as possible);
• Conditions outside of the mixing zone should be sufficient to support all of the designated uses
of the receiving water system;
Harbour Engineering Joint Venture Donkin WWTP ERA 17
• A zone of passage for mobile aquatic organisms must be maintained;
• Placement of mixing zones must not block migration into tributaries;
• Changes to the nutrient status of the water body as a result of an effluent discharge should be
avoided; eutrophication or toxic blooms of algae are unacceptable impacts;
• Mixing zones for adjacent wastewater discharges should not overlap; and
• Adverse effects on the aesthetic qualities of the receiving water system (e.g. odour, colour,
scum, oil, floating debris) should be avoided (CCME, 1996).
The limits of the mixing zone may be defined for the following three categories of aquatic
environments based on their physical characteristics:
• streams and rivers;
• lakes, reservoirs and enclosed bays; and
• estuarine and marine waters.
Where several limits are in place, the first one to be reached sets the maximum extent of the mixing
zone allowed for the dilution assessment. Nutrients and fecal coliforms are not allocated any
maximum dilution. For fecal coliforms, the location of the water use must be considered and
protected by the limits of the mixing zone.
Based on these general guidelines, mixing zone extents must be defined on a case-by-case basis that
account for local conditions. It may also be based on arbitrary mixing zone limits for open water
discharges, e.g. a 100 m(1) or 250 m(2) radius from the outfall and/or a dilution limit. A Draft for
Discussion document “Mixing Zone Assessment and Report Templates” dated July 7, 2016, prepared
by a committee of representatives of the environment departments in Atlantic Canada, provides
guidance regarding mixing zones for ERAs in the Atlantic Provinces. This document recommends
that for ocean and estuary receiving waters a maximum dilution limit of 1:1000 be applied for far-
field mixing.
Finally, the assessment shall be based on ‘critical conditions’. For example, in the case of a river
discharge (not applicable here), ‘critical conditions’ can be defined as the seven-day average low
river flow for a given return period. The Standard Method provides the following guidance on EDO
development:
“…reasonable and realistic but yet protective scenarios should be used. The objective is to simulate
the critical conditions of the receiving water, where critical conditions are where the risk that the
effluent will have an effect on the receiving environment is the highest – it does not mean using the
highest effluent flow, the lowest river flow, and the highest background concentration
simultaneously.”
1 Environment Canada, 2006 - Atlantic Canada Wastewater Guidelines Manual for Collection, Treatment, and Disposal
2 NB Department of Environment & Local Government, 2012 Memo.
Harbour Engineering Joint Venture Donkin WWTP ERA 18
As the critical low flow condition is used for the receiving water, the WWTP effluent will be
modelled based on an annual average flow, rather than a maximum daily or hourly flow, as applying
a critical high flow condition for the effluent simultaneously with a critical low flow condition in the
receiving water would result in overly conservative EDOs as this scenario doesn’t provide a
reasonable or realistic representation of actual conditions.
4.1.2 Site Summary
The WWTP is assumed to discharge through an outfall pipe perpendicular to the shoreline in shallow
water, extended to a depth estimated at -1.0 m below low tide. The low tide and -1.0 m depth
contours were estimated based on navigation charts. The total average effluent discharge is
modeled as a continuous point source of 466 m3/day.
The major coastal hydrodynamic features of the area are as follows:
• Along-shore currents along the open coastline are in phase with the tide, i.e. the current
speed peaks at high and low tide; and
• At the outfall site, breaking waves and associated longshore currents will contribute to
effluent dispersion during storms. For this assessment, we have assumed calm summer
conditions (i.e. no waves), when effluent dilution would be at a minimum.
4.1.3 Far-Field Modeling Approach and Inputs
The local mixing zone is limited by the water depth at the outfall of approximately -1.0 m Chart
Datum and by the presence of the shoreline. Since the outfall is in very shallow water, the buoyant
plume will always reach the surface upon release from the outfall3. Far-field mixing will then be
determined by ambient currents, which is best simulated with a hydrodynamic and effluent
dispersion model.
We implemented a full hydrodynamic model of the receiving coastal waters using the Danish
Hydraulic Institute’s MIKE21 model. MIKE21 is ideally suited to the study of outfall discharges in
shallow coastal areas where complex tidal and wind-driven currents drive the dispersion process.
The model was developed using navigation charts, tidal elevations, and wind observations for the
area. A similar model had been used by CBCL for CBRM in the past:
• In 2005 for the assessment of the past wastewater contamination problem at Dominion
Beach, which led to the design of the WWTP at Dominion4; and
• In 2014 for ERAs at the Dominion and Battery Point WWTPs.
The hydrodynamic model was calibrated to the following bottom current meter data:
• 1992 current meters (4 locations) located in 10 m-depth for the study by ASA5 on local
oceanography and effluent dispersion; and
• 2006 current meters (2 locations) off the Donkin peninsula for the CBCL study of mine
effluent dispersion.
3 Fisher et al., 1979. Mixing in Inland and Coastal Waters. Academic Press, London.
4 CBCL Limited, 2005. Dominion Beach Sewer Study. Prepared for CBRM.
5 ASA Consulting Limited, 1994. “Industrial Cape Breton Receiving Water Study, Phase II”. Prepared for The Town of Glace
Bay.
Harbour Engineering Joint Venture Donkin WWTP ERA 19
Calibration consisted of adjusting the following parameters:
• Bottom friction; and
• Model spatial resolution in the area of the current meters.
Numerical Model Domain with Locations of Current Meter Observations and Modeled Outfall
Location are shown in Figure 4.1. Inputs and calibrated outputs are shown in Figure 4.2. The
modelled current magnitudes at New Waterford, Glace Bay, and Donkin are in relatively good
agreement with observations, which is satisfactory to assess the overall dilution patterns of effluent
from the outfall. The effect of waves was not included in the model, and therefore the modeled
effluent concentration near the outfall is expected to be conservatively high.
Figure 4.1 Numerical Model Domain with Locations of Current Meter Observations and
Modeled Outfall Location
Harbour Engineering Joint Venture Donkin WWTP ERA 20
Figure 4.2 Time-series of Hydrodynamic Model Inputs and Calibration Outputs
Harbour Engineering Joint Venture Donkin WWTP ERA 21
4.2 Modeled Effluent Dilution
Snapshots of typical modeled effluent dispersion patterns are shown on Figure 4.3. Statistics on
effluent concentrations were performed over the one-month model run, and over a running seven-
day averaging period. Composite images of maximum and average effluent concentrations are
shown on Figure 4.4.
Effluent concentration peaks at any given location are short-lived because the plume is changing
direction every few hours depending on tides and winds. Therefore, a representative dilution
criteria at the mixing zone limit is best calculated using an average value. We propose to use the
one-day average effluent concentration criteria over the one-month modeling simulation that
includes a representative combination of site-specific tides and winds.
The diluted effluent plume often reaches the shoreline 100 m to the West of the outfall as well as
the shoreline farther away to the south and the northwest at low concentrations. Maximum
concentrations 100 m away from the outfall are typically encountered to the South at low tide, and
to the North at high tide. The 100 m distance from the outfall to the shoreline is within the brackets
of mixing zone radiuses defined by various guidelines. We propose that this distance be used as
mixing zone limit.
The maximum daily average effluent concentration 100 m away from the outfall over the simulation
period is 0.165 % (Table 4.1). Therefore we propose that a 606:1 dilution factor be used for
calculating EDOs based on the maximum 1-day average effluent concentration at 100 m from the
discharge.
Table 4.1 Modelled Dilution Values 100 and 200 m away from the Outfall
Distance
away from
the outfall
Hourly maximum
effluent
concentration
Maximum 1-day
average effluent
concentration
Maximum 7-day
average effluent
concentration
1-Month average
effluent
concentration
100 m 1.567 % (64:1
Dilution)
0.165 % (606:1
Dilution)
0.138 % (725:1
Dilution)
0.105 % (952:1
Dilution)
200 m 0.362 % (276:1
Dilution)
0.080 % (1250:1
Dilution)
0.068 % (1471:1
Dilution)
0.035 % (2857:1
Dilution)
Harbour Engineering Joint Venture Donkin WWTP ERA 22
Figure 4.3 Snapshots of Typical Modeled Effluent Dispersion Patterns
Harbour Engineering Joint Venture Donkin WWTP ERA 23
Figure 4.4 Composite Images of Modeled Hourly Maximum (top) and Maximum 7-Day
Average Effluent Concentrations (middle) with Concentration Time-Series
(bottom)
Note: 100-m radius (black) and 200-m radius (grey) circle shown around outfall.
Harbour Engineering Joint Venture Donkin WWTP ERA 24
CHAPTER 5 EFFLUENT DISCHARGE OBJECTIVES
5.1 The Need for EDOs
Effluent Discharge Objectives (EDOs) represent the effluent substance concentrations that will protect
the receiving environment and its designated water uses. They describe the effluent quality necessary
to allow the EQOs to be met at the edge of the mixing zone. The EQOs are established in Chapter 3; see
Table 3.5 for summary of results.
EDOs should be calculated where reasonable potential of exceeding the EQOs at the edge of the mixing
zone has been determined. Typically, substances with reasonable potential of exceeding the EQOs have
been selected according to the simplified approach: If a sample result measured in the effluent exceeds
the EQO, an EDO is determined. As there are a limited number of parameters considered as substances
of potential concern for very small and small facilities, EDOs will be developed for all substances of
potential concern.
5.2 Physical/ Chemical/ Pathogenic EDOs
For this assessment, EDOs were calculated using the dilution values obtained at the average daily
flow of 466 m3/day that was measured during the metering period. This resulted in a dilution of
606:1 at the edge of a 100 m mixing zone. The model shows a dilution of 2000:1 at Schooner Pond
Beach based on the maximum hourly concentration.
Parameters for which there is a WSER criteria were not allowed any dilution and therefore the EDO
equals the WSER Criteria. The Standard Method does not allocate any maximum dilution for
nutrients and fecal coliforms. For nutrients, it recommends a case-by-case analysis. For fecal
coliforms, the location of the water use must be protected by the limits of the mixing zone.
The dilution values were used to obtain an EDO by back-calculating from the EQOs. When the
background concentration of a substance was less than the detection limit, the background
concentration was not included in the calculation of the EDO.
Harbour Engineering Joint Venture Donkin WWTP ERA 25
5.3 Effluent Discharge Objectives
Substances of concern for which an EDO was developed are listed in Table 5.1 below with the
associated EQO, maximum measured wastewater concentration, and the associated EDO.
Table 5.1 Effluent Discharge Objectives at Proposed Design Conditions
Parameter
Maximum
Wastewater
Concentration
Background Selected
EQO Source Dilution
Factor EDO
CBOD (mg/L) 1400 <5.0 25 WSER - 25
TN (mg/L) 9.7 0.2 1 CGF, Marine 606 488
Total NH3-N
(mg/L) 8.4 <0.05 2.7 USEPA Saltwater 606 1636
Unionized NH3
(mg/L) 0.014 0 1.25 WSER - 1.25
TP (mg/L) 1.5 0.03 0.1 CGF, Marine 606 40
TRC (mg/L) NM NM 0.02 WSER - 0.02
TSS (mg/L) 4100 31.5 25 WSER - 25
E. coli (MPN/
100mL) >240,000 69 200 HC Primary Contact 2000 262,069
E. coli (MPN/
100mL) >240,000 69 1000 HC Secondary Contact 606 564,255
Based on the EDOs calculated above, sample results for the following parameters exceeded the EDO
in at least one wastewater sample:
• CBOD5;
• TSS; and
• E. coli.
These parameters will meet the EDOs at the discharge of the new WWTP through treatment.
Harbour Engineering Joint Venture Donkin WWTP ERA 26
CHAPTER 6 COMPLIANCE MONITORING
The Standard Method utilizes the results of the ERA to recommend parameters for compliance
monitoring according to the following protocol:
• The WSER requirements for TSS, CBOD and unionized ammonia must be monitored to
ensure they are continuously being achieved. Minimum monitoring frequencies are
specified in the guidelines based on the size of the facility. Monitoring of these
substances cannot be reduced or eliminated;
• Nutrients, such as phosphorus and ammonia, and pathogens for which an EDO was
developed should be included in the monitoring program with the same sampling
frequency as TSS and CBOD5;
• For additional substances, the guidelines require that all substances with average effluent
values over 80% of the EDO be monitored;
• If monitoring results for the additional substances are consistently below 80% of the EDO,
the monitoring frequency can be reduced;
• If average monitoring results subsequently exceed 80% of the EDO, monitoring frequency
must return to the initial monitoring frequency; and
• If monitoring results are below 80% of the EDO for at least 20 consecutive samples spread
over a period of at least one-year, monitoring for that substance can be eliminated.
Although the Standard Method results in recommending parameters for compliance monitoring, the
provincial regulator ultimately stipulates the compliance monitoring requirements as part of the
Approvals to Operate. In New Brunswick, the New Brunswick Department of Environment and Local
Government has been using the results of the ERA to update the compliance monitoring program
listed in the Approval to operate when the existing Approvals expire. At this time, it is premature to
use the results of this ERA to provide recommendations on parameters to monitor for compliance,
as the purpose of this ERA was to provide design criteria for design of a new WWTP.
Harbour Engineering Joint Venture Donkin WWTP ERA 27
CHAPTER 7 REFERENCES
ASA Consulting Limited (1994). “Industrial Cape Breton Receiving Water Study, Phase II”. Prepared
for The Town of Glace Bay.
BC Ministry of Environment (2006). A Compendium of Working Water Quality Guidelines for
British Columbia. Retrieved from: http://www.env.gov.bc.ca/wat/wq/BCguidelines/working.html
CBCL Limited (2005). Dominion Beach Sewer Study. Prepared for CBRM.
CCME (2008). Technical Supplement 3. Canada-wide Strategy for the Management of Municipal
Wastewater Effluent. Standard Method and Contracting Provisions for the Environmental Risk
Assessment.
CCME (2007). Canadian Guidance Framework for the Management of Nutrients in Nearshore
Marine Systems Scientific Supporting Document.
CCME Canadian Environmental Quality Guidelines Summary Table. Water Quality Guidelines for the
Protection of Aquatic Life.
Environment Canada (2006). Atlantic Canada Wastewater Guidelines Manual for Collection,
Treatment and Disposal
Environment Canada (Environment Canada) (1999). Canadian Environmental Protection Act Priority
Substances List II – Supporting document for Ammonia in the Aquatic Environment. DRAFT –August
31, 1999.
Fisher et al. (1979). Mixing in Inland and Coastal Waters. Academic Press, London.
Fisheries Act. Wastewater Systems Effluent Regulations. SOR/2012-139.
Health Canada (2012). Guidelines for Canadian Recreational Water Quality. Retrieved from:
http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/guide_water-2012-guide_eau/index-eng.php
Mixing Zone Assessment and Report Template Draft only – For discussion (July 7, 2016)
NB Department of Environment & Local Government, (2012). Memo.
Harbour Engineering Joint Venture Donkin WWTP ERA 28
Thomann, Robert V. and Mueller, John A (1987). Principles of Surface Water Quality Modeling and
Control.
UMA (1994). Industrial Cape Breton Wastewater Characterization Program, Phase II.
USEPA. National Recommended Water Quality Criteria for Saltwater. Retrieved from:
http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm
Prepared by: Reviewed by:
Holly Sampson, M.A.Sc., P.Eng. Karen March, M.Sc.
Intermediate Chemical Engineer Environmental Scientist
Harbour Engineering Joint Venture Appendices
APPENDIX A
Laboratory Certificates
HEJV Donkin Wastewater System Pre-Design Summary Report Appendices
APPENDIX D
Donkin Wastewater Treatment Facility Site
Desktop Geotechnical Review
October 22, 2018 SYD-00245234-A0/60.2
Mr. Terry Boutilier
Dillon Consulting Limited
275 Charlotte Street
Sydney, NS B1P 1C6
Re: Wastewater Treatment Plant Geotechnical Desktop Study
Donkin Site
Dear Mr. Boutilier:
It is the pleasure of EXP Services Inc. (EXP) to provide Dillon Consulting Limited (Dillon) with this letter
report summarizing the preliminary review completed by EXP on the potential site for the
construction of a wastewater treatment facility in Donkin, Nova Scotia.
Background
A geotechnical desktop study is an essential tool used by engineers to identify and gather as much
information as possible pertaining to the probable ground conditions at a proposed construction site
without commissioning an intrusive ground investigation. The information obtained from the desktop
study will identify potential problems, hazards and/or constraints associated with the probable ground
conditions in the proposed area of construction, as well as provide geotechnical recommendations for
new construction activities. When a walkover survey is completed in conjunction with the desktop
study it will allow engineers to refine and enhance their understanding of each of the sites in relation
to the topography, earth exposures, drainage conditions, etc. When completed together (the desktop
study and the walkover survey), the findings will provide invaluable information in the early stages of
the design at a negligible cost. It is the intent of the desktop study and walkover survey not only to look
at the site, but also at its surroundings. Noted below are the key findings to be reported in any desktop
study and walkover assessment:
• site topography;
• geology (surficial ground cover, probable overburden soil and bedrock type);
• geotechnical problems and parameters;
• previous land use (aerial photographs);
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• underground/surface mining activities; and
• proposed supplemental ground investigation methods (test pits and/or boreholes).
Subject Site Description and Topography
The proposed site for the new wastewater treatment plant (WWTP) is located near Bordens Head, off
of Bastable Street in Donkin, Nova Scotia, and is identified by two Property Identification Numbers (PID)
Numbers, 15277353 and 15495021. The subject property is relatively level, but rises slightly from the
southwest toward the northeast. The property then drops off rapidly along the Atlantic coastline (cliff
face). The property is bound by the Atlantic coastline along the northern and western perimeters of the
site and forested/marsh areas along the eastern and southern perimeters of the site. Figure 1 depicted
below outlines the proposed location of the site.
Figure 1: Proposed location of the new WWTP in Donkin.
Engineered Wetland
Stabilization Ponds
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Published Geological Mapping (Surficial and Bedrock)
Review of the surficial geological mapping of the study area indicated that the subsurface geology
consists of a Stony Till Plain. This type of till is generally comprised of a stony, sandy matrix material
with varying amounts of cobbles and boulders and can vary in thickness from 2 to 20 metres thick.
Typically, these materials were released from the base of ice sheets during the melting process of the
ice sheet.
A review of the existing bedrock mapping for the area indicates that the site is underlain by materials
from the late carboniferous period, which are identified in this area as material from the Sydney Mines
Formations of the Morien Group. These formations are comprised of fluvial and lacustrine mudstone,
shale, siltstone, limestone and coal.
A review of historical mapping and online reference documents indicated that mining activities have
been carried out extensively in an area west and southwest of the proposed construction site (but not
directly under the site). The workings were the standard room and pillar coal extraction process. It
should be noted that pillars may have been mined at some point during mining activities. Mapping
indicates that the site is just north of the Backpit Seam and south of the Bouthillier Seam outcroppings.
Existing Ground Conditions
At the time of the investigation, the site was primarily covered in either densely wooded areas, peat
bogs and/or marshy areas. All-terrain vehicle (ATV) trails were observed crisscrossing over the site
(through wooded, peat bog and marshy areas), exposing the underlying glacial till and/or marshy soils.
The overburden soil (glacial till) exposure was observed along the cliffside. The thickness of the
overburden appears to be in the range of 0.3 to 0.5 metres thick (thicker accumulations are expected
deeper inland). The glacial till was visually described as being a silty SAND with gravel and varying
amounts of cobbles. Limestone cobbles were observed scattered across the site. The till mixture is in a
compact state of relative density. The till should provide satisfactory bearing stratum for the support
of shallow foundations with bearing capacities between 150 and 200 kPa. The underlying bedrock
would provide a higher capacity for allowable bearing.
Visual review of rutting of the peat bog and marshy areas revealed that these materials varied in
thickness of 0.2 to 0.5 metres in depth. Thicker accumulations of these material are possible across the
site. The peat bog and mossy area overburden materials are not suitable for construction and should
be completely removed from the footprint of the facility.
The bedrock underlying the till was also observed along the cliffside. The exposed bedrock consisted of
alternating layers of shale, mudstone, sandstone and/or siltstone. The formations are consistent with
the material identified in the regional mapping. The exposed bedrock along the Atlantic coastline is
showing evidence of erosion.
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Geotechnical Problems and Parameters
Summarized below are the key geotechnical problems of the site.
• There is evidence of the erodibility of subsurface soils and bedrock exposure along the Atlantic
coastline. A Coastal Protection Plan will be required for this site.
• The area adjacent to the southwest of the site was undermined due to historical coal mining
activities and there is a potential for undocumented bootleg pits/mines in the area.
• There is the potential for a layer of limestone to be present underlying the surficial ground and
alternating layers of bedrock below the site. Limestone is water soluble and has the potential
to develop karsts voids (sinkholes).
• It is anticipated that the overburden soil will be in a very moist to wet condition near the
surface, in particular near the marshy/boggy areas. This will create some problems during site
preparation and construction. A Surficial and Groundwater Control Plan should be developed
for the site.
• The presence of uncontrolled fills is suspected on the southern corner of the site due to
historical activities on the site for the installation of a sanitary sewer discharge line into the
harbour.
Previous Land Use
Aerial photographs from 1931 to 2018 have been reviewed and are summarized below.
• An aerial photograph taken in 1931 depicts the site void of any structures. It was primarily
covered in a marshy/swampy area with low lying vegetation and trees. A footpath traverses
the site from along the southern border of the site. Mining activities and infrastructure are
visible southwest of the site in the center of the Town. Residential dwellings were observed to
the west and south of the site.
• An aerial photograph taken in 1947 depicts little to no discernable change to the site since the
1931 photograph was taken. The infrastructure for the mine observed in the 1931 photograph
appears to have been removed/dismantled.
• An aerial photograph taken in 1953 depicts little to no discernable change to the site since the
1947 photographs was taken. Some larger trees, along the eastern edge of the site, have been
cleared.
• An aerial photograph taken in 1963 depicts little to no discernable change to the site since the
1953 photograph was taken. Vegetation and tree coverage bordering the subject site has
increased in density.
• An aerial photograph taken in 1973 depicts little to no change to the site since the 1963
photograph.
• An aerial photograph taken in 1977 depicts little change to the site since the 1973 photograph
was taken. The footpath bordering the southern perimeter of the site (identified as early as
1931) was expanded in its width and is connected to the north end of Bastable Street. An
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additional roadway/cut line was installed off Bastable Street (at the intersection with the
footpath) and was extended westerly through Briffett Street and connected with North Street.
• An aerial photograph taken in 1987 depicts little to no discernable change to the site since the
1977 photograph was taken. The roadway/cutline, off of Bastable Street and the former
footpath, has been overgrown with vegetation.
• Aerial photographs taken between 1993 and 2018 shows an increase in density of tree
coverage on the site.
Proposed Supplemental Ground Investigation Methods
It is also recommended that a preliminary geotechnical investigation (land based drilling) be completed
at the site to verify the presence or absence of authorized and/or bootleg mining activities undertaken
in the area, as well as the potential of future subsidence that could impact structures constructed on
the site.
Ultimately, the goal of the supplemental geotechnical ground investigation is to collect pertinent
information pertaining to the subsurface conditions within the footprint of the proposed new facility.
This information will then be used to develop geotechnical recommendations for use in the design and
construction of the new facility.
Borehole locations should be selected based upon the location of buried infrastructure (sewer, water,
electrical and fiber optic lines) and to provide adequate coverage of the site. It is proposed that
representative soil samples be collected continually throughout the overburden material of each of the
four boreholes advanced at the site. Additionally, it is recommended that during the investigation
samples of the bedrock should be collected continuously to a depth of at least 30 metres or more, in
two of the four boreholes. The intent of the bedrock coring is to:
• verify the presence or absence of underground mine workings (both authorized commercial
activities and/or bootleg pits).
• increase the odds of advancing the borehole through the roof of any mine working (to
determine the potential void space) and not into a supporting pillar (if applicable).
• accurately characterize the bedrock for design of either driven or drilled piles, if needed.
It is recommended that the remaining two boreholes be terminated either at 12 metres depth below
ground surface or once refusal on assumed bedrock is encountered (whichever comes first). It should
be noted that if pillar extraction took place, fractures will likely extend 20 metres above mine workings.
If this is the case, drill return water may be lost and rock wedges may be encountered. This will inhibit
coring and an alternative method of drilling through fractured rock may have to be pursed.
A Geotechnical Engineer should oversee the advancement of each of the boreholes. A CME 55 track
mounted geotechnical drill rig (or equivalent), equipped with bedrock coring equipment and a two-
man crew (driller and helper), should be used to advance each of the boreholes. Representative soil
samples should be attained from a 50 mm diameter standard split spoon sampler during Standard
Penetrating Tests (SPT) conducted ahead of the casing and/or auger equipment. A preliminary
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assessment of each recovered sample should be completed for particle size, density, moisture content
and color. The SPT should continue until refusal or contact with assumed bedrock. Bedrock should be
confirmed through coring of the material using coring equipment and drill casing. Each core sample
should be removed from the core barrel and placed into core boxes for identification.
Upon completion of the intrusive portion of the program, all boreholes are to be plugged (at various
depths within the borehole) using a bentonite plug and backfilled to grade using silica sand. It should
be noted that continuous grouting (with neat cement and/or bentonite) may be required to backfill the
boreholes to grade. The continuous grouting will protect water supplies from contamination sources;
it can prevent the movement of water between aquifers; and prevent and stabilize the water soluble
bedrock that may be present on the site. Following the installation and backfilling activities, the location
and elevations are to be determined using Real Time Kinematic (RTK) survey equipment in the AST 77
coordinate system.
This letter report is prepared for the Donkin site. Should you have any questions or concerns, please
contact John Buffett or Gary Landry at 902.562.2394.
Sincerely, Sincerely,
John Buffett, P.Eng., B.Sc., RSO Gary Landry, P.Eng., B.Sc.
Project Engineer Project Manager
EXP Services Inc.
HEJV Donkin Wastewater System Pre-Design Summary Report Appendices
APPENDIX E
Donkin Wastewater System Archaeological
Resources Impact Assessment