Construction underway on Durham Region’s $164 million wastewater system upgrade
By Marek Krynski, P.Eng., and George Powell, P.Eng.
Artist’s renditions of digesters (top) and headworks building.
With a population now
approaching 600,000 and
projected to reach over
900,000 in the next 15
years, Ontario’s Durham Region is one
of Canada’s fastest growing municipalities.
The single most significant
growth pressure the Region faces is a
dramatic increase in residential development,
which in turn, stresses its 11
wastewater treatment facilities.
One of the region’s larger facilities,
the Harmony Creek Water Pollution
Control Plant (WPCP), which services
the communities of Oshawa and
Courtice, is nearing its rated capacity
of 68,200 m3/d (15 MIGD). Half of the
secondary treatment process comprises
a trickling filtration facility, commissioned
in 1962, which is now
reaching the end of its useful life.
Significant upgrading and/or replacement
is needed for the WPCP to meet
its present effluent requirements. It is
also important to note that the present
Water Pollution Control Plant site is
insufficient to accommodate the
planned growth in the area.
Therefore, in March 1999, the
Regional Municipality of Durham
completed a class environmental
assessment (EA) for additional water
pollution capacity for the Whitby,
Oshawa, and Clarington (Courtice)
areas. The report recommended establishing,
in the municipality of
Clarington, a new water pollution control
plant (WPCP) with an ultimate
average day design flow capacity of
272,760 m3/d (60 MIGD). The plan is
for the ultimate decommissioning
(over time) of the Harmony Creek
WPCP, and conveyance of the tributary
flow to the new Courtice WPCP.
Initially, only Harmony Creek WPCP
No. 1, the trickling filter facility, will
be decommissioned. All average day
flows in excess of 34,100 m3/d (7.5
MIGD), the rated capacity of Harmony
Creek WPCP No.2, will be conveyed
to the new Courtice WPCP.
The Courtice WPCP is being constructed
in phases with the first phase,
presently under construction, having a
capacity of 68,200 m3/day (15 MIGD)
and scheduled for completion in the
fall 2007.
The selected site for the WPCP is in
southeast Durham and has an area of
65.5 hectares (ha). It abuts Lake
Ontario, immediately east of Courtice
Road, south of the Canadian National
Railway (CNR) main line, and west of
the Darlington nuclear generating station.
The Project
The main components of the
Courtice Water Pollution Control Plant
project are:
The Harmony Creek Pumping
Station.
Conveyance of flows to the Courtice
WPCP.
The Courtice WPCP.
The outfall into Lake Ontario.
Harmony Creek Pumping Station
The Harmony Creek Pumping
Station will be located on the
north–west corner of the existing
Harmony Creek WPCP site, abutting
Colonel Sam Drive. The station will
have an initial Phase 1 peak wet weather
capacity of 171,072 m3/day (37.6
MIGD), a Phase 2 capacity of 241,920
m3/day (53 MIGD), and an ultimate
station capacity of 331,517 m3/day (73
MIGD).
The station will house the following
equipment:
Two mechanically cleaned bar
screens with 50 mm spacing.
Six submersible pumping units with
space for an additional 4 units (initially).
Two discharge headers located in the
basement of the pumping station
designed for ultimate flow conditions.
A 2000 kW prime duty stand-by
diesel generator.
Artist’s renditions of liquid train secondary gallery (top) and liquid train.
Conveyance
Conveyance from the Harmony
Creek Pumping Station to the Courtice
WPCP will be along Colonel Sam
Drive to the Darlington Provincial
Park, and more or less paralleling the
alignment of the CN main line to the
Courtice WPCP, a distance of 6.5 km.
Initially, one 1050 mm diameter forcemain
will be constructed. There is
space in the conveyance easement for a
second forcemain and a 300 mm
Regional watermain, which will be
constructed with the forcemain to
service the WPCP site and future
growth in the Courtice area.
The forcemain alignment crosses
Tooley, Robinson, and Harmony Creek
as well as marshlands to the west at
Second Marsh and McLaughlin Bay.
As a result, in these environmentally
sensitive areas, special mitigation
measures will be implemented in constructing
the forcemains. The main
agencies involved in gaining approval
for the alignment included the Central
Lake Ontario Conservation Authority,
the Ontario Ministry of Natural
Resources, the Ontario Ministry of the
Environment, the Federal Department
of Fisheries and Oceans, as well as the
municipalities of Oshawa and
Clarington, and the Friends of the
Second Marsh.
Courtice WPCP
Numerous treatment processes
were evaluated during the Class
Environmental Assessment process,
including the conventional activated
sludge process, sequencing batch reactor
(SBR) process, trickling filter
process, rotating biological contactor
process, and constructed wetland systems.
Based on the assessment, it was
concluded that the Courtice WPCP
will generally consist of a nitrifying
activated sludge process with chlorination/
dechlorination for disinfection,
and conventional anaerobic digestion
for solids treatment and on-site
biosolids storage. The plant site development
allows for the possibility of
future biological nutrient removal and
UV disinfection to be added, and
solids handling processes (including
biosolids dewatering and incineration
or composting) could be provided
.
Initially, the Courtice WPCP will be
designed for 68,200 m3/day (15
MIGD) and will have a peak wet
weather flow of 2.65 times the design
flow, or 180,730 m3/day (40 MIGD).
The plant will be designed in stages to
provide “just in time delivery” of
capacity. Battery sizes are 34,200
m3/day (7.5 MIGD). For the ultimate
plant capacity of 272,800 m3/day (60
MIGD), a total of eight batteries are
proposed and can be readily accommodated
on site.
Effluent compliance requirements,
as stipulated by the Ministry of
Environment, are found in Table 1.
The new Courtice Water Pollution
Control Plant (WPCP) will consist of
the following unit processes:
Preliminary Treatment: Headworks
with screening and aerated grit
removal.
Primary Treatment: Rectangular
chain and flight primary clarifiers.
Secondary Treatment: Nitrifying
activated sludge with anoxic selectors,
energy efficient fine bubble aeration,
and phosphorus removal by application
of metallic salts followed by
“Gould type” rectangular chain and
flight secondary clarifiers.
Disinfection: Final effluent disinfection
via chlorination/dechlorination
using liquid chemical addition.
Solids Treatment: Conventional
anaerobic digestion of raw primary
solids and waste solids from secondary
treatment, and on-site biosolids and
raw sludge storage tanks.
Outfall
As part of the Courtice WPCP project,
a 1676 mm diameter outfall will
be provided, sized to meet the Phase 2
peak flow requirements.
The outfall consists of an outfall
pipe with a staged diffuser section. To
handle the peak capacity, forty-five
diffusers spaced over a distance of 150
m are provided to diffuse effluent in
Lake Ontario, approximately 1 km off
shore in 9 to 11 m of water.
As an important part of the
Courtice project, a study area for the
new outfall was defined. This area was
identified based on pollutant plume
modelling completed during the Class
EA and on geotechnical and aquatic
information. The plume modelling
indicated that the outfall diffuser at the
Darlington Nuclear Generating Station
(DNGS) has significant impact upon
the nearshore currents, and therefore,
on the Courtice effluent plume offshore
of South Courtice.
The large heated water discharge
from the DNGS outfall provides a high
initial dilution and pushes the effluent
plume offshore away from the beach at
Darlington Provincial Park as well, as
DNGS’s water intake. It was therefore
concluded that the best location for the
effluent outfall would be as close to the
DNGS heated water discharge as practically
possible.
The modelling also indicated that to
meet MOE effluent dilution requirements,
the outfall diffusers must be located within a water depth at least of
six metres. The proposed outfall diffusers
will be at water depths of 9 to 11
m, providing better than over 46 to 1
dilution at ultimate peak flow capacity.
Within the study area, three possible
alignments for the outfall were
identified that allowed the outfall to be
close to DNGS outfall, and meet effluent
dilution requirements. These alignments
were along the westerly edge of
the study area, the easterly edge, and a
location in the middle.
To identify the preferred location,
bathymetry, habitat, and geotechnical
investigations of the lake bottom were
conducted on the three potential pipe
alignments. The aquatic study included
a video of the bottom describing the
surface features and fish and aquatic
growth observed, along with bathymetry
and soil sampling and analysis. Soil
investigation to shale bedrock was carried
out in the lake to determine the
sub surface soil conditions. These
investigations concluded that the most
westerly alignment for the outfall is
preferred, due to the following:
Clays are present and are highly
plastic, potentially reducing siltation
concerns. Blasting is not thought to be
necessary.
It avoids the ridge of dense sandy
silt till towards the east.
There is an absence of useable fish
habitat.
The distance to satisfactory depth
of water for effective diffusion is
shorter than the other locations.
The methods of construction of the
outfall at the preferred alignment were
documented in the Environmental
Study Report (ESR). These methods
included either an open trench marine
excavation, totally or partially buried,
or as a tunnel. After careful review, the
construction method chosen was open
trench marine construction.
Project Team
The Region of Durham is supported
by a team responsible for various parts of
the project, as follows: Region of Durham
Works Department; Stantec Consultants –
Program Management; Team Courtice –
CH2M HILL Canada, MacViro
Consultants; Simcoe Engineering Group –
WPCP and prime technical consultant;
Earth Tech – Harmony Creek Pumping
Station; Totten, Sims, Hubicki (TSH) –
Conveyance; R.V. Anderson Associates
(RVA) – Outfall.
There is also support from specialists,
including Geo-Canada, Golder
Associates (geotechnical), ASI Group
(Aquatic), C.B. Fairn & Associates
(Marine Construction Specialist),
Warmé Engineering and Biological
Services (Biology), and Archaeological
Services (Archaeology).
Constructors
In July 2005, the Region of Durham
awarded the Courtice WPCP to
Kenaidan Contracting Ltd., in the
amount of $88,870,000, and the
Outfall into Lake Ontario to McNally
International Inc., in the amount of
$8,513,000. The Conveyance contract
from the Harmony Creek WPCP to the
new Courtice WPCP is scheduled for
tendering in the late fall of 2005 and
the Harmony Creek Pumping Station
is scheduled for tendering in early
2006. The current estimate for the
overall program is $163,950,000.
Marek Krynski, P.Eng., is with the
Regional Municipality of Durham.
George Powell, P.Eng., is with CH2M
HILL.
Contact e-mail: lstory@ch2m.com.
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