October 26, 1998
To:Works and Utilities Committee
From:Executive Director, Technical Services
Subject:Eastern Beaches Water Quality - Effectiveness of the Kenilworth Avenue and Maclean Avenue Detention Tanks
In response to the postings that occurred at the Eastern Beaches during the 1998 swimming season, the Commissioner of
Works and Emergency Services was requested to report to your Committee on the effectiveness of the Kenilworth Avenue
and Maclean Avenue detention tanks in improving the water quality at the Eastern Beaches and the reason for the 1998
Funding Sources, Financial Implications and Impact Statement:
It is recommended that this report be received for information.
The Works and Utilities Committee at its meeting of July 15, 1998, recommended the adoption of the report dated June
26, 1998 from the General Manager of Water and Wastewater Services, Works and Emergency Services, regarding
Geotechnical Consulting Services for the Western Beaches Storage Tunnel and, inter alia, requested the Commissioner of
Works and Emergency Services to immediately alert the media to the success of the Western Beaches Storage Tunnel
project and to provide an update on the pollution counts at all the beaches, including Woodbine Beach (Clause 6 of Works
and Utilities Committee Report No. 7, which was adopted by City Council on July 29, 30 and 31, 1998 without
amendment). For your information, this report contains the trend analysis on the Eastern Beaches and the impact of the
detention tanks since commencement of their operation.
Comments and/or Discussion and/or Justification:
In the 1980's, the frequency of beach postings resulted in extensive environmental monitoring and analysis of conditions
at the Eastern Beaches to determine the main factors responsible for the impaired water quality. From these studies, it was
determined that the primary cause of these degraded conditions was the rainfall related discharges from both the combined
sewer overflow (CSO) and storm sewer outfalls which outlet to the nearshore beach area of the Eastern Beaches. It was
concluded that the most effective manner in which to deal with these discharges was to construct two underground tanks
at the Eastern Beaches to intercept and detain the sewer flows.
The first of the two detention tanks was constructed in the park at the foot of Kenilworth Avenue at a gross cost of $4.1
million. The Kenilworth Avenue detention tank went into operation in July 1990 and it has a capacity of 2,200 m3. It
intercepts the flows from one CSO and four storm sewers located between Woodbine Avenue and Lee Avenue. This
detention tank was designed to capture and detain the storm runoff from the majority of rainfall events during the
swimming season. On average, the capacity of this detention tank will be exceeded once per swimming season resulting in
the discharge of the excess flows to the nearshore beach area via the overflow outfall. During the remaining runoff events,
the captured flows are detained until there is adequate capacity in the Lakefront Interceptor, at which time they are
released at a controlled rate to the interceptor for conveyance to the Main Treatment Plant.
The second facility was constructed on the beach opposite Maclean Avenue at a gross cost of $9.4 million. The Maclean
Avenue detention tank went into operation prior to the start of the 1995 swimming season. It has a total capacity of 8,000
m3 which is divided between two compartments of 4,000 m3. The detention tank's total capacity of 8,000 m3 enables it to
detain the flows from all but two or three major rainfall events which may occur on average during the swimming season.
The Maclean Avenue detention tank intercepts the flows from the Glen Manor Road and Balsam Avenue storm sewers as
well as the Maclean Avenue CSO. The flows from the two storm sewers are detained in the detention tank's south
compartment for a period of 10 hours to enable the sedimentation process to proceed. At the end of this prescribed
detention period, the decanted flows are pumped 400 m offshore where they do not impact the nearshore beach area. Once
the dewatering of the storm compartment is completed, the solids that have settled on the tank floor after sedimentation
are pumped to the Lakefront Interceptor for conveyance to the Main Treatment Plant.
The flows from the Maclean Avenue CSO are intercepted by the detention tank's north compartment and detained until
there is adequate capacity in the Lakefront Interceptor to enable these flows to be conveyed to the treatment plant.
The overall impact of the Kenilworth Avenue and Maclean Avenue detention tanks is that the stormwater flows and
CSO's from 289 hectares, or 89% of the Eastern Beaches drainage area which were discharged untreated directly to the
nearshore beach area, are now intercepted by the detention tanks. These captured flows are either diverted to the Main
Treatment Plant or detained and subjected to treatment via the sedimentation process enabling the "cleaner" flows to be
There are four storm sewer outfalls at the extreme east end of the Eastern Beaches that continue to discharge directly to
the nearshore. However, this area is not actively utilized for swimming.
Detention Tank Effectiveness:
The beaches are posted by the Medical Officer of Health when the bacteriological concentration at the nearshore beach
area exceeds the provincial guideline. Currently, the guideline is based on the geometric mean of the levels of E. coli
bacteria within a particular beach area. If the geometric mean exceeds the provincial guideline of 100 E. coli per 100 ml,
the beach is considered unsuitable for swimming or bathing.
The Eastern Beaches are comprised of four beaches as shown in Figure 1. Throughout the summer months, water samples
are collected from five locations at each of these four beaches and analyzed to determine the E. coli levels. It is these
analytical results which the Medical Officer of Health uses in calculating the 2-day geometric mean to determine whether
or not to post the beach.
Figure 2 illustrates, on an annual basis since 1986, the percentage of the total days during the swimming season (June to
August inclusive), that the provincial guideline in effect at that time was exceeded at each of the four beaches. An
examination of this figure shows that in the years following completion of the detention tanks, there is a pronounced
decrease in the percentage of days that the guideline was exceeded.
For the years 1986 to 1988 inclusive, when neither of the detention tanks were in operation, the provincial guideline was
exceeded over the entire Eastern Beaches an average of 36% of the days during the swimming season. As indicated above,
the Kenilworth Avenue detention tank went into operation in July 1990. The location of the Kenilworth Avenue detention
tank, and the sewers it intercepts, result in it having the most significant impact on Woodbine Beach and Beaches Park.
From 1990 to 1994 inclusive, the provincial guideline was exceeded at Woodbine Beach and Beaches Park for an average
of only 7.6% of the days during the swimming season, while at Kew Beach and Balmy Beach, the guideline was exceeded
on an average of 21.9 % of the days.
The completion of the Maclean Avenue detention tank prior to the start of the 1995 season, provided a direct benefit to
both Kew Beach and Balmy Beach. From 1995 to 1998, with both the detention tanks in operation, the average number of
days during the swimming season that the guideline was exceeded was as follows:
Percentage of Days Provincial
Woodbine 3.0 %
Beaches Park 4.1 %
Kew 3.8 %
These average values for the period from 1995 to 1998 inclusive, illustrate that since the Kenilworth Avenue and Maclean
Avenue detention tanks were constructed, there has been a definite reduction in the occurrence of water quality conditions
that exceed the provincial guideline. It is evident from Figure 2, that on an annual basis there has been a general decline in
the frequency the provincial guideline has been exceeded at the Eastern Beaches as each of the detention tanks
The Kenilworth Avenue and Maclean Avenue detention tanks not only improve the water quality of the Eastern Beaches
by reducing the bacteriological loadings, they also reduce the overall loading to the lake of other contaminants associated
with urban runoff. By intercepting and detaining these flows and either directing them to the Main Treatment Plant or
subjecting them to the sedimentation process prior to their release, the contaminant loads discharged to the lake are
Works and Emergency Services has monitored the quality and quantity of the inflows and discharges from the Maclean
Avenue detention tank to determine the suspended solids, heavy metals and nutrient concentrations. From this monitoring
data, it is possible to determine the average contaminant concentration of the stormwater inflows to the detention tank and
the average contaminant concentration of the flows discharged to the lake following the 10-hour detention period. An
approximate indication of the load reduction can be obtained by applying these average concentrations to the annual flow
volume intercepted by the detention tanks and the volume discharged to the lake. The following illustrates the 1997 loads
for some of the contaminants from only the stormwater flows intercepted by the detention tank and the corresponding
loads of the stormwater flow discharged following the detention period:
1997 Maclean Avenue Detention Tank
ParameterAnnual Loading (kg)
Flow to PlantDischarged to LakeTotal
Biochemical Oxygen Demand1,7506502,400
ND = Below Detection Limit
The total loads listed above would resemble the condition that existed prior to the detention tanks when these contaminant
loads would have been discharged directly to the lake. As illustrated above, with the Maclean Avenue detention tank in
operation, the contaminant loading to the lake solely from stormwater runoff has been substantially reduced.
By understanding that both the stormwater and CSO flows intercepted by the Kenilworth Avenue detention tank and only
CSO flows from the Maclean Avenue detention tank are sent to the Main Treatment Plant and not discharged to the lake,
the overall contaminant load reduction from both detention tanks is actually greater than the contaminant load reduction
for stormwater only as shown above for the Maclean Avenue detention tank. In 1997, between the CSO flow from the
Maclean Avenue detention tank and the storm and CSO flows from the Kenilworth Avenue detention tank, a further 7,900
kg of suspended solids was diverted at a controlled rate to the Main Treatment Plant. Therefore, based on data provided by
limited sampling, if the detention tanks did not exist, a total of 45,100 kg of suspended solids from storm runoff and CSO
would have been discharged to the lake at the Eastern Beaches in 1997. However, because of the detention tanks, the
actual loading was reduced to 2,800 kg.
A similar load reduction is evident for other contaminants associated with urban runoff. These contaminant load
reductions reflect the additional benefit offered by both the Kenilworth Avenue and Maclean Avenue detention tanks
which not only maintain the bacteria concentrations at levels that enable swimming to occur at the Eastern Beaches, but
by also improving the overall water quality at the Eastern Beaches.
1998 Eastern Beaches Posting:
The 1998 postings by the Medical Officer of Health at the Eastern Beaches occurred following the rainfalls of July 7 and
July 8. The subsequent sampling determined that there were elevated E. coli levels at all four of the Eastern Beaches. The
resulting 2-day geometric means for Wednesday, July 8 and Thursday, July 9 were greater than the provincial guideline,
requiring the Medical Officer of Health to post the beaches.
Both the detention tanks functioned as designed during this period. They were able to accommodate the resultant storm
runoff from these rainfall events without exceeding their detention capacities and consequently, there was not a nearshore
overflow. However, during this period, the wind was blowing from east to west across the Eastern Beaches. This easterly
wind, and the associated lake current it generated, had the effect of transporting, to the monitored beaches, the discharges
from those four storm sewer outfalls which continue to discharge to the nearshore area. In addition, it is suspected that
these winds created turbulent conditions within the nearshore area which resulted in the resuspension of sediment which
may also contribute to an increase in the E. coli levels.
The beach sampling and analysis that occurred during this period detected elevated E. coli levels which necessitated the
need to post the beaches. The change in wind and current direction on July 9 resulted in improved water quality, as was
reflected in the lower sample results for this day. However, the 2-day mean on July 9 still exceeded the provincial
guideline due to the elevated readings from the previous day, which are used in addition to the sample results from July 9,
in calculating the 2-day geometric mean.
The actual beach posting remained in effect for six days until it was removed on Wednesday, July 15. This extended
posting can be attributed to the fact that no sampling is conducted on Fridays or on the weekends, and that the Medical
Officer of Health will only remove the posting following two consecutive days when the 2-day geometric mean is less
than 100 E. coli/100 ml. Therefore, the Medical Officer of Health had to wait for the sample results of Monday, July 13
and Tuesday, July 14, both of which were significantly less than the provincial guideline, before the posting could be
The 1998 postings of the Eastern Beaches were not the result of any operational deficiencies with the Kenilworth Avenue
or Maclean Avenue detention tanks. The wind and current conditions prevalent during this period were the factors that
contributed to the poor water quality. They resulted in the resuspension of the lake bed sediments and enabled the
contaminated sewer discharges from those sewer outfalls within the Eastern Beaches area, and possibly those from beyond
the east limit of the Eastern Beaches, to be transported to the monitored beaches. Both events would have the effect of
impairing the water quality at the Eastern Beaches.
Figures 3 to 6 show the 2-day E. coli geometric means for 1998 at each of the four Eastern Beaches and the rainfall that
occurred during the swimming season. It can be seen that throughout the 1998 season, the detention tanks were effective
in capturing the storm flows from these rainfalls, thereby preventing them from adversely impacting the water quality of
the Eastern Beaches.
By examining the conditions that existed prior to the construction of the two detention tanks, it can be seen that these
facilities have had a profound impact on reducing the frequency the provincial guideline was exceeded at the Eastern
Beaches, and thereby the need for the Medical Officer of Health to post these beaches. Although other environmental
factors, beyond the capability of the detention tanks to influence, can result in short-term impaired water quality, the
detention tanks have provided a significant benefit to the Eastern Beaches. In comparison, from 1995 to 1998, the Western
Beaches, which are still affected by sewer discharges, have been posted for more than 65% of the time during the
Contact Name and Telephone Number:
Alex Marich, Environmental Engineer
Environmental Services Section, Technical Services Division
Works and Emergency Services
Toronto Community Council Area
Phone: (416) 392-7705
Fax: (416) 392-1456
Tom Denes, P.Eng.Barry H. Gutteridge
Executive Director Commissioner
Technical Services DivisionWorks and Emergency Services
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