FINAL REPORT - International Joint Commission

Determining a critical elevation for plan performance measures for residential systems is difficult given that
little documented data exist. However, based on available information, a flurry of complaints from Thousand
Islands area residents were filed with Environment Canada in the fall and winter of 1998, and other reports
were documented near Massena, New York, during the same time period. Reports were also received in
November of 2002 from U.S. residents in the Thousand Islands area. Furthermore, most reported problems
from the August 2003 shore well survey appear to have occurred from 1998 onward. At the time the
reports occurred, Lake Ontario was at its lowest level in 30 years—a monthly average in November 1998
of 74.40 m (244.03 ft). In 2002, when other reports surfaced in the same geographic area, lake levels
were only slightly higher than in 1997—74.46 m (244.30 ft). Therefore, based on available information,
a lake elevation of about 74.37 m (244.00 ft) could serve as plan performance measure for shore wells
along Lake Ontario. Along the upper St. Lawrence, substantial problems with water levels and lake intake
lines were reported beginning in August of 1997 and throughout 1998 along Lake St. Lawrence. Longterm
historical data for Lake St. Lawrence (e.g., the Long Sault gauge) were not available at the time this
report was written, but the above dates could serve as a reference point for selecting an appropriate
critical water level.
ANNEX 2
PMCL advertised in local papers asking people if they had problems withdrawing water from the River, and
the few responses received indicated that people fixed any problems themselves. The Wilson Hill community,
which had been affected by this problem, has since obtained municipal water supplies. Although the
economic impacts associated with this phenomenon could not be quantified, it was tracked to see how
reliably each plan produced water levels above the elevations at which such problems were said to begin.
Lower St. Lawrence River
Municipal and industrial intakes
Based on the survey results, the main problems experienced by water utilities are taste and odour, frazil ice
and capacity. Taste and odour and frazil problems are not necessarily directly related to low water levels in
all cases but tend to increase in such conditions, according to utilities. A total of 42% of the utilities suffer
from taste and odour problems, while 50% experience frazil problems. Capacity limitations in low water
levels were mentioned by three utilities out of 30.
The impacts of low water levels on plant operation were characterized by red and yellow production
performance indicators. The red production performance indicator describes a severe consequence
corresponding to the water level at which a plant will no longer be able to supply nominal capacity using
the available infrastructures (i.e. pumping stations and water intakes). Alternatively, the yellow
performance indicator describes the water level at which a plant will need to open its emergency intake to
supply nominal capacity (i.e., modify its normal operating condition). This performance indicator therefore
represents an alarm sign indicating that the nominal capacity of the plant can no longer be maintained by
the principal intake. A yellow performance indicator could only be determined for plants disposing of more
than one intake.
The critical water levels (red performance indicator) for each plant downstream of Ste-Anne-de-Bellevue
are summarized in Figure F-1.
With respect to the red production performance indicator, the plants that are the most affected by water
levels are: Lavaltrie, Montreal (Atwater and DesBaillets), Verchères, Pointe-Claire, St-Lambert and Candiac.
These seven systems will reach the red production performance indicator at water levels above the worst
case scenario studied, which is 1.0 metre (3.3 ft) below the chart datum at Pointe-Claire (70 cm (28 in)
below the historical minimum level). These plants represent 23% of the plants investigated (7/30) and
more than 74% of the population of the study area (1,720,000/2,320,000). The Varennes WTP would see
its normal operating conditions restricted (yellow PI) under the worst water level scenario considered.
Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows
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