In a Aug. 3, 2010 letter signed by Bae-Newplan Group Ltd. project engineer Keith Bartlett, it said data from a two-month observation period showed parts of the sewer system are “still at or over capacity during heavy rain events,” adding this is “especially true in the area of Peterson Drive including the 600 mm trunk sewer that services Beaverwood Treatment plant.”
Flow meters were installed at six locations throughout Gander’s sewer system and collected data from April 20 to July 1 – though one meter ceased recording data on May 8 due to a malfunction.
Three days during that period had high levels of precipitation, according to the report – May 4 at 41.6 mm, June 7 at 30.2 mm, and June 21 at 33.6 mm.
Flow data for May 4 showed the 600 mm trunk sewer was operating above its maximum capacity by four per cent and a further 12 per cent over design capacity.
The report noted that while no data was available June 7 for the 600 mm pipeline due to the meter malfunction, upstream flow meters setup at James Boulevard and the Cobham Street 450 mm and 600 mm pipelines had combined flow seven per cent greater than the combined flows on May 4. The report said this suggested “the 600 mm pipe from Peterson to the treatment plant could have been even further surcharged.”
“Another pipe would take some of the flow away from the existing pipe that’s there – there would be two pipes instead of one.” - Coun. Allan Scott
According to Environment Canada, 71 mm of rain fell on Aug. 23-24 and 54 mm on Aug. 30.
The report added that in order to make a recommendation, the full Gander system model Bae-Newplan is working on must be completed.
Last fall, the Town adopted a new bylaw prohibiting homeowners from having a direct or indirect connection from roof water downspouts to a building storm or sanitary sewer system. The Town previously estimated, based on a recreation of the events on Aug. 23-24, 2009, that roof runoff contributed to over 60 per cent of the capacity of the sewer main line on Peterson Drive and 27 per cent of the flows in the trunk main line.
Coun. Allan Scott, chair of the municipal works and services committee, said the preliminary report tells the Town there is a capacity problem. He said modelling work yet to be completed by Bae-Newplan should determine the size of the pipe necessary to meet capacity.
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