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OTTAWA — City staff suspect small amounts of sewage spilled from the Hemlock combined sewage overflow site into the Ottawa River earlier this month, but don’t yet know how it happened.
The suspected spills happened at the overflow site, beside the Hemlock sanitary sewage pumping station, over “several intermittent short-duration events” on May 11 and 12, resulting in a total of about 40 litres spilling into the river, wrote Dixon Weir, the city’s general manager of environmental services, in a memo.
The suspected spills were detected by temporary monitoring equipment installed as part of an ongoing study, Weir wrote. The cause of the suspected spills is being investigated, but it doesn’t appear at this point that rainfall would have been a factor, he wrote.
“Staff have implemented an enhanced level of site inspections given that our review of the sewers, in the area, do not indicate a cause or explanation of the recorded events,” Weir wrote.
The provincial Ministry of the Environment’s spills action centre and the public health branch have been notified, although staff can’t be certain of the amount spilled because the recorded amounts are at the limit of what instruments can reliably measure, according to Weir.
The suspected spills had no effect on drinking water, Weir wrote.
The suspected spills were followed by sewer overflows on Saturday of about 26 million litres of mixed raw sewage and rain into the Ottawa River, Weir wrote in a separate memo.
The spills action centre, public health branch and downstream water-system operators have been notified, according to Weir. All regulators are now working properly, he wrote.
Ongoing work is almost finished at the Cathcart, Rideau Canal and Keefer regulators (gates that trip when the sewage system is overloaded with rain) on a monitoring system meant to maximize the use of pipes before any sewage is released into the river. The work has already resulted in a lower volume of overflows into the river, according to Weir.
The formula used to come up with the estimated overflows hasn’t been adjusted to reflect the amount of sewage being directed to treatment by the new construction, so they are overestimated, the memo says.
Earlier this year, council approved a five-year, $251.64-million plan for an underground storage system intended to almost eliminate discharges of raw sewage into the river.
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