At 8 a.m., when starting his shift in a waste storage facility (landfill), a technician noticed the presence of leachate in a retention basin associated with leachate evaporation equipment. After having made sure no pollution had made its way off-site, pumps were used to collect the spilt leachate.

The low level of a leachate tank (used to supply leachate to the evaporators) had been reached during the previous night. This triggered a filling cycle, but the operation did not stop when the high level was reached. The leachate overflowed from the tank and filled part of the retention basin. The operator estimated that 31 m³ of leachate was released. The failure of the high-level sensor or an electrical micro-disconnection may have caused the event.

The inspection authorities for classified facilities went on site the following day and noted that despite the operator’s pumping operations:

• leachate was still present in the retention basin;
• leachate had seeped through the retention basin, indicating a loss of containment;
• puddles of leachate had formed in the land adjacent to the retention basin as well as in the site’s stormwater collection system;
• leachate was present in the peripheral drain header;
• significant seepage and traces of flowing were visible downstream from the header, heading directly into the natural environment.

The operator did not initiate any expert investigation or remediation measures following the event. The facilities continued to operate despite the absence of a diagnostic report of the malfunction that caused the release. A formal notice and an emergency measures order were issued requiring that the operator eliminate all releases of leachate into the natural environment. The operation of the leachate evaporators and all pumping into this unit was stopped until the corrective measures could be implemented. In the past, the site already experienced several leaks of leachate into the natural environment, particularly during wet weather. These incidences were not reported to the inspection authorities for classified facilities.

The operator undertook the following operations to prevent this type of accident happening again:

• the leachate evaporators are now shut down after the working day;
• a timer was installed on the tank filling pump so that it stops after each filling operation;
• the retention tank was rendered hermetic.