At about noon, the operator of a non-hazardous waste storage facility raised the alarm after discovering an overflow on the leachate collection system.
The overflowing leachate had flowed by gravity:
- in part, directly into the storm drain. Contamination of clean water led to the death of several ornamental fish located there;
- in part, the ditch below the storage centre, which flows into the Riehbach River.
The fire brigade created earthen merlons as a defensive measure at the ditch’s outlet. An artificial basin, rendered hermetic by plastic sheeting (polyane film) was dug at the ditch’s junction with the stream to collect the contaminated water that had infiltrated into the ditch. The waters from the creek showed no evidence of visible pollution.
Contaminated water, confined in the ditch and in the storm drain, was pumped out and sent to a processing plant. The operator excavated and cleaned out the ditch. Given the storm warning in effect, the installations were monitored around the clock over the next few days.
Operation of the site in degraded mode following works led to the leachate overflow. A new lifting station is being built to improve leachate collection and treatment operations. During this work, one of the leachate collectors of the storage cell became plugged. Pumps were installed to pump the leachate into the storage area directly and to direct it to the dedicated basins by bypassing the pumping station being worked on. The system was supposed to be hermetic and withstand the pressure corresponding to the height of water between the bottom of the cell and the bottom of the network. A leak on a manhole between the cell and the storm drain was identified as the cause of the accidental release of leachates.
Following the accident, and to ensure proper leachate management during the rest of the construction phase, a lifting pump was installed in the leachate network on the leaky manhole to prevent the load on the network from increasing. In addition, the operator performs daily rounds, including on the weekends, and increases the frequency of rounds during rainy periods or after a storm.
