July 5th, 2018: The Inspector recommends closure of the spill file.

Subject: Follow-Up Spill Report – Spill of Greywater under Kitchen - Gahcho Kué Mine – March 28, 2018 (GNWT Spill # 2018-107) Incident Summary: At approximately 15:30 on March 28, 2018, a spill of approximately 300 litres of greywater was discovered under the kitchen at the Gahcho Kué Mine. The leak was noticed by a worker after receiving complaints of an odor emanating from an open access hatch during snow removal in the area. Upon initial investigation, it was discovered that a plastic (ABS) pipeline (drain pipe) used to convey greywater from the sinks and dishwasher in the kitchen to a lift station was broken, resulting in the greywater pooling under the kitchen trailer units. This pipeline is both heat-traced and insulated. It was discovered that the metal pipe hangers which are used to suspend the pipe were anchored to oriented strand board (OSB) only, instead of to more secure, solid wood floor joist (frame). This resulted in the hanger fasteners eventually pulling free of the OSB, causing the pipe to fall to the ground and break. Further investigation showed there was insufficient blocking to provide additional support to the pipe. The spilled greywater appeared to be entirely contained on the engineered gravel pad under the trailer, and there was no evidence that it had spread from the immediate area. Photos are attached. Immediate corrective actions implemented to control and remediate the spill included the following: 1. The water supply to the kitchen was shut off and locked out; 2. A vac truck was used to remove the pooled greywater from under the trailer, and dispose of it in the on-site waste water treatment plant; and 3. The broken pipe was replaced, the pipe hangers were attached to the wood floor joist, and wooden blocking installed to provide additional support to the pipe. Based on the volume of greywater removed by the vac truck immediately following the discovery of the spill, it is estimated that the total volume of spilled material was approximately 300 litres. An NT-NU Spill Report was completed and submitted via email to the NWT Spills Hotline (spills@gov.nt.ca) at 13:38 on March 29, 2018. Root Cause Analysis: The results of an internal De Beers investigation determined that the cause of the spill was improper fastening of two metal pipe hangers to insecure material (oriented strand board), which failed to support the weight and caused a section of the pipe to drop to the ground and break. Corrective Actions: The following additional measures have been implemented to mitigate the effects of the spill and prevent a recurrence: 1. Lime was spread over the affected area to limit microbial growth and eliminate odours in order to reduce the potential to attract wildlife. This action was completed on March 29; 2. The damaged section of pipe, along with the failed pipe hangers, were replaced, and the pipe was re-suspended off the ground, with the hangers attached to secure wood floor joist. This action was completed on March 28; 3. Additional blocking was installed to provide additional support beneath the suspended pipe. This action was completed on March 28. The internal investigation relating to this incident has been concluded and the corrective actions complete.