MITIGATION AND COMPENSATION MEASURES FOR THE NECESSARY BUT HARMFUL ALTERATION, DISRUPTION OR DESTRUCTION OF FISH HABITAT – BAKER CREEK, GIANT MINE, NORTHWEST TERRITORIES, CANADA

Baker Creek drains a catchment area of approximately 126 square kilometres (49 square miles) on the north shore of Great Slave Lake near the city of Yellowknife. The catchment area is characterized by low relief, typical of the Canadian Shield and contains numerous lakes and wetland areas. The stream flow is primarily influenced by snow melt and flows normally peak in freshet during May and June. The lower part of the creek flows through the now abandoned and orphaned Giant Mine where creek sediments are contaminated with arsenic as a result of 50 years of gold ore processing.

A remediation plan being developed by the federal department of Indian and Northern Affairs Canada includes realignment of part of the Baker Creek channel within the mine site to move it away from underground arsenic storage chambers. In spring 2006, water leaking from Baker Creek through an open pit and into the underground mine created an emergency situation of potential mine flooding and possible release of arsenic contamination to the local water table. Consequently an emergency undertaking to realign Reach 4 and prevent the creek from flooding into the mine was initiated in May 2006 with engineering design and construction being completed within 4 months. The realignment was completed under a Fisheries and Oceans Canada authorization for works or undertakings affecting fish habitat. The authorization specified mitigation and compensation activities required for this undertaking. Compensation activities involved grading and shaping the reconstructed stream channel to provide approximately 2,100m2 (2511yd2) of long term natural stream channel with a mix of hydraulic habitats suitable for arctic grayling (Thymallus arcticus) spawning, rearing and overwintering habitats.

This paper describes the construction of the Baker Creek Reach 4 diversion and the first year results of habitat and physical performance monitoring of the new creek channel.