Clark Island is a 63 ha island located in Lake St-Francis, part of the St-Lawrence River, Québec, Canada. Since the early 40s the island has been used for the production of mineral acids by its fanner owner, Allied Chemicals Limited. Acidic wastes were placed over large portions of the island. The presence of these waste materials together with contaminated soils was identified as a potential threat to the nearby river water quality as well as to the underlying bedrock groundwater quality. A major remedial investigation and feasibility study was initiated in 1987. The approved scope of the remediation project included the construction of one 60,000 m3 single lined cell for the placement of contaminated soils, and one 130,000 m3 double lined cell for the placement of acidic wastes. The remediation project was implemented during the 1991-1993 period. In order to assess the efficiency of the remediation, a detailed environmental monitoring program was implemented during the works and in the following years. The general conclusion of this major project is that confining acidic wastes in lined cells provide a safe and economical way to avoid detrimental consequences to the environment
