A Compartment Model for 90 Sr Contamination in a Wetland at the Chalk River Laboratories

Abstract

Radioactive wastes originating from Canada's nuclear research and development program have been managed at the Atomic Energy of Canada Limited (AECL) Chalk River Laboratories (CRL) since 1946. In 1953 an area called Waste Management Area 'B' (WMA B) was developed to contain low and intermediate level solid waste (LLW and ILW respectively). Initially, all of the wastes were buried in unlined sand trenches or in asphalt lined trenches. These early trenches have been releasing strontium-90 (90Sr) to groundwater since 1954, resulting in an underground contaminant plume. A treatment system was constructed in 1994 and as a result the plume is being intercepted and treated for removal of 90Sr. Prior to the establishment of the treatment system the plume extended south and discharged into a watercourse called 'Spring B', then into a wetland area called 'West Swamp'. Routine monitoring of Spring B and the West Swamp outflows for 90Sr has been conducted since the 1960s. A compartment model of the West Swamp was developed and validated against monitoring data for Spring B. The purpose of developing the model was to determine if a standard compartment model could describe 90Sr dynamics in a wetland to support environmental decision making. The model employed mass balance calculations to describe the movement/distribution of 90Sr between the primary system compartments: water/peat, sediment, vegetation and litter. This paper describes how the compartment model was developed and validated. The model can be used as a tool to evaluate remediation alternatives and to provide input to CRL site decommissioning plans.