The partitioning of iodine-129 in a shallow sand aquifer: Chalk River, Ontario.

Abstract

129I is a fission product with a long half-life (1.57 x 107 yrs) that has important implications as a tool to monitor long-term stability and interactions in the hydrosphere, biosphere and geosphere. In the groundwaters, migration of 129I, which because of its low natural concentrations is assumed to be the same as stable iodine (127I), can be retarded by various reactions with geologic and biologic reservoirs. At Atomic Energy of Canada, Chalk River Laboratories, Ontario, solid, low-level radioactive wastes from industrial, academic and medical applications have been stored in trenches overlying unconsolidated sandy glacial tills and permeable very-fine to fine-grained sands overlying crystalline bedrock. The sandy aquifer system drains into a Swamp comprised of approximately 3 in of sphagnum peat. Hydrologically, most of the yearly precipitation (∼340mm/a) percolates into the underlying aquifer at Area C. This has generated a contaminant plume, having chemical characteristics of a dilute, sanitary landfill leachate, containing 14C (DOC, DIC), tritium (HTO) and levels of 129I which are elevated above present-day precipitation levels of approximately 107 atoms 129I/l water. A comprehensive field and analytical program at this site has been initiated to examine the partitioning of 127I and 129I amongst the various reservoirs in this system and the controlling factors. (Abstract shortened by UMI.)