Hydrogeochemical and mathematical analyses of aquifer intercommunication, Hanford Site, Washington state

The US Department of Energy Hanford Site in south-central Washington has served as an integrated nuclear facility since the early 1940s. Pleistocene postglacial flood waters and the ancestral Columbia River flowed through the center of the Hanford Site, carving erosional windows in the geologic unit that separates the two aquifers, thereby creating pathways for the migration to occur. A two fold research approach was applied to studying the problem: mathematical analyses of ground-water flow dynamics, and hydrogeochemical analyses of the ground waters. Data from tracer tests and water-level measurements in wells were used to define the ground-water flow system of the Rattlesnake Ridge aquifer. The hydrogeochemical data support the conceptual model of ground-water flow within the Rattlesnake aquifer. Interpretations of the various hydrogeochemical data indicate the same general pattern of mixing of unconfirmed aquifer waters in the Rattlesnake Ridge aquifer, resulting from aquifer intercommunication. Low levels (below drinking water standards) of tritium and iodine-129 in the Rattlesnake Ridge aquifer were identified in this mixing area. By applying a two-fold approach to the problem, a defensible conceptual model of ground-water flow and aquifer intercommunication within the study area was developed