RCRA Investigation of Former Refinery Site Casper, Wyoming

For a RCRA Facility Investigation (RFI) of this former BP-Amoco refinery, SSP&A provided technical support in geochemistry, groundwater, and geology, and participated in Collaborative Process meetings with Wyoming State agencies regarding Soda Lake, a former discharge point for refinery effluent. SSP&A's initial activities involved the development of a site conceptual model of groundwter for the Soda Lake region; siting of numerous groundwater-monitoring wells in both Cretaceous sedimentary formations and unconsolidated sandy soils; evaluation of the water balance and selenium biogeochemical cycle in the lake; and, development of a probabilistic model for predicting future selenium concentrations in lake water and sediments under different management alternatives.

Soda Lake was found to be a classical discharge lake, with a deeper groundwater underflow component. A goal of the RFI was to demonstrate how the Remedy Decision data were of sufficient quality and quantity to evaluate the nature and extent of contamination present or probable at the site and to support a Risk Assessment and a Corrective Measures Studies. Based SSP&A’s studies, the shallow groundwater flow system was found to discharge from the total lake periphery into Soda Lake, which lies in an enclosed basin. No groundwater was found to migrate down-gradient toward the North Platte River. This conclusion was based on (a) SSP&A’s water-balance modeling, which demonstrated that all water loss from the Soda Lake basin is via evaporation; (b) groundwater contour maps and hydrographs documenting that groundwater flows radially into Soda Lake; and (c) chemical analyses of groundwater and lake water indicating that net groundwater flow is toward Soda Lake.

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