Ground water flow and chemical transport at a sodium sulfate disposal facility site, Owens Lake, California

The Owens Lake area of south-central California contains a dry playa lakebed that is characterized by upward ground water flow and subsequent evaporation at the lakebed surface. A sodium sulfate tailings disposal facility has been placed directly on top of the dry lakebed. Below the facility, the concentration of dissolved solids changes dramatically from 200,000 to 300,000 mg/L at the base of the tailings to about 20,000 mg/L at a depth of 10 feet below the tailings. Considering these unusual hydrochemical conditions, nontraditional analyses and field methods were used to characterize flow and chemical transport below the tailings. These included (1) installation of multi-level piezometers that provide point measurements of ground water pressure, (2) use of the pressure form of Darcy’s law to compute upward ground water flux, and (3) quantification of diffusion as the process which provides downward migration of chemicals in the presence of upward flowing ground water. The diffusion process is limiting, and calculations predict that the maximum depth of chemical migration will be 15 feet below the base of the tailings disposal facility.