REMOVAL OF CONTAMINANT SALT FROM A DEPLETED
PETROLEUM FIELD BY RUNOFF: RESULTS FROM THE
OSPER "A" SITE, OSAGE COUNTY, OKLAHOMA
Yousif K. Kharaka
U. S. Geological Survey
345 Middlefield Rd.
Menlo Park, CA 94025
A multidisciplinary group of ~20 scientists are investigating the transport, fate, natural attenuation and ecosystem impacts of inorganic salts, organic compounds and radionuclides present in releases of produced water and associated hydrocarbons at the Osage-Skiatook Petroleum Environmental Research (OSPER) sites, located in Osage County, Oklahoma. Results from repeated sampling of 44 wells from the depleted OSPER "A" site show that the contaminant salts have been leached from the soil and surficial rocks, but that a plume of high salinity groundwater (2,000-30,000 mg/L TDS) with BTEX and other VOCs, extending beyond the 1.2 hectare visibly impacted area is present at intermediate depths. This plume intersects the surface at the lower, steeper, more heavily salt-impacted northern portion, which has been eroded to depths of as much as 2 m. It also intersects the adjacent Skiatook Lake, a 4250-hectare reservoir that provides drinking water to the local communities and is a major recreational fishery.
A weir and an automated precipitation gauge were installed close to the Skiatook Lake to investigate the natural overland transport of salts from this site by measuring the volume and chemical composition of surface runoff from precipitation events draining a 1.7-hectare area. Results to date show that the initial runoff that leaches the previously precipitated surficial salts can have a relatively high salinity (up to 3,000 mg/L TDS), but that only small amounts of total salts are removed by this process. This result supports the conclusion that large amounts of salts from produced-water and petroleum releases still remain in the rocks of the impacted area after more than 65 years of natural attenuation.