ENVIRONMENTAL IMPACT OF PRODUCED WATER AND HYDROCARBON RELEASES AT A LONG-TERM RESEARCH SITE ON SKIATOOK LAKE, OSAGE COUNTY, NORTHEASTERN OKLAHOMA

The USGS is investigating the impact of past oil production (1913-1973?) at a 1.5 hectare site adjacent to Skiatook Lake in northeastern Oklahoma. Produced water (PW) and hydrocarbon (HC) releases from surface pits, tanks, and broken pipelines have produced extensive soil and bedrock contamination whose dimensions are controlled by 1) the topographic position of two pits near a drainage divide; 2) the distribution, porosity, and permeability of surficial eolian sand, slope wash, and colluvium; and 3) the underlying gently dipping permeable sandstone and impermeable shale. A ground-water plume that intersects Skiatook Lake extends to depths of at least 8 meters and underlies a broad surface salt scar downslope north of the two pits. Total dissolved solids in the plume are as much as 35,000 ppm, with the presence of major dissolved Na and Cl confirming a PW source. Saline bedrock, as defined by electrical conductivity from ground geophysics and Cl-rich extracts of shallow core samples, extends several meters beyond the surface salt scar into the surrounding oak forest. Leaves of some oak trees near the salt scar show anomalously high Cl concentrations. Although the adjacent forested areas show colonization by blackjack and post oak during the mid-to-late 1900s, growth of these oaks was limited in the impact area where grasses, shrubs, and forbs dominate. Both degraded and undegraded oil from past HC production is present in pits and trenches. Oil-contaminated soil adjacent to pits and trenches contain microbial populations that are thermodynamically poised at the level of iron reduction.