USE OF DISSOLVED CHLORIDE CONCENTRATIONS IN TRIBUTARY STREAMS TO SUPPORT GEOSPATIAL ESTIMATES OF CL CONTAMINATION POTENTIAL NEAR SKIATOOK LAKE, NORTHEASTERN OKLAHOMA

Current and historic saline water produced from oil and gas wells potentially impacts surface-water bodies. The goal of this study is to assess impacts of saline releases to Skiatook Lake in Osage County, Oklahoma. About 6,715 oil and gas wells are located in the 350 mi² drainage basin that contains the lake and the 10,500 acres of land flooded by the lake (flooding began 1984) has approximately 215 plugged wells. The effect of the produced saline water (total dissolved solids >100,000 mg/L) on the lake was evaluated using a mass balance of concentrations of chloride in the inflowing waters draining into Skiatook Lake and correlating that with well densities in the various contributing drainages.

To provide a snapshot of current surface water inputs of Cl to Skiatook Lake, discharge measurements were made at the mouths of 18 streams draining into the lake, as well as the lake outfall. Chloride concentrations were measured at these sites, at 6 sites within the lake, and along the reaches of 2 of the streams that were observed to have high concentrations of Cl in a previous survey. Water in the lake has an average Cl value of 36 mg/L, with an estimated residence time of 18 months. Inflow from Hominy Creek, the major stream dammed by the lake, was 63 percent of the water entering the lake, draining an area representing 37 percent of the total drainage area of the basin that contains 44 percent of the oil and gas wells. Calculations indicate that almost 80 percent of the Cl load entering Skiatook Lake is from Hominy Creek. A mass balance calculation using the weighted average Cl concentration for all the other tributaries (17.8 mg/L), combined with the concentration of 44 mg/L Cl in Hominy Creek provided a reasonable match for the concentration of Cl (36 mg/L) in the lake. Geospatial analysis of well densities in subdrainages, also used to assess contamination potential, are compared to measured Cl values from the main streams in those areas.

Results indicate that a mass balance approach utilizing Cl concentrations coupled with geospatial analysis of well densities may be useful for assessing impacts of saline water releases to surface-water bodies.