Hydrogeology and ground-water-quality conditions at the Sumner County Landfill, south-central Kansas, 1989-90

Abstract

An investigation of the geology, hydrology, and water quality at the Reno County Landfill, south-central Kansas, was conducted from August 1990 to March 1991. In the vicinity of the landfill, the Ninnescah Shale of Permian age constitutes the bedrock surface and is overlain by Quaternary sand-and-gravel deposits. Overlying the sand and gravel is a clay or silty clay layer, which in turn is overlain by top soil. The sand-and-gravel deposits are between 100 to 140 feet thick. The thickness of the clay or silty clay layer varies, increasing to about 50 feet south of the landfill. Salt Creek is located directly north of the landfill and was a losing stream during the investigation. Potentiometric-surface maps constructed from measured water levels in temporary, monitoring, and industrial-observation wells indicated that ground-water movement is from west to east parallel to Salt Creek and the Arkansas River. The average linear velocity of the ground water was calculated to be 0.75 foot per day. Chemical analysis of water samples from monitoring wells, supply wells, and Salt Creek at and in the vicinity of the Reno County Landfill indicates large concentrations of chloride. These large chloride concentrations contribute to larger specific-conductance values and dissolved-solids concentrations in ground water with increased proximity to Salt Creek. Leachate from both the old city and the old county sections of the landfill is the probable source of large iron and manganese concentrations in wells located on the landfill property. Dissolved organic carbon, methylene-blue active substances, and 23 specific organic compounds were detected in water samples from the monitoring wells. Concentrations of 1,1-dichloroethane, tetrachloroethylene, trichloroethylene, and vinyl chloride in water samples from wells on the landfill property exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level (for drinking-water supplies). The extent of downgradient movement of the organic compounds is not known, but compounds are suspected to migrate east of the landfill in the direction of ground-water flow. From previous sampling, organic compounds were detected in water from private-supply wells east of the landfill. During the investigation, organic compounds were not detected in downgradient wells MW-11, PW-2, or PW-5, and only small concentrations were detected in downgradient wells PW-3 and MW-14. Analyses of samples from these downgradient wells can be used to outline a nondetectable limit or boundary for organic-compound migration. The vertical extent of the leachate plume may be approaching bedrock, as indicated by concentrations of 1,1-dichloroethane, 1,2trans-dichloroethylene, trichloroethylene, and vinyl chloride in water samples from well MW-12. Concentrations of organic compounds in ground water decrease in the direction of ground-water flow, probably as a result of degradation, dispersion, and dilution.