A preliminary evaluation of the geohydrology and water quality of the Greenacres Landfill area, Spokane County, Washington

The Greenacres landfill, located about 11 miles east of the city of Spokane, Washington, was used for the disposal of waste from 1951 to 1972.Materials in the landfill include household and industrial waste materials, and various hazardous wastes.In 1983 the landfill was designated by the U.S. Environmental Protection Agency as a "Superfund" site.The purposes of this investigation were to gather, describe, and interpret all the existing data concerning the hydrology and ground-water quality of the area surrounding the landfill, and to identify any additional data needed to describe the hydrology of the area.The quantity of water flowing through the landfill as a result of precipitation on the landfill and in the drainage basin above the landfill probably ranges from 21,000 to 85,000 gallons per day.This water movement may be creating a leachate and transporting some of the wastes out of the landfill.If this is occurring, the leachate would flow into the Spokane aquifer, which underlies the lowest part of the landfill.A solute-transport model that simulates movement of conservative chemicals in the Spokane aquifer suggests that if leachate entered the aquifer it could form a contaminant plume extending west of the landfill.The plume would encompass an area where ground water provides most of the water used for municipal, industrial, irrigation, and domestic purposes.Water-quality analyses of water from numerous wells in the area which are open to the Spokane aquifer are available, but well 25/45-16K1 is the only well where ground-water contamination was consistently apparent.This well is only 500 feet from the landfill.Contamination of water in this well was indicated by high concentrations of dissolved mineral constituents and several organic compounds, including trans-dichloroethene in concentrations ranging from 115 to 392 micrograms per liter.Available data are insufficient to completely interpret the ground-water flow system near this well and the source of the contamination cannot be determined conclusively.While the existing data are adequate to provide background information, more data are needed to (1) determine the source of contamination in well 25/45-16K1, (2) determine ground-water flow in the Spokane aquifer near well 25/45-16K1, and (3) determine the extent of contamination in the Spokane aquifer.The degree of the influence of the landfill on the Spokane aquifer cannot be determined with existing data.Additional data acquired through the installation and monitoring of test wells for both water levels and specific chemical constituents will help answer these questions.