The Greenacres Landfill, located about 11 mi 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. EPA as a ' Superfund ' site. The purposes of this investigation were to gather, describe, and interpret all the existing data concerning the hydrology and groundwater 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 flow 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 gal/day. This water movement may be creating a leachate and transporting some of the wastes out of the landfill. The plume would encompass an area where groundwater 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 groundwater contamination was consistently apparent. This well is only 500 ft 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 (115 to 392 micrograms/L). Available data are insufficient to completely interpret the groundwater 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 groundwater 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. (Author 's abstract)