The purpose of this investigation is to achieve regulatory compliance with the applicable ground-water monitoring requirements of the Resource Conservation and Recovery Act (RCRA) and the Washington Administrative Code (WAC). An assessment-level compliance monitoring project was established for the 183-H Basins because hazardous waste constituents were known to have entered the ground water beneath the facility. Three phases were defined for this project, with work being concentrated in five areas: geology, hydrology, ground-water monitoring, geochemistry, and ground-water modeling. These characterization activities have resulted in the definition of principal lithologic and hydrostratigraphic units. Ground-water monitoring results indicated a contamination peak, which occurred between April and August 1986. Further monitoring has shown that nitrate, sodium, gross alpha, and gross beta are the clearest indicators of ground-water contamination attributable to the 183-H Basins. In addition, the concentrations of these contaminants are affected by variations in Columbia River stage. Future studies will focus on continued ground-water monitoring throughout the closure and post-closure periods for the 183-H Basins, sampling of the Columbia River and nearby ground-water springs, and soil sampling adjacent to the facility. 45 refs., 90 figs., 19 tabs.