A 2 1/2-year study of the Columbia Plateau in Washington was begun in March 1982 to define spatial and temporal variations in dissolved sodium in aquifers of the Columbia River Basalt Group and to relate these variations to the groundwater system and its geologic framework. This report is part of that study and describes groundwater level contours for four major geohydrologic units in southeastern Washington, constructed from water-level data collected from approximately 1,100 wells during the spring of 1983, data from U.S. Geological Survey studies in the area, and other indirect methods. Configuration of the groundwater level contours is controlled by: (1) extent of a geohydrologic unit and geologic structure, (2) recharge from precipitation and surface water bodies, (3) rivers, lakes, and coulees that drain the groundwater system, and (4) hydraulic conductivities of each unit. Upgradient flexures of water level contours north of Connel, Washington, show effects of prolonged irrigation while downgradient flexures in an area south of Potholes Reservoir, in the vicinity of the East Low Irrigation Canal, show the effects of increased man-induced recharge. (USGS)
