Ground-water quality, ground-water level, and rainfall data collected during the 1975 water year through the 1980 water year were analyzed to determine the effects of land application of effluent from wastewater treatment plants on ground-water quality in the Livermore-Amador Valley. Annual rainfall varied markedly during the study: 1976 and 1977 water years had less than one half the normal rainfall; 1978 and 1980 water years had greater than normal rainfall; and 1975 and 1979 water years had nearly normal rainfall. The direction ground-water movement in the valley was found to be generally that of surface water. Dissolved nitrate concentrations were generally much less in areas not receiving wastewater applications than in areas that do. Specific conductance, dissolved solids, dissolved chloride, and dissolved nitrate were substantially less in the lower aquifers than in the upper aquifer in the Livermore wastewater application areas. In the Castlewood, Pleasanton, Veterans Administration Hospital, and Livermore wastewater applications areas ground-water quality was similar to the quality of effluent from wastewater treatment plants in the valley. Rainfall, soil, and geology appeared to be the main determinants of ground-water quality in the Castlewood and Dublin-San Ramon and Camp Parks Military Reservation areas. Wastewater application appeared to be the main determinant of ground-water quality in Pleasanton, Veterans Administration Hospital, and Livermore Municipal Airport areas. Comparison of ground-water quality in wastewater application areas with proposed State water-quality objectives for ground water in the Livermore-Amador Valley showed impaired water quality in all areas.
