ABSTRACTGround‐water quality, determined by 10 samplings of 14 wells within a 7.4 km2watershed during 1973–1982, was related to land use and geology. The wells represent forest and cropland use associated with three geologic zones. Nitrates, chloride and phosphate concentrations were much higher in ground waters underlying cropland. The mean concentrations ranged from five to seven times those observed in ground water underlying forests. The contamination pattern is consistent with that computed from a nutrient balance, based on known fertilizer and manure use on local croplands. Downgradient from the primary agricultural area, a geologic zone exists through which ground water from agricultural sources must pass to reach the stream. In this zone, the nitrate, chloride, and phosphate concentrations are greatly decreased due to mixing and dilution. The chemical nature of these ground waters reflects more the geochemistry of local geologic deposits than the impact of cropland use.A ground‐water flow system was hypothesized, based on known geologic, hydrologie, and geometric properties. The flow system is supported by the chemical