Quality of water in the alluvial aquifer and tributary alluvium of the Fountain Creek valley, southwestern El Paso County, Colorado, 1991-92

The alluvial aquifer in Fountain Creek Valley between Colorado Springs and Widefield is the source for several public water-supply systems. Since 1981, concentrations of dissolved nitrite plus nitrate as nitrogen (nitrate) have exceeded the drinking-water standard of 10 milligrams per liter in several areas of the aquifer. Water-quality data collected quarterly from August 1991 through October 1992 from a network of 63 wells were used to define the spatial and temporal variability of dissolved- oxygen, dissolved-solids, major ions, and nitrogen concentrations in the aquifer. Ground water generally was well oxygenated in the main body of the aquifer, but anoxic conditions occurred near the interface of the aquifer and Fountain Creek. Dissolved-solids concentrations generally were larger, and nitrate concentrations generally were smaller near Fountain Creek than in the main body of the aquifer. Dissolved-solids concentrations generally decreased and nitrate concentrations generally increased with distance from the creek. Ground-water flow toward Fountain Creek and relatively small dissolved-solids concentrations in the main body of the aquifer indicated that the primary source of recharge to the aquifer was surface recharge from precipitation and lawn irrigation. Natural soil nitrogen, lawn fertilizers, and leakage from industrial-waste lagoons seem to be major sources of nitrate in ground water.