A plume of saline water at the base of the glacial outwash aquifer near Vincennes, Indiana, has been drawn into the municipal well field. However, the average chloride concentration of the municipal water, 30 + or - 5 milligrams per liter, did not change significantly from 1976 to 1979. The plume , and elongated lens approximately 6,500 feet long by 1,500 feet wide, is 4 feet thick near the well field, and the chloride concentration of the water is 3,500 milligrams per liter. Half a mile to the west the thickness is 18 feet, and the chloride concentration is 5,100 milligrams per liter. The saline water seems to be entering the outwash aquifer through bedrock fractures near abandoned oil wells west of the well field. The fractures probably intersect unplugged intervals of the abandoned oil wells that convey saline water from bedrock aquifers at unknown depths. Digital model analysis indicates that doubling the 1978 pumping rate in the well field would cause water-levels declines of generally less than 8 feet. Solute-transport model analyses indicate that the chloride concentration of the well-field water would be less than 250 milligrams per liter for a saline-water intrusion rate ten times the model-calibrated rate. (USGS)
