WATER CHEMISTRY AND NITRATE CONTAMINATION IN AQUIFERS IN LAGRANGE COUNTY, INDIANA

A project was initiated in 2002 to evaluate the chemistry and relative age of ground water in LaGrange County in northeastern Indiana. The intent of the 2002 sampling was to acquire baseline data by analyzing for selected ions, trace elements, and isotopes in ground water from 50 wells.

During a second phase of the project in 2003, water samples were collected from 18 additional wells containing ground water known to have high concentrations of nitrate nitrogen. The 2003 wells draw water from either sand and gravel deposits in the Topeka fan, Lima plain, and interlobate glacial sequences or localized sand and gravel deposits in the lacustrine Oliver Lake glacial sequence. The Topeka fan, Lima plain, and interlobate sequences are areas of ground-water recharge; the Oliver Lake basin is an area of ground-water discharge with areas of local recharge.

Nitrate nitrogen concentrations in the 2003 ground-water samples ranged from 7.0 to 30.4 mg/L. Seventy-two percent of the 2003 water samples had nitrate concentrations above the U.S. Environmental Protection Agency Maximum Contaminant Level of 10 mg/L. Nitrogen isotope values for these samples range from 4.9 to 22.3 parts per thousand (⁰/₀₀). The isotope values for samples from the 2003 wells in the Lima plain and Oliver Lake sequences range from 4.9 to 9.6⁰/₀₀ and show a positive correlation with sodium concentration. This suggests that the source of the nitrates in these two sequences includes septic waste. The nitrogen isotope values for 2003 samples from the Topeka fan sequence range from 5.3 to 22.3⁰/₀₀; sources of nitrates appear to include both septic and animal wastes.