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Evaluation of Ground Water in LaGrange County

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Nitrate in Ground Water

Introduction — Nitrogen (N) is a biologically active element involved in chemical reactions that are important to life and that affect water quality. Decaying plant and animal materials release organic nitrogen, which combines with oxygen and dissolves in water to form nitrate (NO3-1). Nitrate test results are expressed as either nitrate nitrogen (NO3-1-N) or as nitrate (NO3-1).

The nitrate-nitrogen data shown on the graph at left are from a database compiled by the LaGrange County Health Department. This database contains information about nitrate concentrations found in ground-water samples from some of the many water wells in the county. To collect the data, the health department made water-sampling vials available to interested individuals, who then filled the vials with water from their wells. These water samples were analyzed for nitrates and the results were sent to the participants and the health department.

Why is nitrate a concern? — The U.S. Environmental Protection Agency (EPA) has established a Maximum Contaminant Level of 10 milligrams per liter (mg/L) for nitrate nitrogen in drinking water. A condition known as methemoglobinemia in infants (blue baby syndrome) can occur when nitrate nitrogen concentrations in drinking water are above 10 mg/L. The nitrate interferes with the ability of infants’ red blood cells to carry oxygen to the tissues.

Spontaneous abortions (miscarriages) have been reported in women who drank water from nitrate-contaminated private wells. A report summarizing spontaneous abortions can be found on the Web site of the Centers for Disease Control and Prevention. Also, spontaneous abortions in livestock may occur when drinking water contains more than 10 mg/L nitrate nitrogen.

Nitrate Nitrogen Sources

What are sources of nitrate nitrogen in drinking water? — Potential sources of nitrate nitrogen in the ground water are inorganic nitrogen-based fertilizer, animal waste, decomposing crop residues, septic systems, and fixations of atmospheric nitrogen. The specific sources of nitrate nitrogen contamination can be identified by studying the proportions of stable isotopes of nitrogen. In the investigation of nitrogen isotopic signatures, two isotopes of nitrogen commonly are used: 14N and 15N.

Many people think that septic failure happens only when the absorption field plugs. This type of failure is not common in LaGrange County. In this county, most failures occur in septic systems that are completed in coarse-grained deposits, which are permeable and allow sewage to flow into the ground-water aquifer. Such failures can cause ground-water contamination.

Nitrate Concentrations—2002 Data

Nitrate concentrations — The nitrate nitrogen concentrations in the ground water sampled and analyzed in 2002 were generally low; 42 of the 50 samples had concentrations below the detection limit (less than 1 mg/L). Only one of the water samples had concentrations above the EPA Maximum Contaminant Level. Seven of the eight water samples containing measurable nitrate nitrogen were from wells in the Topeka fan glacial sequence. Nitrogen isotope values are used to identify the source of nitrates as either chemical fertilizer or of biological origin. Nitrogen isotope values determined for four sites ranged from 7.60 to 19.3 parts per thousand and indicate that the nitrate sources are largely animal or human waste.

Tritium Concentrations—2002 Data

Introduction — Tritium (3H) is an unstable radioactive isotope of hydrogen with a half-life of 12.43 years. It is produced naturally in low concentrations by interaction of cosmic rays with nitrogen and oxygen in the atmosphere. The most significant source of tritium is from the atmospheric testing of nuclear weapons from 1952 to 1969. Some traces of this tritium are still found in ground water. Tritium in the atmosphere is directly incorporated into the water molecule and is introduced to ground water through rainfall. Tritium is used to identify modern recharge to ground-water systems.

Tritium concentrations — In the water samples collected and analyzed in 2002, tritium concentrations ranged from below the detection limit (less than 0.8 tritium units) to 17.0 TU. Of the 50 samples, 35 had values above the detection limit. Tritium generally was not detected in waters from wells 100 feet or greater in depth. A tritium level greater than 2 TU is interpreted as being indicative of the presence of post-1952 recharge water (Fontes, 1980).

Conclusions

The prevalent chemical character of the ground water collected from 50 wells in the Topeka fan and Oliver Lake glacial sequences is dominated by calcium-magnesium bicarbonate. Of the inorganic chemicals measured, only nitrate-nitrogen from one well exceeded the current federal primary drinking water standards.

In regard to potential contamination, the nitrate data collected in 2002 suggest that the ground water in the Topeka fan area is more prone to man-made contamination from the surface. Tritium data suggest that the ground water in 60 to 70 percent of wells sampled in the Topeka fan and Oliver Lake areas in 2002 has been recharged since 1952.

The deposits of coarse sand and gravel in this region facilitate the rapid flow of ground water. Placement of new water wells should consider the locations of other facilities on the property such as septic systems or farm animal storage areas.

References

Brown, S. E., 1999, Part 2 — Ice marginal environments of Huron-Erie and Saginaw Lobes, north central Indiana, in Brown, S. E., Fisher, T. G., Kehew, A. E., and Taylor, L. D., Pleistocene geology of north-central Indiana and south-central Michigan, Guidebook for the 45th Midwest Friends of the Pleistocene Field Conference: Indiana Geological Survey Open-File Study 99-1, 77 p.

Centers for Disease Control and Prevention, 1996, Spontaneous abortions possibly related to ingestion of nitrate-contaminated well water—LaGrange County, Indiana, 1991-1994: Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report Web page, accessed on May 4, 2004.

Fleming, A. H., Brown, S. E., Smous, A. J., and Schrader, T. L., 1997, Glacial terrains of the Topeka, Shipshewana, Oliver Lake, LaGrange and Sturgis 7.5-minute quadrangles, LaGrange and Noble Counties, Indiana: Indiana Geological Survey Open-File Study 97-14, Expanded Explanation, 26 p.

Fontes, J. Ch., 1980, Environmental isotopes in groundwater hydrology in Fritz, P., and Fontes, J. Ch., eds., Handbook of environmental isotope geochemistry: Elsevier, Amsterdam, v. 1, p. 75–140.

Indiana Department of Natural Resources, Division of Water, 1987, Water resource availability in the St. Joseph River Basin, Indiana: Indiana Department of Natural Resources, Division of Water, Water Resource Assessment 87-1, 139 p.

U.S. Census Bureau, 2004, U.S. Census Bureau state and county QuickFacts—LaGrange County: U.S. Census Bureau Web page, accessed on May 4, 2004.

For additional information contact:

Nancy R. Hasenmueller (hasenmue@indiana.edu)
or
Tracy D. Branam (tbranam@indiana.edu)
Indiana Geological Survey
Indiana University
611 North Walnut Grove
Bloomington, IN 47405

Copyright © 2004, The Trustees of Indiana University