Nitrate and Groundwater in Indiana:

Awareness needed but not alarm

Safe and abundant drinking water is one of Indiana's most valuable resources. More than 60% of the state's drinking water comes from groundwater (wells) and about half of this total comes from private wells. Overall, the quality of groundwater used for drinking in Indiana is very good and the vast majority of our residents have access to safe water. All public drinking water supplies in Indiana are tested regularly for bacterial and chemical contaminants, and are subject to federal health standards under the Safe Drinking Water Act. Less than 2% of public water supplies have had nitrate levels test higher than the drinking water standard, according to the Indiana Department of Environmental Management. Indiana citizens who get their water from public wells can be confident of the quality of their drinking water. Private wells, on the other hand, are not monitored by any government agency; therefore less is known about the quality of private water supplies and greater responsibility on the part of individuals is required.

One contaminant that has been found in some Indiana wells is nitrate. Nitrate is a health concern particularly for young infants, causing a sometimes-fatal condition called methemoglobinemia, or "blue baby syndrome". A recent news story suggested that miscarriages may also be linked to high nitrate levels, but further scientific study would be needed to establish a causal link. Because of the proven risk to infants under six months of age, however, any home with a private well where an infant is present or expected should have the well water tested and should use an alternative source if the nitrate level is above the drinking water standard. More information on the health effects of nitrates can be found here or in the Indiana Water Quality series WQ-5.

Some nitrate in ground water is due to naturally occurring sources, but levels of nitrate-N above about 3 parts per million (ppm) usually indicates contamination from a source such as septic systems, fertilizers (applied to lawns, golf courses, or agricultural areas), sewage sludge, or animal wastes. The EPA drinking water standard for nitrate-N, above which water should not be used by infants, is 10 ppm. Studies by the United States Geological Survey (1995) and the Indiana Farm Bureau Inc. (1994) in recent years found nitrate concentrations greater than the drinking water standard in 3.5% to 4.5% of private wells in the state. Although this is a serious concern for those households, particularly if an infant is present, more than 95% of private wells had water that is considered safe for nitrates. However all wells should be tested regularly to be sure of nitrate safety.

Contamination of groundwater depends on at least three factors:

  1. the vulnerability of the groundwater in the particular area to contamination,
  2. the well itself,
  3. the availability of excess nitrate leaching to groundwater.

    1. Groundwater vulnerability

    Groundwater vulnerability depends on a number of soil and geologic characteristics, including depth to the water table, texture of the soil, and bedrock characteristics. For example, groundwater underlying sandy soil is more vulnerable than groundwater under clay soils. Shallow groundwater is much more vulnerable than deeper aquifers. The vulnerability of the geologic area where the well is located is an important factor in determining risk of contamination.

    The map at left indicates the variability in aquifer vulnerability across the state. Geological areas that are highly vulnerable to groundwater contamination occur in north central and northwest Indiana, where soil is often sandy or gravelly, and in the valleys of all of Indiana's major rivers. Karst areas, where sinkholes provide direct access for potential contaminants to ground water, are also of concern. Areas underlain by glacial till or solid bedrock, including much of central and southern Indiana, are in general less vulnerable. Click here or on the map for more information about the prediction of groundwater vulnerability in Indiana.

    2. Well depth and construction

    Another important factor influencing contamination levels is the well depth. Shallow wells are much more likely to be contaminated than deep wells. In the Farm Bureau study of private wells, 12.2% of wells less than 50 ft. deep exceeded the drinking water standard, while only 0.9% of wells more than 100 ft.deep exceeded it.

    Contamination of a particular well can also depend on the well construction. In some cases, the top portion of the well is not adequately sealed when constructed, and contamination occurs around the top of wellhead.

    3. Potential sources of nitrate contamination

    Septic systems, fertilizer, and livestock wastes are all potential sources of nitrate that can leach to groundwater. It is usually difficult to assess the particular nitrate source when well water is found to be contaminated, since often the contamination is the result of the sum of many sources.

    Septic systems, especially if poorly constructed or maintained, are a potential source of nitrate and bacteria. Any well located near any part of a septic system (tank, sewer lines or leach field) is at risk for contamination. This risk is increased if the well is shallow, located in sandy or gravelly soil, located downslope from the septic system, or if the well and piping to the home is improperly constructed or maintained. The Indiana State Department of Health requires that septic tanks, dosing tanks, lift stations and soil absorption fields should be at least 50 feet from private wells, 10 ft. from water lines under pressure and 50 ft. from water lines continually under suction.

    Fertilizer and animal manures are also potential sources of contamination, and proper management practices are necessary to ensure that nitrogen is applied at the optimum rates and times for crop utilization so that excess nitrogen does not leach to the ground water. Indiana Department of Environmental Management requires that all approved livestock feeding facilities locate manure storages at least 100 ft. from wells and not apply manure closer than 200 ft. to a well.

    What we can do

    Groundwater contamination by nitrate above the drinking water standard is relatively rare in Indiana, but our generally high water quality should not lead to complacency. Potential nitrogen sources such as septic systems, lawn and field fertilizers, and animal manures must be carefully managed to minimize nitrogen that leaches into the ground water. All well water should be tested at least once per year. Even though the likelihood of detecting contamination is low, it's better to be safe than sorry.

    For more information, call the Agricultural and Biological Engineering Department at 317-494-1173 to obtain publication MWPS-14, Private Water Systems Handbook ($2.50)


    Wallrabenstein, L.K.,Richards, R.P., Baker, D.B.,and J.D. Barnett, 1994. Nitrate and Pesticides in Private Wells of Indiana. Indiana Farm Bureau Inc. and The Water Quality Laboratory, Heidelberg College.

    Risch, M.R. and D.A. Cohen, 1995. A Computerized Data Base of Nitrate Concentrations in Indiana Ground Water. USGS Open File Report 95-468.

    By: Jane Frankenberger
    Extension Agricultural Engineer
    Purdue University