Ground-Water Quality in Kentucky: Nitrate-Nitrogen, by Philip G. Conard, Daniel I. Carey, James S. Webb, James S. Dinger, and Matthew J. McCourt, 1999

Nitrate (NO3-) is composed of the elements oxygen and nitrogen, and is an important source of nitrogen for plant and animal life; but too much nitrate in drinking water can be harmful to human health. Common sources of nitrate in water include plant and animal matter, human and animal waste, household septic systems, and fertilizers. Because it dissolves readily in water, nitrate from these sources is usually present at least in low concentrations in drinking-water supplies, regardless of the water source.

Utility companies that provide public water supplies test the water for concentrations of nitrate. This testing is much less common for private water supplies, however. More than 900,000 people in Kentucky use ground-water supplies, including approximately 500,000 supplied through public utilities and at least 400,000 using private wells or springs.

Excess nitrate in drinking water has been found to cause methemoglobinemia, or Blue Baby Syndrome, in infants less than 6 months old. The U.S. Environmental Protection Agency has established maximum contaminant levels (MCL's) for nitrate in public drinking water because of health concerns. The MCL for nitrogen can be expressed as units of nitrate (NO3-) or as units of nitrogen (N), referred to as nitrate-nitrogen (nitrate-N or NO3-N). The MCL expressed as units of nitrate is 45 milligrams per liter (mg/L). The MCL expressed as units of nitrate-nitrogen is 10 mg/L. Some laboratories use the term "parts per million" (ppm), which is essentially equivalent to mg/L in fresh water. Because most laboratories report nitrate as units of nitrate-nitrogen, that form of measurement is used in this report.

A map of the state shows the geographic distribution of nitrate-nitrogen concentrations, and a table shows the general trends of concentrations according to depth below the ground surface. Environmental scientists, engineers, and other professionals can use this information to gain an understanding of general trends in water quality that may be relevant on a regional or site-specific basis.