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Groundwater Mystery Solved

You might think that abandoned animal feedlots are of little consequence to our environment and health. If so, you'd be wrong.

Researchers from the Kentucky Geological Survey and College of Agriculture at the University of Kentucky have identified such feedlots as a source of high concentrations of nitrate-nitrogen (nitrate-N) in rural groundwater supplies in Western Kentucky. Human sewage, livestock manure and chemical fertilizers are sources of nitrate-N contamination in groundwater.

Excessive levels of nitrate-N in drinking water can cause sickness in humans and livestock, and it's even possible to die from drinking water too high in nitrate-N. Infants less than 1 year old and pregnant women are particularly at risk.

Animals in feeding and holding lots create a compacted soil layer. The compaction, combined with swelling wet manure, usually prevents downward movement of nitrate-N to the water table. After the lot is abandoned, however, the manure and soil dehydrates and cracks over a period of years. And once surface cracks form, rainfall can move through the soil and transport nitrate-N to the water table.

So far, UK researchers have identified three abandoned lots as high-volume purveyors of nitrate-N, and nitrogen isotope samples indicate that the nitrate-N was derived from livestock manure. One of the three abandoned lots is located in Henderson County. The domestic water supply at this site contains 45 mg/L nitrate-N—four-and-a-half times the maximum contaminant level (MCL). The MCL established by the U.S. Environmental Protection Agency for nitrate-N is 10 milligrams per liter (mg/L).

Glynn Beck and James Dinger of the Kentucky Geological Survey, and John Grove and Eugenia Pena-Yewtukhiw of the UK College of Agriculture have devised a remedy. After doing geostatistical modeling of nitrate and organic matter data from more than 100 soil cores collected from abandoned lots, the researchers removed portions of the organic-rich soil from the lot and spread these on a nearby pasture. The excavated area was then backfilled with native soil and leveled.

The results to date are encouraging: the nitrate-N concentration in groundwater beneath the center of the feedlot continues to drop and is currently 118 mg/L, a considerable decrease from 145 mg/L prior to remediation one-and-a-half years ago. Prior to this project, very little research had been done to assess the impact of abandoned feeding and holding lots on the environment.