L.S. Seigley(1), G.R. Hallberg(1), P.R. Walther(2), and G.A. Miller(3)

(1)Iowa Department of Natural Resources, Geological Survey Bureau, 109 Trowbridge Hall, Iowa City, IA 52242-1319
(2) 916 E. Broadway, Audubon, Iowa 50025
(3) Iowa State University Extension, 2104 Agronomy Hall, Ames, IA 50011
Journal of the Iowa Academy of Science v. 100 (1), p. 15-20


This study presents the results of a countywide volunteer sampling of private well-water. Volunteers collected 231 well-water samples in Audubon County for nitrate-nitrogen (nitrate-N) and total coliform bacteria analyses during September 1988. Questionnaires were completed at all sites to document well construction, age and depth of well, well placement relative to septic system, barnyard/feedlots, location of chemical mixing/tank rinsing, and presence of abandoned wells.

The majority of the wells were large-diameter "seepage" wells; 67% were less than 40 feet (12 m) deep. Seventy-eight percent of the samples were positive for total coliform bacteria. Twenty-four percent of the samples were from wells using cisterns; 93% of these samples tested positive for total coliform bacteria. Twenty-six percent of the wells had nitrate-N concentrations greater than 10 mg/L. Mean nitrate-N concentrations and bacteria positives decreased with increasing well depth. There were no obvious widespread point source problems. The majority of wells were greater than 100 feet (30 m) from an active barnyard/feedlot and greater than 50 feet (15 m) from a septic system; 92% were greater than 50 feet (15 m) from chemical mixing locations. Wells closer to septic systems and feedlots actually showed lower proportions of high nitrate and bacteria positives than those farther away. Seventy-seven abandoned wells were reported; 68% were less than 40 feet (12 m) deep. The nitrate-N and total coliform bacteria results from this large number of observations across the entire county are similar to water-quality results from more detailed, smaller-scale watershed studies within the county.