Well Water Quality, Well Vulnerability, and Agricultural Contamination in the Midwestern United States

Abstract

The Heidelberg College Cooperative Private Well Testing Program is designed to evaluate water quality in private rural wells. The program inexpensively provides large datasets that reflect relationships between well contamination and associated factors, and support local groundwater protection and education programs. Nearly 35 000 wells have been tested in Ohio, Indiana, Illinois, West Virginia, and Kentucky. Median nitrate concentration was 0.07 mg/L ; 3.4% of wells exceeded the drinking water standard of 10 mg/L ; 23% exceeded 1 mg/L. Triazines were detected in 4.9% of 12 362 samples ; the atrazine MCL of 3.0 μg/L was exceeded in 0.1% of samples. Acetanilides were detected in 9.7% of 10 967 samples ; 1.1% exceeded the alachlor MCL of 2.0 μg/L. Many acetanilide detections, and most higher concentrations, are due to an alachlor breakdown product and involve little or no alachlor. Information supplied by well owners was used to examine the impact of cultural and geological factors on well water quality. Concentrations are higher in wells that are shallower, older, dug, or driven ; located close to cropland, feedlots, or chemical mixing sites ; or located in sandy soils. Where wells combine the most vulnerable alternative for two or three factors, the probability of contamination increases dramatically. Mapping sometimes reveals spatial patterns of contamination that reflect geological influences. River valley aquifers, sandy soils with high water tables, karst areas, and reef structures with surficial expressions are all reflected in county maps of the data.