Grade A Dairy Farm Water Well Quality Survey

Abstract: The Wisconsin Department of Agriculture, Trade and Consumer Protection (WDATCP) estimated the proportion of wells on Grade A dairy farms that contain detectable levels of pesticides and nitrate-nitrogen (NO₃-N). A random sample of 550 farms was drawn from the population of 23,543 Grade A dairy farms. These farms were chosen because WDATCP has authority to collect water samples as part of its inspection program and because sampling this population should provide a meaningful measure of the presence of pesticides in groundwater in rural Wisconsin.

Water samples were actually collected from 534 of the 550 farms and analyzed for 44 compounds including 10 of the herbicides and 4 of the insecticides most commonly used in Wisconsin. One or more herbicides were detected in 71 wells. Sixty-four (64) of these contained atrazine alone, 3 contained alachlor (Lasso®) alone, 1 contained metribuzin (Sencor®) alone, 1 contained atrazine and alachlor, 1 contained atrazine and metolachlor (Dual®), and 1 contained alachlor and metribuzin. The maximum concentration of atrazine was 19.4 micrograms per liter (ug/l) with a median of 0.45 ug/l. The Entorcement Standard for atrazine of 3.5 ug/l was exceeded in 3 wells. The maximum alachlor concentration was 5.9 ug/l with a median of 0.7 ug/l. The Enforcement Standard for alachlor of 0.5 ug/l was exceeded in all 5 wells where it was detected.