LeMasters, Gary S.; Doyle, Douglas J. / Grade A dairy farm well water quality survey
Introduction, pp. 1-2 PDF (660.9 KB)
INTRODUCTION In 1985 Wisconsin farmers were reported to have used about 5.2 million pounds of atrazine (a herbicide used primarily to control broadleaf weeds in corn) and 3.4 million pounds of alachlor (Lasso*, a herbicide used primarily for grass control in corn) on about 5 million acres of corn (WDATCP, 1986). At about this time the Wisconsin Department of Agriculture, Trade and Consumer Protection (WDATCP) began a monitoring program to determine if agricultural chemicals were reaching groundwater in significant concentrations. Shallow wells were installed at the water table immediately downgradient from agricultural fields that featured sandy soils, shallow depth to groundwater, and irrigation. Among the most frequently found compounds in this program were atrazine and alachlor. At this time Wisconsin had not adopted any official groundwater standards for these compounds and the unofficial guideline concentrations were not being exceeded. In 1988 the Wisconsin Department of Natural Resources (WDNR) adopted health-based groundwater standards for atrazine and alachlor which were significantly lower than the unofficial guidelines. While the monitoring program showed that these compounds could reach groundwater at levels above these new standards in susceptible areas, no reliable information was available about the statewide extent of groundwater contamination from these compounds. The Grade A Dairy Farm Well Water Quality Survey reported herein was designed to meet this need. The survey was funded with pesticide research fund monies collected by the Agricultural Resource Management (ARM) Division of WDATCP, and by a grant from the WDNR. All samples were collected between August, 1988 and February, 1989. A total of 534 wells on Grade A dairy farms were sampled. Throughout the report the concentration of a pesticide is expressed in units of micrograms of active ingredient per liter of water, abbreviated ug/l. This is the preferred unit for expressing a concentration of a pesticide in water, and is equivalent to the more familiar unit of parts per billion, abbreviated ppb. The concentration of nitrate + nitrite as nitrogen is expressed in units of milligrams of nitrate + nitrite as nitrogen per liter of water, abbreviated mg/l, which is the equivalent to parts per million. Nitrite concentrations in groundwater are usually insignificant so throughout the report the abbreviation N03-N will be used to denote both the nitrate and nitrite forms of nitrogen.