Ground-Water and Soil Contamination Near Two Pesticide-Burial Sites in Minnesota

Preliminary investigations of the geology, ground-water hydrology, and soil and ground-water chemistry at sites in Pine and St. Louis Counties, Minnesota, have shown that contamination associated with pesticides buried at the sites is not widespread or highly concentrated. None of the pesticides sampled for in soil and in ground water at the sites exceeded Minnesota soil and drinking-water standards. About 1,500 pounds of lead arsenate were buried at the site in St. Louis County. Nearly 10,000 pounds of lead arsenate, as well as smaller quantities of organic pesticides (such as chlorpropham, DDT, endrin. and aldrin), lime sulfur, and magnesium carbonate were buried at the Pine County site. These chemicals were buried in shallow trenches at the sites during the early 1970 f s. The first wells drilled at each site were located to establish the direction of horizontal ground-water flow in each area. Ground water flows to the northeast at the St. Louis County site and to the southeast at the Pine County site. Depths to the water table are about 30 feet at the Pine County site and about 25 feet at the St. Louis County site. In addition, ground water is perched seasonally at about 5 feet below land surface in the immediate vicinity of the burial site in Pine County. After the direction of flow was determined, additional wells were drilled downgradient from the disposal areas at both sites to determine whether contaminants were migrating with ground water away from the si tea In general, concentrations of lead and arsenic in soil and ground water were below background concentrations for the areas. Concentrations of organic pesticides generally were below analytical-detection limits. The limited solubility of the chemicals and the tendency of the contaminants to be sorbed on soil particles probably combined to restrict mobilization of the chemicals.