Preliminary investigations of the geology, groundwater hydrology , and soil and groundwater 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 groundwater 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's.
The first wells drilled at each site were located to establish the direction of horizontal groundwater flow in each area. Groundwater 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 ft at the Pine County site and about 25 ft at the St. Louis County site. In addition, groundwater is perched seasonally at about 5 ft below land surface in the immediate vicinity fo the burial site in Pine County. After the direction of flow was determined, additional wells were drilled down-gradient from the disposal areas at both sites to determine whether contaminations were migrating with groundwater away from the sites.
In general, concentrations of lead and arsenic in soil and groundwater 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.
