SITE INFORMATION AND CORRESPONDENCE

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Ms. Wendy L. Cohen, Chief - 2 - 5 March 2003 Cleanup Goals Attached to this memorandum is a table of designated levels that defines cleanup goals for soil contaminants and groundwater pollutants. The designated levels for soil are derived by identifying the appropriate water quality limit and back-calculating the concentration of contaminant that could remain in soil and not present a threat to water quality. A leachability factor and an attenuation factor are ascribed to each constituent based on the tendency of a constituent to migrate with water (the leachability factor) and the capacity of the soil column to accommodate constituents (the attenuation factor). The attenuation factor takes into account the 30-foot depth to groundwater and the unsaturated zone soil types encountered at this site (predominantly silty clay, clay, and sandy clay). The designated level is calculated by multiplying the water quality limit, leachability factor and attenuation factor. If there is less than 10 feet of soil above the water table, the attenuation factor is reduced by a factor of 10, and a corresponding designated level is derived. The cleanup goal for nitrogen compounds in soil for most of this site is 250 mg/kg for the sum of nitrate and ammonium, based on the distance to groundwater. For the areas of the old tank farm and the northern area in which these compounds extend to the water table, the cleanup goal becomes the detection limit for the sum of these compounds within 10 feet of the water table. Alternatively, if WFS wishes to show that a higher concentration of nitrogen in soil in proximity to the water table will not affect water quality, it may analyze soil containing known quantities of nitrogen with a waste extraction test using de-ionized water as the extractant(DI-WET). If WFS chooses to pursue this method of determining a cleanup goal for nitrogen near the water table, it should discuss the procedural details with us first. Nitrate in groundwater upgradient of the site occasionally exceeds the water quality limit of 10 mg/l nitrate-as-nitrogen, as evidenced by concentrations observed in upgradient monitoring wells MW-1 and MW-4, which have fluctuated from 8 to 22 mg/l between March 1998 and August 2002. The variation in the monitoring data suggests that slugs of nitrate occasionally pass by from upgradient sources. The cleanup goal for nitrate in groundwater will be based on an assessment of background concentrations as measured from these two upgradient wells. Distribution of Pesticides in Soil At this facility, pesticides have always been stored as packaged products, applied in the field, and the application equipment rinsed in the rinse pad area, according a 13 February 2003 phone conversation with Ms. Bishop. The pesticide analyses of the 1990 Investigation were conducted on 29 soil samples from 11 borings in areas where equipment and products were stored or rinsed, or where soil staining was observed. The pesticide analytical suites included organochlorine compounds, organophosphate compounds, volatile organic compounds, carbamate/urea compounds, and chlorinated herbicides. This investigation showed that the primary source area for pesticides is in the northern corner of the site, which houses the rinse pad, one of two former dry wells, and a stormwater ponding area. The stormwater ponding area, immediately downgradient from the rinse pad, is the location of the HRC® pilot test. WFS searched for the dry well as reported in GeoSyntec's 23 December 1998 Results of Geophysical Survey to Locate Reported Dry Wells, but a dry well was not identified. Soil samples obtained to a depth of 10 feet bgs at the stormwater pond contained dinoseb and 1,2-DCP, and samples obtained to 6 feet bgs at the rinse pad contained diuron and ammonium. At the dry well, samples were obtained to a depth of 24 feet bgs, and diuron, dinoseb, 1,2-DCP, and dibromochloro-