ARCHIVED REPORTS - GROUNDWATER MONITORING WELL INSTALLATION AND LIMITED SOIL SAMPLING

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1 KLEINFELDER The WQG for methylene chloride is 5 ug/1 and is also a PMCL. The detected concentrations of ' methylene chloride in each of the three water samples were 7.1 ug/l (MW-1), 33 ug/l (MW-2), and 15 ug/1 (MW-3). The concentrations of methylene chloride are shown to be higher in the upgradient water samples versus the downgradient sample suggesting an off-site source. Other VOCs detected included bromochloromethane (MW-2 only) with a concentration of 3.1 ug/l; and bromomethane (each well) with concentrations of 2.8 ug/1 (MW-1), 2.3 ug/1 (MW-2), and 2.7 ug/1 (MW-3). The WQG for bromochloromethane is expressed as a USEPA Suggested No Adverse Response Level (SNARL) for toxicity other than cancer risk of 90 ug/l. The WQG ' for bromomethane is also expressed as a SNARL with a level of 10 ug/1 (Draft level at this time form Cal EPA) and 9.8 ug/l as a USEPA Integrated Risk Information System (IRIS) Reference Dose as a Drinking Water Level (assuming 70 kg body weight, 2 liters per day water ' consumption, and 20% relative source contribution from drinking water). Bromochloromethane, which finds use in fire extinguishers, may be released to the environment as a fugitive emission during its manufacture, and during the use of fire extinguishers in which it is contained. ' Bromomethane, also known as methylbromide, is used as a soil fumigant, in refrigerants as well as some fire extinguishers. ' TPH-d and TPH-mo were detected only in the MW-1 sample (downgradient). The concentrations detected were 230 ug/1 and 280 ug/1 respectfully. The absence of either constituent noted in the soil samples collected from the 15' and 25' intervals of the MW-1 boring and the non-detectable ' concentrations noted from the soil boring samples and groundwater collected from MW-2 and MW-3 suggests the possibility of an on-site source upgradient of MW-1. Based on the findings of this assessment Kleinfelder recommends the excavation of affected soils for disposal off-site to a depth of approximately 2-feet in the areas of near surface lead contamination. Kleinfelder recommends the excavation of affected soils to a depth of 4-1/2-Feet in the area of the concrete pad(B-1, B-2, B-3) and the depth of approximately 6-feet near B-6 also indicated on Plate 3. The excavated soils should be disposed of at an approved waste facility ' designated to handle such waste. Confirmation soil samples should be collected and analyzed for TTLC and STLC concentrations ' from the bottom of the excavated areas of the site to determine if lead contamination reaches greater depths. Kleinfelder recommends that the soil cuttings generated from the installation of the monitoring wells and previously contained in 55-gallon drums and stored on site be emptied to the ground surface and spread on site as the soil sample analyses did not show levels of the detected ' concentrations at or above the applicable PRGs. Regulatory agency consent with this recommendation should be sought prior to dispersal of the drummed contents. ' A copy of this report should be forwarded to the San Joaquin County Environmental Health Department for their review and comment. ' 42162.E01 /ST04R854 Page 3 of 22 Copyright 2004,Kleinfelder,Inc. July 1,2004