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Mr. Maurice Benson <br /> November 3, 2008 <br /> Page 2 <br /> DTSC has reviewed the report and has the following comments: <br /> Comments: <br /> 1. Table 3-1, Soil Sampling Results; Soil sample analytical results indicate that <br /> contaminant levels for Trichloroethene (TCE) present in unsaturated soil <br /> suggest that Warehouse 10 is a continuing source of VOCs contamination to <br /> groundwater and will require additional remedial actions either in the form of <br /> soil vapor extraction or a soil removal action to eliminate the persistent source <br /> to groundwater. <br /> Specifically, the United States Environmental Protection Agency Region IX <br /> soil screening levels, referred to as dilution-attenuation factor (DAF) are <br /> exceeded at 14 of the 29 soil sample locations. At seven locations where the <br /> TCE DAF, of 0.003 mg/kg was exceeded in unsaturated soil samples, TCE <br /> contamination was recorded in groundwater above the cleanup level of 5 <br /> micrograms per liter (Ng/L). In addition, the 14 locations where the TCE DAF, <br /> soil screen levels were exceeded correspond to 12 locations with TCE <br /> concentrations in groundwater at more than the reporting limit. Moreover, the <br /> highest recorded concentration of TCE in unsaturated soil at CPT-23 <br /> collected at a depth of 7 feet bgs corresponds to the highest concentration of <br /> TCE in groundwater with a concentration of 32.8 pg/L, over six times the <br /> Maximum Contaminant Level. <br /> 2. Section 4.1, Conclusions; Soil Vapor concentrations in unsaturated soil <br /> indicate that soil vapor cleanup goals for TCE are exceeded at 17 of the 29 <br /> locations, with concentrations ranging from 430 to 15,000 parts per billion <br /> volume (ppbv). Prior to its demolition, Warehouse 10 was occupied by <br /> workers and office staff supporting DDJC-Tracy's mission. The high <br /> concentrations of VOCs currently present in the shallow unsaturated soil <br /> suggest that an indoor air contamination pathway was present for previous <br /> workers occupying Warehouse 10 and will be for any future building or facility <br /> constructed over the existing contaminated soil. Vapor intrusion modeling <br /> with risk assessment analysis will be necessary for any proposed structure or <br /> facility planning to be constructed over the existing contamination. <br /> 3. Section 4.2, Recommendations; The purpose of the Warehouse 10 <br /> Investigation Report was to summarize historical and recent fieldwork and <br /> present the data to the agencies to assist in the next course of remedial <br /> actions. Although DESJC is recommending a preferred remedial alternative <br />