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NOA Drywell Closure and Investigation Page 20 of 26 <br /> May 30, 2014 <br /> 5.4 Discussion <br /> 5.4.1 Soil <br /> Environmental Screening Levels (ESL) were reviewed from the screening level guidance <br /> document published by the California Regional Water Quality Control Board — San Francisco Bay <br /> Region (December 2013). Values referenced were for deep soils (>10 feet bgs) at <br /> commercial/industrial sites where groundwater is a current or potential source of drinking <br /> water. These references and values were formed by the Regional Water Quality Control Board <br /> and are applicable to this site. <br /> ESLs are not regulatory cleanup standards, rather, they are conservative values that indicate <br /> the potential for adverse risk as a result of contaminants. Chemicals of Potential Concern <br /> (COPC) below the Commercial/Industrial Land Use ESLs can be assumed not to pose a <br /> significant threat to human health and the environment. For COPCs above <br /> Commercial/Industrial Land Use ESLs, further evaluation is warranted. <br /> The following COPCs were detected in some of the analyzed soil samples below their respective <br /> Commercial/Industrial Land Use ESL: Barium, Chromium, Lead and TPH as Diesel. These COPCs <br /> do not pose a significant threat to human health and the environment. The following COPC was <br /> detected in some of the analyzed soil samples at levels above its respective <br /> Commercial/Industrial Land Use ESL: Arsenic. Further evaluation of this COPC is warranted. <br /> The majority of soil samples contained elevated levels of Arsenic above the <br /> Commercial/Industrial Land Use ESL of 1.6 mg/Kg. The levels of Arsenic detected ranged from <br /> 0.82 mg/kg to 4.3 mg/Kg. Based on regional background soil sampling results from the United <br /> States Geological Survey (Wilson, S.A., et. al., Analysis of Soil Samples from the San Joaquin I� <br /> Valley of California, USGS Open File Report 90-214, 1990), the Arsenic levels do not appear to K. <br /> be elevated above typical levels for this region of California. Therefore, Arsenic is not a COPC. l bal <br /> No soil samples analyzed were impacted with COPCs. Most of the analytes detected in soil <br /> samples were metals. Based upon the above referenced USGS study performed by Wilson in - <br /> 1990, the metals detected in samples are at typical background concentrations for the San (, , D}C <br /> Joaquin Valley of California. One (1) sample collected at sixty (60) feet bgs from DW-2 /IF <br /> (B2@60'-II) contained 8.4 mg/L of TPH as Diesel. This level is below the Commercial/Industrial y��J <br /> Land Use ESL for this chemical. This sample was saturated and collected below the water table. <br /> 5.4.2 Groundwater <br /> Environmental Screening Levels (ESL) were reviewed from the screening level guidance <br /> document published by the California Regional Water Quality Control Board — San Francisco Bay <br /> Region (December 2013). Values referenced were for deep soils (>10 feet bgs) where <br /> groundwater is a current or potential source of drinking water. These references and values <br /> were formed by the Regional Water Quality Control Board and are applicable to this site. <br /> ESLs are not regulatory cleanup standards, rather, they are conservative values that indicate ` <br /> the potential for adverse risk as a result of contaminants. Chemicals of Potential Concern <br /> 902 Industrial Way• Lodi, CA 95240•209.367.3701 • Fax 209.333.8303 02014 Neil 0.Anderson&Associates,Inc. <br />