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Workplan for Supplemental Investigation <br /> 2005 Navy Drive, Stockton, CA <br /> January 2, 2013 <br /> Page 9 of 12 <br /> 3.0 Proposed Site Investigation <br /> RBDI's proposed approach to further work at the site consists of the following <br /> iterative steps with our rationale provided for each proposed action as described <br /> below. <br /> 3.1 Soil Gas Sampling <br /> As described the report of groundwater investigation (KR Environmental, <br /> 12/10/2008), the contamination may have come from the former USTs or the <br /> existing wash rack (Figure 2). We propose to do multi-depth soil gas around the <br /> former USTs and wash rack area (KR Environmental, 2011). <br /> Nine locations are proposed as shown in Figure 5. At each location soil gas will be <br /> collected at two depths, 4 feet and 8 feet (bgs) using one liter Summa Canisters. <br /> The samples will be analyzed by Method TO-14 by Air Toxics Inc., a California State <br /> certified laboratory. <br /> 3.2 Grab Groundwater Sampling <br /> We propose to do a series of grab groundwater (GG) samples at depths similar to <br /> the shallow groundwater wells upgradient (northwest) of the former wells MW-1 and <br /> MW-2 which have consistently had DCE detected in groundwater samples. These <br /> sample locations are plotted on Figure 6. <br /> Initially, sample locations GG-1 through GG-9 will be collected from depths of no <br /> more than 25 feet bgs and analyzed for CVOCs using EPA Method 82608. If the soil <br /> gas data do not detect CVOCs and if these nine groundwater samples have DCE <br /> Risk-Based Decisions, Inc. <br />