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1.0 INTRODUCTION <br /> Conestoga-Rovers & Associates (CRA) prepared this report on behalf of Equilon <br /> Enterprises LLC dba Shell Oil Products US (Shell) to document soil vapor sampling <br /> activities performed at the Former Shell Central Valley Pipelines, Neighborhood D, <br /> Mountain House, California (Figures 1 & 2). Collecting a soil vapor sample in the <br /> vicinity of the proposed Mountain House High School was recommended in the Central <br /> Valley Regional Water Quality Control Board (RWQCB) August 13, 2008 letter to Shell. <br /> Soil vapor well SVP-1 was installed during February 2009. <br /> 2.0 SOIL VAPOR SAMPLING <br /> CRA collected soil vapor samples from SVP-1 and prepared a soil vapor analytical data <br /> table (Table 1). The certified analytical data is included in Appendix A. The field data <br /> sheet is included in Appendix B. <br /> 2.1 SOIL VAPOR SAMPLING PROCEDURE <br /> SVP-1 has two screened intervals,one at 5 feet below grade (fbg) and one at 16 fbg. Soil <br /> vapor samples were collected from each screened interval and a duplicate sample was <br /> collected from the 5 fbg interval during this sampling event. In addition, a trip blank <br /> was prepared and analyzed. The soil vapor samples were collected from SVP-1 on <br /> July 15,2010 using the procedure described below. <br /> Prior to sampling,the weather was monitored to assure that no significant precipitation <br /> events occurred before the sampling event. No precipitation occurred prior to (within <br /> 72 hours of)the sampling event. <br /> During vapor probe sampling, the Teflon tubing for each vapor probe was connected to <br /> a control value, and then to a flow regulator attached to a lab-supplied sampling <br /> manifold connecting two 1-liter summa canisters (one purge canister and one sampling <br /> canister)with control valves and pressure gauges. Prior to sampling,a vacuum test was <br /> conducted between the summa canisters, the sampling manifold, and the valves by <br /> closing the valves, and opening the purge summa canister for approximately <br /> 10 minutes. During sampling, a containment unit (or shroud) was placed over the soil <br /> vapor probe surface casing,and helium gas was introduced into the containment unit to <br /> obtain a minimum 50 percent (%) helium content level. Helium meter readings were <br /> collected periodically during sampling, and helium was continuously introduced to the <br /> M02n(10) 1 CONESTOGA-ROVERS&ASSOCIATES <br />