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Soil and Groundwater Investigation Report <br /> Mountain House Development Site#6 July 2008 <br /> SB-18 at depths ranging from 35 to 39.5 feet bgs. A source area has not been identified <br /> during field activities as evidenced by the absence of shallow affected soil. <br /> Affected groundwater has been delineated in the up-gradient direction;however, <br /> additional delineation is necessary in the cross-and down-gradient directions. It should <br /> be noted that in the down-gradient direction,benzo(a)pyrene concentrations detected in <br /> S13-7 are equal to the WQO screening levels of 0.0040 µg/L and can be used to <br /> adequately define the down-gradient extent of affected groundwater in this area. <br /> o Area 3 <br /> ■ Affected soil was only detected above the screening levels in borings SB-21 and S13-22; <br /> however,the borings located to the northeast do not adequately define the extent of <br /> affected soil due the shallow depth of soil sample collection. Soil samples were not <br /> collected from borings S13-1, S13-2, and S13-3 at deeper depths corresponding to where <br /> affected soil was detected in adjacent borings(SB-21 and S13-22). Therefore,the lateral <br /> extent of affected soil in the northeastern portion of the area is undefined. Field <br /> observations and laboratory analytical results concluded that the southeastern extent of <br /> the area has been defined by SB-27 through S13-29. The vertical extent of affected soil <br /> was defined in borings SB-21 and SB-22 at 27.5 and 31.5 feet bgs,respectively. A <br /> possible source area may be located around SB-22,where there was a TPHc detection at <br /> 24,000 mg/kg from a soil sample collected at 4.5 feet bgs. <br /> The affected groundwater in this area has been laterally defined; it should be noted that in <br /> the down-gradient direction, TPHd concentrations detected in SB-1 and SB-3 and <br /> dibenz(a,h)anthracene in SB-2 are slightly above WQO screening levels. These low <br /> concentrations are near the WQO screening levels and can therefore be used to <br /> adequately define the down-gradient extent of affected groundwater in this area. <br /> Additional investigation activities, as summarized in Table 8 and shown on Figure 4,will be implemented <br /> on acceptance by the RWQCB and securing site access and permits. <br /> 7. REFERENCES <br /> Ca1DHS, 2008. Title 22 California Code of Regulations California Safe Drinking Water Act&Related <br /> Laws and Regulation. March. <br /> Chevron,2006. HPP-BTR Waste Management Process. January. <br /> Condor,2001. Chevron Pipeline Easement Assessment Report-Mountain House, California, Volume I <br /> and 2. November. <br /> DWR,2003. California's Groundwater Bulletin 118, Update 2003. October(specific basin update <br /> January 20, 2006). <br /> EPA,2004. Region 9 PRGs Table. http://www.epa. ovg /region9/waste/sfund/prg/index.httnl#prgtable. <br /> October. <br /> Geomatrix,2005. Technical Approach to Site Evaluation and Decision-Making, Historical Pipeline <br /> Portfolio, Central Valley Region. February. <br /> RWQCB, 1998. Water Quality Control Plan (Basin Plan)for the Sacramento River Basin and the San <br /> Joaquin River Basin,4th ed. <br /> (Central Valley Region),2004. Beneficial Use-Protective Water Quality Limits for Components <br /> of Petroleum-Based Fuel. April. <br /> From Science to Solutions <br />