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Lee Higgins -2- 6 August 2010 ' <br /> Chevron, Mountain House Site#6 <br /> ri <br /> ri 1 <br /> 600 feet long. Both affected areas occur primarily beneath West Byron Road, elongated <br /> parallel to and within/beneath the former OVP/TAOC alignment. The vertical extent of affected <br /> soil at the Site was defined by ND analytical results for TPH for samples collected in borings at ' <br /> depths of 33.5 to 39.5 feet below ground surface (bgs). <br /> The outline of affected groundwater in Area 1 is slightly larger than affected soil, with , <br /> approximate dimensions of about 120 feet by 225 feet. Within Area 2, there are two separate <br /> areas of affected groundwater, with irregular shapes of approximately 200 by 250 feet and 300 <br /> by 350 feet, respectively that overlap/coincide with the southeast and northwest ends of the ' <br /> Area 2 affected soil. TPHc in soil was detected in soil at depths of 20 to 22 feet bgs at <br /> concentrations of 230 to 6,900 mg/kg; deeper samples obtained from a depth of 26 feet bgs <br /> reported TPHc concentration at 5.3 mg/kg, ' <br /> The vertical extent of affected groundwater was defined by ND results for a water sample from <br /> a depth of 35 feet bgs. The depth to uppermost groundwater is approximately 6 to 10 feet bgs. ' <br /> Duplicate samples were submitted for general minerals analysis to determine water quality <br />„ parameters for the project area, Analytical results indicated that the shallow groundwater <br /> contains concentrations of total dissolved solids (TDS) ranging from 2,190 milligrams per liter <br />{ (mg/L) to 2,560 mg/L. In accordance with the Water Quality Control Plan for the Sacramento <br /> i River Basin and the San Joaquin River Basin (Basin Plan), groundwater having a TDS of less , <br /> than 3,000 mg/L is considered a potential source of drinking water. The State of California <br /> Department of Health Services Recommended Maximum Contaminant Level for TDS in <br /> drinking water is 500 mg/L. ' <br /> The Foster Well, currently being used at a nearby residence and identified within the project <br /> area was also sampled. This well is upgradient more than 100 feet beyond (southwest) the ' <br /> delineated area of crude oil affected soil and groundwater. The analytical result of the water <br /> sample was ND for petroleum hydrocarbon compounds and reported a TDS concentration of <br /> 2,400 mg/L. The results for analysis of water quality parameters for all of the samples ' <br /> collected at the Site that exceed respective screening levels include boron ranging from 3.7 to <br /> 6.8 mg/L, chloride between 562 and 688 mg/L, and sodium at concentrations of 549 mg/L to <br /> 674 mg/L. , <br /> Based on the previous reports and the November 2009 Report, SAIC concluded that: <br /> l The lateral extent of crude oil affected soil and groundwater has been defined by ND <br /> analytical results for crude oil/petroleum hydrocarbons and/or respective results which <br /> j did not exceed applicable environmental screening levels. ' <br /> The lateral and vertical extent of affected soil and groundwater has been defined in both ' <br /> areas and additional investigations are not needed. <br /> + Based on the results of testing for water quality parameters, the Site groundwater is not <br /> suitable for drinking water use; several components exceed State of California <br /> Department of Health Services Recommended Maximum Contaminant Levels for <br /> drinking water. ' <br />