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is Geomatrix <br /> background conditions in the area of the stockpiled material. The GMP was approved by the <br /> RWQCB on January 31, 2002. <br /> 2.1 PREVIOUS INVESTIGATIONS <br /> An investigation of soil in the vicinity of the stockpiles at the Facilities was conducted during <br /> the installation of the groundwater monitoring wells (URS, May 2002) and as part of the <br /> vadose zone soil investigation (URS, December 2002). Details of these soil investigations <br /> were summarized by URS in the Feasibility Study and Remedial Options (FS/RO)Report <br /> (URS,December 2002) and the results are briefly discussed below. <br /> Three groundwater monitoring wells were installed around the perimeter of each stockpile <br /> (URS,May 2002). The groundwater monitoring well locations are shown on Figures 2 and 3. <br /> Soil samples were collected from depths of 1, 2.5, 5, and 10 feet below ground surface (bgs) <br /> and near the capillary fringe of the water table. These samples were analyzed for diesel-range <br /> petroleum hydrocarbons (TPHd), Cr, and Cr VI. Soil samples collected at 1 and 5 feet bgs <br /> were tested for extractable concentrations of TPHd, Cr, and Cr VI by Title 22 Waste Extraction <br /> Test Method using de-ionized water(DIWET) as the extraction media. A summary of the <br /> results and test methods is provided below: <br /> Concentration in Soil(mg/kg) TPHd Cr Cr VI <br /> (EPA Method (EPA Method 6010) (EPA Method <br /> 8015M) 7199) <br /> Lathrop < 1.0—5.8 2.8-19 <0.005—0.192 <br /> French Camp <1.0-51 2.4- 13 <0.005—0.010 <br /> Concentration of Soil Extracts(mg/1) TPHd Cr Cr VI <br /> DIWET Method (EPA Method (EPA Method 6010) (EPA Method <br /> 8015M) 7199) <br /> Lathrop <0.05—1.8 <0.01—0.01 <0.0005—0.013 <br /> French Camp <0.05 <0.01 <0.0005—0.0018 <br /> At Lathrop, THPd was detected at a concentration of 5.8 milligrams per kilogram (mg/kg) in <br /> one shallow soil sample collected from a depth of 5 feet bgs at boring LPW-3. Extractable <br /> diesel-range petroleum hydrocarbons were detected at a concentration of 1.8 milligrams per <br /> liter(mg/1) in one soil sample colleted from a depth of 1-foot bgs at boring LPW-3. In <br /> addition, the highest concentrations of total and extractable Cr and Cr VI were detected in the <br /> 1-foot soil sample collected from boring LPW-3. The extractable concentrations of these <br /> PAI 0626.000.O\Docs\M1.T Soil Work Plan.doc 2 <br />