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Science Applications International Corporation ® An Employee-Owned Company June 28, 2005 HPP-BTR MP 9204.4 Vernalis Pump Station Correspondence—R W QC B Mr. M. Scott Mansholt Chevron Environmental Management Company 6001 Bollinger Canyon Road Room K2066 San Ramon, CA 94583 Subject: Soil and Groundwater Evaluation Draft Analytical Results from May 2005 Investigation Vernalis Pump Station 35500 Welty Road Vernalis, California Dear Mr. Mansholt, Based on the soil and groundwater sampling results collected during the May 2005 site investigation of the above-referenced site, SAIC has prepared this draft evaluation of subsurface conditions beneath the former Vernalis Pump Station and adjacent properties. During May 16 through 24,2005, SAIC observed Gregg Drilling(C57#485165)advance six soil borings(SB-22 through SB-36)and three well borings(MW-5 through MW-7)at the site. The soil and well borings were advanced to various depths between 40 and 71.5 feet below ground surface(bgs). Soils encountered during the investigation ranged from clays(CL)to poorly graded sands(SP) and minor gravels(GP)with fines. During the May 2005 investigation, SAIC collected soil samples from select depths that coincided with sampling depths from previous soil borings. Grab groundwater samples were also collected from select borings at first-encountered groundwater. Draft analytical results from soil and grab groundwater samples collected during the May 2005 investigations are summarized in Table 1 through Table 4. Draft soil and grab groundwater concentration maps are presented on Figures 1 and 2. Analytical results are discussed below. ANALYTICAL RESULTS Eighteen soil samples were collected from the seven borings completed. Benzene,toluene, ethylbenzene, or total xylenes(BTEX)were not detected in any of the 18 soil samples analyzed. Total petroleum hydrocarbons quantified as crude oil (TPHc)were not detected in 16 of the 18 soil samples analyzed. TPHc concentrations were detected in two samples collected from soil borings SB-22 and SB-23 at concentrations of 330 milligrams per kilogram (mg/kg)and 380 mg/kg, respectively. Both soil samples containing TPHc detections were collected at a depth of 1 foot bgs. All samples collected below 1 foot bgs did not contain detectable TPHc or BTEX compounds. Several polynuclear aromatic hydrocarbons(PAHs)were detected in 5 of the 18 soil samples analyzed at concentrations ranging between 0.0003 to 0.007 mg/kg. Based on the soil chemical analytical results, it appears affected soil north-northwest, north-northeast, south- southwest, and south-southeast of the former boiler house and pump house has been laterally delineated.