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Mr. M. Scott Mansholt—CEMC June 28,2005 Soil and Groundwater Evaluation, Vernalis Pump Station Page 2 of 2 Five grab groundwater samples were collected from select borings during the May 2005 investigation. BTEX compounds were not detected in any of the grab groundwater samples except for the sample collected from SB-22,which contained detectable benzene and toluene at concentrations of 0.5 micrograms per liter(gg/L)and 2.0 gg/L, respectively. TPH quantified as diesel(TPHd)were detected in three of the five grab groundwater samples analyzed ranging in concentrations between 560 gg/L(SB-23)and 780 gg/L(SB-22). Following a silica-gel cleanup procedure,TPHd were detected in grab groundwater sample SB-25 at a concentration of 240 gg/L. Several PAHs were detected in grab groundwater samples SB-25 and SB-36 at concentrations ranging from 0.01 gg/L to 0.9 gg/L. Based on the grab groundwater chemical analytical results, it appears that affected groundwater is delineated west-northwest of the former pump house and boiler house. However, groundwater north-northeast and southeast of the former pump house and boiler house appears to be affected by dissolved-petroleum constituents. RECOMMENDATIONS Grab groundwater samples collected during the May 2005 soil and groundwater investigation were collected using a peristaltic pump and tubing drawn through a 1 inch-diameter polyvinyl chloride temporary well casing. The samples collected were noted as turbid with a high sediment load, indicative of grab groundwater samples collected from an open Geoprobe®borehole. Based on previous grab groundwater samples collected at various HPP sites, detections of TPHd are likely to be a result of polar organics derived from intrinsic biodegradation of residual petroleum beneath the subject site. With the addition of the newly installed groundwater monitoring wells, SAIC is recommending four quarters of groundwater sampling be conducted to evaluate groundwater quality. However, to fully characterize soil and groundwater at the subject site, SAIC recommends the proposed borings SB-26 through SB-29 located east-southeast of the former boiler house and pump house be advanced adjacent to Highway 33. If residual petroleum is encountered, then proposed monitoring wells MW-8 and MW-9 should be considered for installation and incorporated into the quarterly monitoring program. Since access to the property has not been granted by the property owner, SAIC recommends the RWQCB attempt to discuss access with the property owner in an effort to complete the proposed scope of work. If you have any questions please call me at(916)979-3741. Sincerely, SCIENCE APPLICATIONS INTERNATIONAL CORPORATION Todd Del Frate, P.G. Senior Geologist/Project Manager Enclosures: Draft Figure 3: Soil Sample Concentration Map Draft Figure 4: Grab Groundwater Sample Concentration Map Draft Table 1: Soil Sample Analytical Results(TPHc and BTEX) Draft Table 2: Soil Sample Analytical Results(PAHs) Draft Table 3: Grab Groundwater Sample Analytical Results(TPHd/BTEX) Draft Table 4: Grab Groundwater Sample Analytical Results(PAHs)