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ChevronTexaco—Vernalis Pump Station,Vernalis,CA. Project No. 06-6102-00-6369-201 June 29,2004 Page 5 of 7 according to SJCPHS/SCDER requirements and advance contingency borings at the locations shown on Figure 2. Based on the analytical results from the Geomatrix Report of Soil and Groundwater Investigation, dated January 5,2004, SAIC is planning five contingency borings to define the lateral extent of affected soil and groundwater. Following completion of the soil borings,the open boreholes will be destroyed according to SJCPHS/SCDER requirements. Soil samples will be submitted to a California State-certified laboratory,Lancaster Laboratories (Lancaster)in Lancaster, Pennsylvania(ELAP#2501),under proper chain-of-custody protocol. Selected soil samples will be analyzed for BTEX by U.S. Environmental Protection Agency(EPA)Method 8021B, TPHc by EPA Method 8015 modified, and PAHs by EPA Method 8270C Select Ion Monitoring(SIM). SAIC will also obtain grab groundwater samples from select soil borings and submit them to Lancaster under proper chain-of-custody protocol for the following chemical analyses: BTEX by EPA Method 826013; TPHg and TPHd by EPA Method 8015 modified; TPHd by EPA Method 8015 modified with silica-gel cleanup; and PAHs by EPA Method 8270C SIM. TASK 4—WELL INSTALLATION,QUARTERLY GROUNDWATER MONITORING AND SAMPLING SAIC is recommending the installation of five groundwater monitoring wells(MW-5 through MW-9)to be incorporated into a quarterly monitoring and sampling program with the four existing groundwater monitoring wells (MW-1 through MW-4)located northwest of the former pump house. SAIC is proposing additional wells and initiating a monitoring and sampling program of 4 quarters to establish a chemical data base to verify that residual contamination beneath the site is stable and confined to the proposed investigation limits to be determined. In addition,the installation and sampling of groundwater monitoring wells will provide a higher quality groundwater sample that will enable the analytical laboratory to achieve the needed detection limit required by the Department of Toxic Substances(DTSC) for use in a Human Health Screening Evaluation(HHSE). If groundwater sampling results are consistent and the residual petroleum beneath the site is stable and confined throughout one hydrological cycle, SAIC will recommend additional sampling is not warranted and request the site be considered for"No Further Action"(NFA). It is understood that a NFA status will only be granted by the RWQCB following an evaluation of the HHSE by DTSC. Task 4.2—Installation of Groundwater Monitoring Wells Four groundwater monitoring wells are being proposed northeast of previous borings SB-19 and SB-20, and northeast of proposed borings SB-27 and SB-28. An additional well is proposed west(up gradient) of the former western Aboveground Storage Tank(AST)to be an up-gradient measuring point for depth to groundwater and to define up-gradient chemical concentrations. During advancement of soil borings east-northeast(down gradient)of the former pump station, SAIC will evaluate each borehole as described in Task 3. If a significant interval of affected soil is observed in the primary borings, SAIC will drill a contingency boring further down gradient. SAIC intends to construct monitoring wells in areas where affected soil is not observed. Monitoring well locations are shown on Figure 2. The proposed groundwater monitoring wells will be constructed of 2-inch diameter, flush-threaded, Schedule 40 polyvinyl chloride (PVC)well casing with 20 feet of 0.010-inch machine slotted well screen backfilled with Monterey 2/12 sand. The well seal will be constructed with a bentonite transition seal and neat cement containing approximately 5 percent bentonite to surface grade. The well head will be completed above ground and protected with steel bollards. Well construction details are presented on Figure 3. After installation,the new monitoring well locations will be surveyed by a licensed surveyor for horizontal locations and top of casing vertical elevations. The survey of the newly installed wells will incorporate existing site wells. Following well construction, SAIC will develop and sample the wells in