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former tank area. The lateral extent of groundwater impact appears to be defined to the west , and southwest based on the lack of PHCs in groundwater samples from borings B5-2 and B5- 3. However, the lateral and vertical extents of groundwater impact in areas north and east of the former tanks have not been defined. Field observations and analytical data for soils near the former dispenser area indicate that soils are not significantly impacted and that the vertical extent of PHCs in soils is no more than 5 to-LO feet bgs. However, the lateral and vertical extents of PHCs in groundwater in the vicinity of the dispenser were not determined in this initial investigation. According to Tri-Regional Board Staff Recommendations (Central Valley Regional Water Quality Control Board, 1991 - Recommendations for Preliminary Investigation and Evaluation of Underground Storage Tanks, Appendix A), when groundwater has been shown to be contaminated as a result of a tank leak, the site investigation is to proceed in phases. Following Tri-Regional recommendations, the next step recommended for Site 5 would be to -` develop a work plan to complete the site characterization near the former tank and dispenser + areas in order to prepare a Problem Assessment Report (PAR). A PAR describes the lateral and �! vertical extent of the problem, and proposes mitigative or remedial actions for a site. Further discussion related to the cost effectiveness, technical feasibility, and environmental appropriateness of potential corrective actions will be more constructive once the PAR has been completed.. A work plan designed to collect the information necessary to complete the PAR at Site 5 My include, but not be limited to, the following investigative procedures: 01 Soil-g sur gy-soil gas surveys have been successfully employed to outline the general extent and direction of subsurface petroleum hydrocarbon plumes in soil or groundwater, as an aid in directing the location of subsequent soil or groundwater,sampling, or in,the placement of monitoring wells. o DMI th-discrete soil and _or groundwater sampling - additional soil and groundwater sampling in areas peripheral to the former tank area will be necessary to define the lateral and vertical extent of contamination. o Monitoring well installation - Monitoring wells appear to be indicated for two reasons: (1) to establish the site-specific gradient direction or variations therein, and (2) to collect periodic groundwater samples to demonstrate either (a) stabilization or attenuation of PHCs in groundwater, or (b) the effectiveness of groundwater remediation should that be deemed necessary. Although data on groundwater direction and gradient are available from monitoring wells located on other sites within the Port complex (e.g., SPGC, 1998, and EMCON, 1998), these data show variable direction and gradient. Therefore, site-specific 8 %117UNVF1gS 5USTWV.Rff