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' Assessment Report which is summarized in Appendix A for findings and data. Subsequently, the California Water Quality Control Board (CWQCB) , Central Valley Region, requested that an investigation be conducted to assess the effects of the leaking UST on groundwater. 4. SITE REMEDIATION ' 4. 1 Contaminant Information In March 1988 two 10, 000 gallon UST' s were removed from the site. Analytical results of soil samples beneath the UST' s indicated concentrations of key petroleum product constituents. Therefore, a preliminary soils investigation was conducted by Kleinfelder on March 3 and 4, 1988. At this time water samples only were taken at the request of Mr. Jaime Favila, the PHS-EHD representative, due to the shallow groundwater. Two samples were taken from the east side of the excavation, the first at 7 feet and the second at 7. 5 feet. The results of the water sample analysis revealed concentrations of benzene (#I- 2,200 ug/1 and #2-10,000 ug/1) , toluene (#1-71 ug/1 and #2-32,000 ug/1) , Ethyl benzene (#1-220 ug/1 and #2-11,000 ug/1), and total volatile hydrocarbons (TPH) of #1-59 mg/1 and #2-86 mg/1. Based on these findings, the soil underlying the former UST location was excavated and aerated on-site. The excavation was 40 feet in length, 40 feet in width, and 12 feet in depth. New tanks were installed in March 1988. The plan view of the plume is shown in Figure 1. The cross-sectioned view of the plume is shown in Figure 2. The estimated volume of contaminated soil and aquifer is 2000 cubic yards, and contaminated aquifer is 625. �I PLUME VERIFICATION TOTAL. . . . . . . . . . . . . . . . . . 85 x 80 x 8/27 = 2014 CY Figure 1 displays the horizontal extent of petroleum product migration; ' and Figure 2 displays the cross-sectional (vertical) migration. Soil borings BH1 through BH7 were performed to identify the geometry (both horizontal and vertical ) of the hydrocarbon plume. Soil samples from the borings were collected at 4 feet and 7 feet. Table 2 shows the soil sample analytical results for each sample taken and its corresponding depth. The vertical extent of petroleum products migration has not been established due to the heavy rains. The combination of soil borings and analytical laboratory testing are used to justify-t-1 the geometry of the petroleum hydrocarbon migration as shown in Figure 1. 4. 2 REMEDIATION METHOD The augmented in situ subsurface bioremediation process that will be used by Pacific Rim Environmental has been successfully implemented on over seventy- five sites in eighteen states. Appendix A details four case histories. Case ' History 82490 has been specifically outlined and is included in its entirety. This site was tested for petroleum hydrocarbons and the closure was verified approximately one (1) year after the site was completed. A copy of the manufacturer' s brochure detailing technology and the proprietary non-pathogenic biocultures has been included in Appendix A, referred to as the MSDS sheet and 4