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' INTERIM SOIL AND GROUNDWATER <br /> • CORRECTIVE ACTION SUMMARY REPORT <br /> 8940 W Walnut Grove Road, Thornton, CA <br /> (sample EXW 3/20/00), benzene was reduced from 1,900 ppb to 4 8 ppb, and MTBE was <br /> reduced from 3,500 ppb to 690 ppb Analytical results are presented in Table 6 Laboratory data <br /> ' sheets and chain of custody documentation are included in Appendix D <br /> ' 5.0 CONCLUSIONS <br /> Approximately 3,700 cubic yards of soil was excavated from the area immediately surrounding <br />' the former USTs The excavation proceeded to a depth of approximately 15 feet bgs where <br /> subjective analysis and field FID readings suggested the vertical extent of contamination had been <br />' reached Approximately 1,100 cubic yards of soil was classified as clean, and was utilized as <br /> backfill material Approximately 2,600 cubic yards of low to moderately impacted soil remains <br />' stockpiled on site Confirmation soil samples collected from the sidewalls and floor of the <br /> excavation confirmed that virtually all contaminated soil has been excavated <br /> Approximately 60,000 gallons of contaminated groundwater was pumped from the excavation, <br /> treated through ex-situ air-sparging to reduce contaminant concentrations, and subsequently <br /> 9 Y <br />' transported to the Sacramento County Regional Wastewater Treatment Plant for disposal under a <br /> temporary discharge permit Analytical results from groundwater samples collected on the first <br />' day of excavating and after interim remedial measures were completed indicated that petroleum <br /> hydrocarbon constituents were reduced by approximately 97 6-99 9%, except for MTBE, which <br />' was reduced by 80 3% <br />' 6.0 RECOMMENDATIONS <br /> In accordance with the October 19, 1999 Subsurface Investigation Summary Report prepared by <br /> Ground Zero, and pursuant to a directive by PHS/EHD dated February 16, 2000, Ground Zero <br /> recommends the installation of four groundwater monitoring wells to confirm the efficacy of interum <br /> corrective action measures and to evaluate c6rrent groundwater conditions beneath the site The <br /> locations of proposed monitoring wells are shown on Figure 7 The wells would be installed following <br /> accepted industry standards in accordance with Ground Zero's general field protocols(Appendix E) <br /> I <br /> G1DatalGROUNDZEIMANSER1Repom\soilexsum doc 7 <br /> I <br />