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Feasibility Study/Corrective Action Pian 6 The Drake Property,26485 Thornton Road Thornton California November 26 1996 values expected from natural attenuation, as discussed above and in Section 5 0 Third, sod samples /] collected from borings B-1 through B-10 show that BTEX concentrations in soil around the site are declining l through natural attenuation, as discussed above And fourth, non-detectable benzene levels to all sod samples and all but one historic groundwater samples, do not warrant additional site assessment activities so REQUEST FOR "NO FURTHER ACTION" "No Further Action"is the best option for this site because current site conditions conform to "low-risk"site classification criteria as specified by the CSWRCB (CSWRCB, 1995), and CRWQCB-CVR (CRWQCB- CVR, 1996) These criteria consider the economic cost versus benefit of conducting further environmental remedial activities on a site already meeting "low-risk" conditions Discussions concerning the site have been conducted with the CSWRCB in which the CSWRCB has stated that no additional assessment or remediation activities at the site will be approved for reimbursement (pers comm , 1996) The site meets the qualifying criteria for"No Further Action"status, as follows r) Contaminants in the vadose zone must not reverse or threaten to reverse the mass reduction rate of groundwater pollutants discussed in lv) below The contaminant source has been mitigated with UST removal and overexcavation of the UST pit and associated piping (Section 2 1) The low BTEX and TPH-G concentrations in soil and groundwater samples collected from 1993 and 1995 site assessment activities (Tables 1-3) show that the majority of hydrocarbons have been removed from the site The total estimated residual hydrocarbon volume at the site is less than five gallons (Appendix A) n) Separate phase has been removed from the site to the extent practicable No separate phase currently exists on site The source has been removed via UST removal and excavation activities (Section 2 1) in) No existing water supply wells, deeper aquifers, surface waters or other receptors are threatened by pollutants remaining in the aquifer A survey of Department of Water Resources records for pumping wells located within a 2,000-foot distance from the site indicated 2 wells to be within approximately 250 feet of the site, and an additional 6 wells within approximately 2,000 feet Gable 4) According to recent guidelines set forth by the CSWRCB (CSWRCB, 1995), an -the CWQCB- VR (CWQCB-CVR, 1996), residual hydrocarbons on site pose only a "low risk"to the{existing water ply The source has been removed, and BTEX concentrations in groundwater are of California Maximum Contaminant Concentrations 0191 FEA RPT(Mise 15) .6::nL 1 ' FLUOR DANIEL GTI