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1 <br /> I6.0 DISCUSSION AND CONCLUSIONS <br /> 6.1 Comparison of Data to ESLs and PRGs <br /> ' The soil and groundwater data were compared to the San Francisco RWQCB environmental <br /> screening levels (ESLs) and the US EPA preliminary remediation goals (PRGs) The <br /> groundwater ESLs apply for sites where groundwater is a current or potential drinking water <br /> resource and the PRGs are for tap water According to the SFRWQCB, the presence of a <br /> chemical at concentrations below the corresponding ESL can be assumed to pose no significant <br /> long-term(chronic) threat to human health and the environment (SFRWQCB, 2003) However, <br /> these criteria are used in this report to provide baseline levels and to identify areas of potential <br /> concern but are not intended to provide an evaluation of risk <br /> ' No areas of concern appear to be present onsite based on the shallow soil sample results The <br /> ESLs and PRGs for soil at both residential and commercial/industrial land use sites are shown on <br /> Table 3 The TPH compounds detected in the shallow soil at the 541 Site did not exceed <br /> ' residential or commercial/industrial ESLs There are no residential or industrial PRGs <br /> established for TPH compounds MTBE and BTEX were below the residential or <br /> ' commercial/industrial ESLs and PRGs The deeper soil samples collected below the <br /> groundwater exceeded the ESLs for the TPH compounds and a few of the samples exceeded the <br /> ESLs and PRGs for MTBE and BTEX compounds (Table 3) It is likely that the soil sample <br /> results reflect the effect of groundwater contamination <br /> 1 The majority of TPH compounds detected in the shallow and deeper groundwater exceeded the <br /> ESLs of 100 ppb The ESLs and PRGs are shown on Table 4 As shown on Figures 8, 9, and <br /> 10, a broad area is underlain by groundwater containing TPH concentrations greater than 100 <br /> ppb with the highest concentrations west and southwest of the 541 Site There are no PRGs <br /> established for TPH compounds Most of the groundwater samples with detectable <br /> ' concentrations of MTBE and BTEX compounds exceeded the ESLs and PRGs <br /> • <br /> Field Investigation Report 16 8 December 2403 <br /> TREADWELL&ROLLO,INC <br />