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First Quarter 1999 Post-Remediation Monitoring and Sampling Report/Requesi for Closure 3 The Southland Corporation,Store#20304,455 Grant Line Road,Tracy,CA April 15 1999 The highest TPH-G concentration was detected in groundwater from monitoring well MW-16 at 470 micrograms per liter(ug/L)while the highest benzene concentration was found in well MW-1 at 14 8 pg/L (Figure 3) MTBE was not detected in any of the wells sampled Historically, dissolved hydrocarbon concentrations in upgradtent and downgradient wells have been non-detectable Since the April 1998 ' excavation, dissolved hydrocarbon concentrations in the source area region have dropped approximately 96% (based on TPH-G concentration data taken from MW-16)while in peripheral wells they remain non- detectable Analytical results from the groundwater samples collected on March 17, 1999 are presented in Table 1, and historical analytical results are summarized in Table 1A The laboratory analytical reports and the chain-of-custody records for this sampling event are Included in Attachment 4 Closure Abstract Based oil 1) the removal of the hydrocarbon source from the site(LSTs and associated piping removed Marc 9 . _end residual hydrocarbon source area excavated April 1998), 2) the low to moderate residual hydrocarbon concentrations remaining in the groundwater at the site which are expected to decline over time, 3) source area concentration declines of up to 96%since completion of remediation, 4) the naturally occurring biodegradation of the dissolved hydrocarbon plume which is expected to continue, 5) data indicating that the dissolved hydrocarbons plume is stable and is not a threat to any nearby water producing wells, and 6) the absence of MTBE in the samples collected from existing site monitoring wells, the IT Corporation, on behalf of the Southland Corporation, requests that the site be classified as low risk under the State Water Resources Control Board policies and that no further action be required at the site 1 1 1 1 I 1 1 20304g199 RPT