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Analytical results are included in Table 7 Soil samples were not collected during the installation of wells MW-1R and MW-5R in November 1995 or well MW-5R2 in August 1996 4.2 Groundwater Conditions ' Shallow groundwater beneath the site has varied from 17 feet below grade to 29 feet below grade Historically, groundwater elevation data has suggested an irregular groundwater surface beneath the site, possibly due to the heterogeneous nature of the soils and/or the varying well depths The groundwater gradient generally flows to the south-southeast with a gradient of 0 005 f}/ft, or approximately 26 4 ft/mile The groundwater gradient measured on December 6, 1996 is depicted on Figure 5 Results from the most recent groundwater sampling event indicate that TPHg and BTEX are below method detection limits in wells MW-1R through MW-6 Wells MW-3 through MW-6 contain low to moderate levels of TPHd, however, the chromatogram pattern indicates the compound is an unidentified hydrocarbon in the diesel range Since the excavation activities in September and October 1995, detectable concentrations of HVOCs and BTEX have been below the MCLs Historical groundwater data is summarized in Tables 4, 5, and 6 5.0 SPECIFIC INFORMATION FOR CLOSURE REQUEST 5.1 Introduction This section provides information specifically required for closure review as per the October 7, 1993 Addendum to Appendix A of the Tn-Regional Recommendations 5.2 Rationale for Closure tThe impacted soil, the source of the groundwater contamination, was excavated and remediated on site in October 1995 and the site was subsequently repaved Based on the analytical results of the confirmation soil samples collected during the excavation in October t1995, it appears that the majority of impacted soil has been removed and remediated In addition, approximately 1,750 gallons of contaminated groundwater was extracted, treated, and disposed of in April 1990 and approximately 400,000 gallons of groundwater was extracted from the open excavation and disposed of into the City of Stockton sewer system in October 1995 The excavation of the majonty of impacted soil and the removal of over 400,000 gallons of impacted groundwater has resulted in decreasing concentrations of TPHg, BTEX, and HVOCs in groundwater to nondetectable levels Concentrations of TPHd in groundwater have decreased to moderate to nondetectable levels The remaining impacted soil ' is not expected to have a significant impact on groundwater because the site is paved The impacted soil and TPHd in groundwater are expected to naturally biodegrade to nondetectable levels over time and do not pose an immediate threat to human health or the environment w 1943311dlosure doc 6 SMTH l