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1 <br /> ' If groundwater degradation should occur in the future there is no reason to believe that the levels <br /> 1 would be present at a magnitude greater than historical levels The likelihood of groundwater <br /> contamination, migrating off-site should the degradation occur, is minimal due to the size of the <br /> I <br /> Property The northern property boundary, which is in the general downgradient direction, is <br /> ' approximately 1300 feet from the former tank location <br /> 1 5.0 SPECIFIC INFORMATION FOR CLOSURE REQUEST <br /> .11 Introduction <br /> 1 This section provides information specifically required for closure review as per the October 7, <br /> 1993 Addendum to Appendix A of the Tri-Regional Recommendations <br /> ' 5.2 Rationale for Closure <br /> Based on the results of the confirmation boring sampling, it appears that residual contamination in <br /> 1 the soil to 9 feet bgs is limited to a small area immediately adjacent to the light pole on-site, and <br /> limited to small areas along the former east and west sidewalls of the former overexcavation An <br /> estimated 800 cubic yards of petroleum hydrocarbon contaminated soil was removed during tank <br /> pit overexcavation The estimated mass of contaminants left in place due to physical constraints <br />' <br /> in soil to 9 feet bgs is 48 pounds, which is approximately 10 7% of the estimated total mass of <br /> contaminants in the soil on-site (Table 5 and Appendix VI) This estimated mass is based on the <br /> results of laboratory analyses conducted on the excavation confirmation samples These samples <br /> 1 were collected in July 1990 Thus, the residual mass of TPHd in the soil may be less than 48 <br /> pounds due to natural degradation of the TPHd It appears that the residual soil contamination is <br /> 1 not affecting the groundwater based upon the lack of TPHd detected in groundwater on-site in <br /> the last six quarters of groundwater monitoring Thus, no apparent threat to groundwater exists <br /> 1 5.3 Site Specific Information Summary <br /> rY <br /> 1 o Five groundwater supply wells are known to exist within 2000 feet of the site, based upon <br />' information provided by the Department of Water Resource (RESNA correspondence, <br /> 1994) Locations of the wells are shown on Figure 2 in Appendix V <br /> • Site maps, to scale, of the area impacted showing locations of the former UST, nearby <br /> surface waters, buildings, streets and known utilities are presented on Figures 1 and 2 <br /> w 1967311repoiuNC1osure dm 7 <br /> • <br /> 1 <br /> SMTH <br />