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�- 5.0 SITE CLOSURE CRITERIA <br /> This request for case closure follows the Tri-Regional Board Staff Recommendations for <br /> Preliminary Investigation and Evaluation of Underground Tank Sites, Appendix A. A checklist of <br /> closure criteria is included as Appendix G. <br /> 5.1 Sources <br /> Subsurface investigations at the site have documented that petroleum hydrocarbon and fuel <br /> oxygenate impacts to soil and groundwater are primarily limited to the general vicinity of the <br /> former USTs, located as shown on Figure 2. No significant impacts to soil or groundwater have <br /> been documented outside of the former UST excavation area. <br /> No free product has been identified at the site. The removal of the UST and related piping, and <br /> the related excavation of the UST location, has eliminated the main source at the site. <br /> .. The total estimated mass of petroleum hydrocarbons remaining in soil at the site, based on a <br /> circular impacted area with a radius of 20 feet and the analytical results of soil boring CPT-1A <br /> are as follows: <br /> -TPH-as-gasoline 520 pounds <br /> Benzene 0 pounds <br /> The total estimated mass of MTBE in groundwater at the site, based on fourth quarter 2005 <br /> groundwater monitoring data is 0.13 pounds. This represents approximately 94% of the TPH- <br /> as-gasoline and 100% of the benzene present prior to remediation by SVE. <br /> 5.2 Site Characterization <br /> The site characterization details are discussed in the Site Conceptual Model (Section 3.0). The <br /> soil boring, monitoring well and CPT locations are shown on Figures 2 and 3, the cumulative soil <br /> sample analytical results are summarized in Table 1, the cumulative groundwater analytical <br /> results from the monitoring wells are summarized in Table 3, the well construction details and <br /> cumulative groundwater monitoring data are summarized in Table 4. The CPT confirmation soil <br /> sample analytical results are summarized in Table 5 and the CPT deep groundwater analytical <br /> results are summarized in Table 6. The following is a brief list of site characterization tasks <br /> completed at the site: <br /> 21 <br />