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1� Mmadwell&Rollo <br /> 1 4.7 Groundwater Extraction, Treatment and Disposal <br /> 1 Approximately 40,000 gallons of groundwater were pumped from the excavation and stored in <br /> 20,000 gallons Baker Tanks prior to analysis. The analytical results indicated that the <br /> 1 groundwater exceeded the discharge requirements of the City of Stockton Municipal Utilities <br /> Department(SMUD). Therefore, the groundwater was filtered through carbon vessels and <br /> 1 re-sampled. Results of the second groundwater analyses met the SMUD requirements. <br /> Laboratory analytical reports for the groundwater samples are included in Appendix B. SMUD <br /> 1 accepted the groundwater for discharge in a 25 May 2004permit that is included in Appendix_D....r- <br /> 1 5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> 1 Site remediation, confirmation, and soil disposal activities were conducted at the site between 24 <br /> April and 11 May 2004 according to the 2004 Workplan. After remedial work was completed, <br /> the excavation was backfilled to previous grade. <br /> 1 All of the soil excavated from 10 to approximately 22-foot bgs (5-feet below the groundwater <br /> table) contained significant TPHg concentrations. The excavation soil sample(16-exc-23) <br /> 1 collected at 23 feet bgs contained significant TPHg concentrations, but previous sampling at <br /> 24.5 feet bgs in 16B-6b, located adjacent to 16-EXC-23, did not contain TPHg. On the basis of <br /> 1 this data, it appears that the majority of the contaminated soil from below the former UST has <br /> been removed. <br /> 1 Approximately 40,000 gallons of contaminated groundwater was removed from the excavation. <br /> 1 Analytical results from the confirmation groundwater sample indicate that the most contaminated <br /> groundwater at the site has been removed. Since groundwater analyses began at monitoring well <br /> MW-3 installed in the excavation area in 1996, concentrations of TPHg have not shown a <br /> significant change, averaging approximately 180,000 µg/L; in spite of several years of various <br /> 1 in-situ remediation technologies (air sparging, vapor extraction, and ozone sparging) being <br /> • operating at the Site. The TPHg concentration in the excavation groundwater sample was 4 to 5 <br /> times lower(43,000 µg/L)than in recent samples from borings 16B-6 andl6B-8, located in the <br /> 1 25971021.DJS 8 18 November 2004 <br />