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from three depth intervals at each boring The purpose of these activities <br /> was to verify that residual hydrocarbon concentrations, if present in site <br /> soils, would not pose a significant risk to human health and the <br /> ' environment The results of these additional characterization activities <br /> were presented in a report entitled Environmental Conditions Report- 1325 <br /> and 1515 West Weber Avenue - Stockton, California (ERM,July 1995, <br /> ' hereinafter, "Environmental Conditions Report") <br /> The data collected during this investigation verified the accuracy of the <br /> 1993 excavation confirmation sampling and supported the 1993 <br /> confirmation sampling results that indicated that soils exceeding the TPH <br />' cleanup goal had been excavated Furthermore, the data indicated that <br /> significant volumes of TPH-impacted soils did not appear to be present <br /> beneath the building at Former Tank Site #1 A figure summarizing the <br />' TPH concentrations detected in soils in the former Tank Site #1 area is <br /> included in Appendix B <br />' <br /> 26 MASS CALCULATIONS FOR SOIL TREATMENT <br /> Mass calculations were completed to evaluate the volume of soil treated at <br /> Site #1 by excavation and aeration Appendix C presents the details of the <br /> M mass calculations In summary, these calculations indicate that the mass <br /> of TPH and BTEX were reduced by 97 percent and 96 8 percent, <br /> respectively <br /> 27 GROUND WATER MONITORING AND REMEDIATION <br /> The ground water remedial alternative originally selected for Former <br />' Tank Site #1 involved extraction of a fixed volume of hydrocarbon- <br /> containing ground water from existing monitoring wells Ground water <br /> was extracted from monitoring wells MW-4 and MW-5 during three <br />' events December 1993/January 1994, May 1994, and September 1994 <br /> The ground water extracted during each event was pumped into Baker <br /> tanks for temporary storage and subsequently transported via vacuum <br /> trucks to the City of Stockton Publicly-Owned Treatment Works (POTW) <br /> for direct discharge In October 1996, oxygen regenerating compounds <br />' (ORC) were introduced to the monitoring system to enhance natural <br /> biodegradation processes <br />' Ground water samples were collected routinely from the five wells <br /> installed at Site #1 between April 1991 through July 1999 The results of <br /> these monitoring events indicate that the gradient varies, probably due to <br /> tidal water level fluctuations in the nearby Deep Water Channel <br />' ERM 11 CArLLLUS/299610-10/13/99 <br />