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Mr. Dan Silva and Ms. Tina Mayhew 15 September 2009 <br /> West Clay Properties Page 2 of 4 <br /> 639 West Clay Street, Stockton, California 95206 <br /> groundwater to applicable cleanup goals in a timely manner and hasten site closure, saving time <br /> and money. <br /> Regarding feasible technologies to remediate impacted groundwater, in your letter AGE noted <br /> that insitu air sparging had not been field-tested, and concluded that previous field testing had <br /> demonstrated groundwater extraction (GWE) to not be feasible for the site and that ozone <br /> injection was cost effective; additionally, AGE recommended expansion of the ozone injection <br /> system to address other portions of the dissolved plumes. The EHD is not sure that ozone has <br /> been demonstrated as being effective for your site, noting that contaminant concentrations had <br /> started a significant decline prior to initiation of continuous ozone injection; in fact several wells <br /> in the area injected by ozone had achieved non-detect concentrations before ozone injection <br /> began, as demonstrated in the following chart: <br /> Ozone Remediation Area at 639 W.Clay Street <br /> 100000 <br /> ea <br /> 1000011 <br /> �c <br /> 10r <br /> a G <br /> a <br /> a \ce <br /> c 1oc� <br /> 1000 <br /> ■ O <br /> c <br /> -�-MW9 TPHg <br /> --W-MW 10 TPHg <br /> c <br /> V • • • -ter EW 1 TPHg <br /> -w-MW 12B MTBE <br /> c 100 • <br /> • <br /> c <br /> E • <br /> m <br /> c <br /> 0 <br /> U <br /> 10 <br /> 1 <br /> 'bF ISP <br /> 14T 14", <br /> Monitoring Events Conducted Between October 1999 and March 2009 <br /> Most related data points not connected by lines are separated by `non-detect' results, which <br /> cannot be plotted on a semi-log graph; a few may be missing data points. The enlarged data <br /> point labeled `Ozone Injection Initiated' marks the first monitoring event result obtained following <br /> initiation of ozone injection the previous month, November 2006; data to the right of the <br /> enlarged point was collected during the period of ozone injection system operation. The graph <br /> clearly shows that total petroleum hydrocarbons quantified as gasoline (TPHg) in monitoring <br /> well MW-10 had declined to undetectable concentrations or to greatly reduced concentrations <br /> by late 2003; methyl tert-butyl ether (MTBE) in MW-12B also declined sharply in late 2003, <br /> becoming undetectable by late 2005. Overall, the erratic hits of TPHg in MW-9 appear to be <br /> unaffected by the ozone injection. The concentration declines in MW-10 and MW-12B occurred <br /> Comment Letter 0909 <br />