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Mr. Maurice Benson <br /> February 11, 2010 <br /> Page 3 <br /> contradicts information provided in Section 3 of the report. Specifically, Section 3 <br /> of the report indicates that results from the new off-site monitoring well (MW) <br /> cluster MW537 and 2007/2008 Hydropunch® data necessitated a revision of the <br /> 25 micrograms per liter (ug/L) and 100 pg/L trichloroethene (TCE) isopleths due <br /> to the larger areal extent of the off-site TCE plume. Off-site MW537C showed a <br /> TCE concentration of 412 pg/L in 3Q09, the highest contaminant concentration <br /> detected in a DDJC-Sharpe groundwater well. This information combined with <br /> the off-site Hydropunch® analytical data showing TCE concentrations above 25 <br /> pg/L another 1,000 feet farther north than previously identified indicates the likely <br /> migration of the groundwater plumes while the treatment and extraction systems <br /> were operating. <br /> In order for monitored natural attenuation to be considered as a viable <br /> component of the pump and treat remedy for the DDJC-Sharpe Record of <br /> Decision, specific criteria must be met as provided in the United States Air Force <br /> MNA Guidance, dated 1995. The first metric that must be met as part of <br /> monitored natural attenuation is the evidence that the plume is not migrating <br /> under normal conditions (i.e. no pumping conditions). Currently at DDJC-Sharpe <br /> there are 15 operating extraction wells in optimization configurations to extract <br /> and treat contaminated groundwater, but also to create a hydraulic influence to <br /> help mitigate and ideally capture contaminant plumes migration due to off-site <br /> and normal regional hydraulic influences. The fact that operating extraction wells <br /> are responsible for creating a hydraulic influence to counter the regional <br /> groundwater flow is one aspect demonstrating why MNA is not a viable remedy <br /> component at DDJC-Sharpe. The report should clearly identify the criteria <br /> necessary for the demonstration of MNA and also be concise in identifying <br /> whether the DDJC-Sharpe characteristics or data support MNA. <br /> 4.) Page 4-5, section 4.3.2: See comment#3. <br /> 5.) Page 4-9, section 4.3.3.5: In 2005 during meeting discussions, DTSC's Project <br /> Manager (PM) and the Water Board's previous PM, Mr. Marcus Pierce, notified <br /> DESJC of the downward vertical gradients caused by the operation of <br /> DDJC-Sharpe PW038, PW039, and PW040. The State noted that the bases <br /> operating potable wells were pulling the North Balloon TCE plume from the upper <br /> hydrologic zone eastward and downward into the middle and lower zones <br /> supported by the hydraulic responses and analytical results from the above- <br /> mentioned potable wells including the MW447 and MW499 series wells. DESJC <br /> has known for several years of the downward vertical gradients caused by its <br /> operating PWs yet has not proposed a viable solution other than stating that <br /> "...the hydraulic influence of the water supply wells on vertical plume migration in <br /> the North Balloon is ongoing." <br />