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VA' Mr. Nathan Esformes -2- 15 May 1996 known. In addition, pumping from domestic wells, the Maurland Manor well, and Fair Oaks Wells 1 and 2 to the north of the extraction well will likely reduce the actual capture zone of the extraction well. It is necessary to determine the extent of the chloroform contamination to determine if residents are being exposed to elevated levels of chloroform and if the extraction system is capturing all of the contamination. Sustained decreases in chloroform in MW-7 will not necessarily be an indication that pumping is effective at containing the plume, since the plume may extend beyond the predicted or actual capture zone. Other Major Potential Sources The data available to date do not support the claim that All Pure Chemical (All Pure), Tracy Defense Depot (TDD), or the Georgia Pacific Chemical Packaging facility (Georgia Pacific) is a source of chloroform detected in the residential area northwest of Triple E. The All Pure facility is two miles northeast of Triple E. All Pure's monitoring well MW-4 and two supply wells have never had detectable chloroform. These wells are All Pure's closest wells to Triple E and thus separate All Pure's chloroform plume from the Triple E chloroform plume. The distribution of chloroform at the TDD has been very sporadic with the highest concentration at only 5.9,ug/l. There is no pond in the southern portion of TDD, nor has any chloroform ever been detected south of an east-west line through the intersection of the Western Pacific and Southern Pacific Rail Lines. Ground water flow directions in each of the four water-bearing zones identified by TDD have consistently been to the north-northeast . Georgia Pacific is northwest of Triple E and the residential area downgradient of Triple E. Ground water flow at Georgia Pacific has been consistently to the northwest, thus the chloroform plume at Georgia Pacific would not influence the chloroform plume originating from Triple E. As discussed in my 28 November 1995 letter, the amount of chloroform discharged from the swimming pools north of Triple E would not increase chloroform concentrations in ground water significantly, and there is no reason to suspect chlorinated compounds are discharged to septic systems in amounts that would result in significant concentrations of chloroform in ground water. Other Sources - Swimming Pools Triple E has stated that elevated chloroform may be detected in domestic wells due to domestic wells being sited close to swimming pools and back flush discharge areas. This is all the more reason to install monitoring wells to track the chloroform plume, rather than relying on domestic wells. This is what we have requested of Triple E, but due to your objections, we agreed initially to allow sampling of domestic wells to evaluate the need for additional monitoring wells. If Triple E refuses to sample the domestic wells, then we may require the installation of monitoring wells right away.