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Tracy Well Survey -6- 28 December 1995 <br /> RWQCB <br /> water at the site, carbon tetrachloride contamination may be migrating southwest across the APC <br /> site, and into the APC production wells. These production wells may be acting as a conduit for <br /> contaminant flow into the Middle Hydro-Stratigraphic Unit (middle horizon)within the Upper <br /> Tulare Formation(one production well is screened to 150 feet bgs). This carbon tetrachloride <br /> contamination is potentially migrating to the northeast with the natural ground water flow during <br /> periods when production well pumping is substantially decreased or pumps are shut off. The <br /> domestic supply well at the Rose property is screened over the interval from 85-105 feet bgs, <br /> (middle horizon). <br /> Chloroform contamination <br /> The data evaluated indicates that soil source areas for chloroform ground water contamination <br /> exist at both the All Pure Chemical Co. and the Triple E Produce sites. Based on the distribution <br /> of contaminant concentrations and local ground water gradients, separate source areas appear to <br /> be present which are resulting in different areas of ground water contamination. <br /> RECOMMENDATIONS <br /> An investigation is necessary to delineate the nature and extent of the CCI, ground water <br /> contamination which exists beneath the All Pure Chemical site and along a north-south path in the <br /> vicinity of South Banta Road. Potential affects of local pumping, including pumping rates of the <br /> on-site production wells, should be evaluated as part of a focused ground water investigation at <br /> the APC site. Over time, the affects of the DDRW Tracy ground water remediation on the CCI, <br /> ground water contamination should also be evaluated <br /> An investigation to delineate the nature and extent of chloroform ground water contamination at <br /> the APC site is warranted. The nature and extent of the chloroform contamination at the Triple E <br /> Produce site has not been completely defined. However, a bioremediation method to treat <br /> contaminated ground water extracted from MW-4A and MW-2 began in July of 1993. Because <br /> this method has had limited success, the Regional Board is a reviewing a proposal recently <br /> submitted by the Triple E site to expand these ground water extraction and treatment processes. <br /> This report prepared by: Karen Bessette !/ <br /> DDRW Tracy P sect Engineer <br /> Mark List <br /> Student Assistant <br />