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Draft OU-1 ROD Memorandum -6- 4 June 1993 <br /> DDRW, Tracy <br /> Section 5.2.12 (Page 5-4). The Draft ROD states that TCE and PCE have migrated at <br /> different rates of 80 feet per year (ft/yr) and 40 ft/yr, respectively. This <br /> statement implies that TCE moves more rapidly in ground water than PCE, which is not <br /> accurate. Both contaminants if dissolved in ground water will migrate at the same <br /> rate as the ground water flow and magnitude. The difference in the extent of the <br /> plumes are due in part to the location, time and quantity of the release from the <br /> source area. This statement should be revised to reflect the differences in the <br /> extent of the plumes versus the average velocity of ground water flow at the site. <br /> Section 5.3.1 (Page 5-5). The statement regarding other potential chemicals of <br /> concern in ground water including boron, nitrate, dieldrin, CCL4, chloroform and <br /> metals as having off-site sources or naturally occurring should be revised to state <br /> that the sources may be on-site as well as off-site. The determination of whether <br /> any of these contaminants have resulted from on-site waste disposal activities will <br /> be addressed in the site-wide RI, and any necessary groundwater remediation will be <br /> addressed in the site-wide ROD. <br /> Section 6.2.4.7.2 (Page 6-9) . The Draft ROD states that CCL4 ground water <br /> contamination is likely due to an off-site source. This statement should be revised <br /> to that CCL4 ground water contamination may have an off-site source. DDRW, Tracy <br /> will remain a potentially responsible party for the CCL4 ground water contamination <br /> until the site-wide RI is completed. <br /> CKW:cw <br />