SITE INFORMATION AND CORRESPONDENCE FILE 1

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CLEARWATER JUI- 1 1 1995 G R o u P, I N C. ENVIRONMENTAL HEALTH PERMIT/SERVICES Page 4, paragraph 2 - "PHS/EHD questions the necessity to modify the proposed feasibility testing..." The basis for the recommended modifications to the approved pilot testing program have been presented in this letter, and in previously transmitted submittals. If the PHS/EHD does not concur with the basis for the recommendations or the need for test modification, the test will be completed as proposed in the approved project workplan. It should be noted that information provided during the documented pre-test field evaluations suggests that the completion of testing in the manner originally proposed may not provide adequate long-term remedial design data. Conclusions and Recommendations Information presented in this letter and previously submitted reports and transmittals indicates the following: • It remains apparent that the ultimate long term remedial approach may involve a combination of groundwater and soil vapor extraction, with wells designed for the simultaneous extraction of these media utilized as extraction points. • Low oxygen concentrations in vapor extraction wills will likely marginalize the data to be obtained from a short-duration vapor extraction test. Clearwater recommends that the duration of the test be extended, with a not to exceed time limit established at five days of test operation. • Based on submitted information, Clearwater recommends that the methods for approved pilot testing be slightly modified to include a combined test, as specified in recent Clearwater letters. In addition to the combined test, slug tests would be conducted utilizing selected monitoring wells. Slug tests involve the rapid removal of a known volume of water from a monitoring well, usually with a large bailer, and the measurement of water recharge over a short period of time. Due to the fact that the Ruiz water supply well is completed at about 185 feet with an undetermined screened interval (personal communication with Stella Ruiz), it appears as if a pumping test using this well (as discussed in earlier letters) would yield no useful information.