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Ms. Diane Hinson -2- 25 May 1989 We realize that the installation of these vapor recovery wells means they are proposing a soil remedial action plan prior to identifying the problem, but it is pretty straight forward approach and at their own risk. Operation of the system could not begin until they know where the soil problem is relative to the leak source and ground water. Installation of Proposed Ground Water Monitoring Wells 1 . We still recommend that an additional monitoring well be installed near the southeast corner of the Kettleman Lane-Hutchins Street intersection. Brown and Caldwell 's suggestion that �W-4 and MW-5 are sufficient to define the plume is incorrect. For one thing, in January 1989, MW-5 contained benzene above the State Action Level (1.0 ppb) . For another, MW-4 is approximately 300 feet from the proposed extraction well location near MW-2. The zone of capture for the recovery well (s) eventually installed at this site must be able to capture the entire area defined by the "zero line". At the same time it is unacceptable to capture a large amount of water from outside the plume. We therefore, request that the plume be defined as accurately as- possible so a reliable and effective remedial system can be implemented. 3. We accept ARCO's request to sample on4y W-2B (not W-2 and W-2B) on a monthly basis, but in addition to BTX&E, TPH analysis is to be performed. 4. We have no objection to replacing MW-1 with a new monitoring well . The proposed depth and screened interval of this well is the same as the other proposed monitoring wells and those in monitoring wells MW-2 and MW-3 (screened from approximately 40 to 70 feet below the surface) which is important for correlating data between wells. If you have any questions, please call me at (916) 351-5725. EDWARD W. JA ES Engineering Geologist EWJ:ewj