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i l I Interim Migration Control Plan-Tosco 76 Branded Facility No. 11193 April 19 2000 thereby eliminating exposure risks and other negative impacts of on-site treatment of hydrocarbon impacted groundwater. Groundwater removal from monitoring wells MW-1 and MW-2 would have a minimal impact on the existing service station operation and its patrons and can be implemented immediately following written regulatory concurrence. The groundwater will be purged directly from the monitoring wells into 5,000 gallon vacuum trucks and transported by Onyx Industrial Services, Inc., of Benicia, California (Onyx), to the Tosco Refinery, in Rodeo,California, for disposal. Groundwater samples will be collected from monitoring wells MW-I and MW-2 prior to initiating the purging program and periodically thereafter. The results of these samples, in conjunction with the results from quarterly groundwater monitoring and sampling of the ten existing and proposed wells, will be used to evaluate the effectiveness of the groundwater purging. Based on this evaluation, recommendations for modification of this IMCP, including further performance testing and/or the purging of additional on-site monitoring wells will be made as warranted. Groundwater sampling outside of normal groundwater monitoring and sampling activities will be conducted in accordance with GR Field Methods and Procedures (attached). All groundwater samples collected from wells MW-1 and MW-2 will be submitted to Sequoia Analytical (Sequoia), in Walnut Creek, California (ELAP 91271). The monthly groundwater samples will be analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tert-butyl ether (MtBE) by EPA Methods 8015 (modified)/8020. Analytical results will be documented in status reports to be submitted to Tosco and the SJCEHD. In conjunction with the initial groundwater purging event, GR proposes to collect groundwater level readings from the nearby on-site monitoring wells to assess the influence of groundwater purging on the surrounding wells. During purging, GR personnel will collect depth-to-water (DTW) readings from existing on-site monitoring wells MW-3, MW-4, and MW-5 and vapor extraction well VW-I (Figure 2). In addition, any on-site wells that have been recently installed by Cambria (as proposed in their February 25, 2000 work plan) will be utilized. DTW readings will be continuously collected, beginning prior to initiation of groundwater purging until groundwater levels have stabilized after completion of purging activities. Groundwater drawdown data from this perfomance test will be tabularized, and a qualitative estimate of the radius of influence and the degree of migration control afforded by the weekly purging will be made and presented in the first status report. SCHEDULE Implementation of this IMCP can begin immediately upon receipt of regulatory approval t4om5.04-t 2