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�. ,« t' Ms. Diane Lundquist October 8, 1990 Page 4 Water bevel MeasurementyFlow Air•ectiart,and lTti•drnulic Gradient Water level measurements made since December 1989 are compiled in Tabic 3. Depth:o ground water beneath the site ranged from 30.09 to 31.86 feet, as recorded on July 31, 1990. Water level measurements indicate an inferred direction of ground water flow toward the north as indicated in Figure 3,with a hydraulic gradient of approximately 0.01 foot per font, Monitoring wells containing free product were not used in determining the hydraulic gradient. Free product thicknesses recorded in the various monitoring wells are provided in Table 3. Under round_Piping Wark During service station reconstruction work performed at the site,seven monitoring wells at the site were manifolded together to provide for future soil vapor extraction. In addition,five of the seven monitoring wells were manifolded together to provide compressed air and water discharge piping to allow for ground water extraction in the future. Design assumptions and detailed design considerations were presented previously in Delta's Interim Remedial Action Plan and Proposed Schedule Letter,dated April 13,1990. Free-Phase Petroleum Product RewyeEl and Iuterlm Remedial Action A site visit on December 12, I989, revealed the presence of approximately 4S feet of free-phase petroleum product (product) in monitoring well MW-2. Weekly bailing of product from MW-2 rermvered approximately 41 gallons of product,but did not significantly reduce product thickness. To im<re=product recovery,a Westinghouse air-operated bladder pump, coupled to a floating product skimmer,was installed in MW-2 on April 13,i990,to continuously recover product. Recovered product is touted to drums located at the remedial equipment area through the previously installed piping system. The product storage drums are underlain by a double containment system and the storage drums are equipped with a tank full shutoff to shut off the air compressor supply to the pump if the drum is full. A detaited layout of the remedial equipment area showing the location of the product storage drums and also the air compressor is presented in Figure 4. To provide electric power for the air compressor and also for future remedial equipment installation, a 200-amp temporary electrical service was installed during service station remodeling. The electrical panel installation details are presented in Figure 5. A complete description of the 57ee-phase petroleum product recovery system can be found in Delta's Interim Remedial Action Plan and Proposed Schedule letter,dated April 13, 1990. The product recovery system has been checked once every 2 weeks for the parameters involving the amount of product in the product storage drums, air compressor information, and product pump information. The system has operated for a total of 86 days as of August 7, 1990. During those operating days,the system has recovered approximately 136 gallons of product. Table 4 presents the operation history of the interim recovery system. Due to system maintenance,the system had been off intermittently for a total of 31 days since it had been installed Table 5 presents the system's nonoperation history and the reasons for each shutdown. As of August 7, 1990,a total of 177 gallons of free-phase petroleum product has been removed. Source Test To fully evaluate the remedial effectiveness of ground water pumping and soil vapor extraction at the site,a source test was conducted on May 20 and 21, 1990. The initial part of the source test consisted of continuous pumping of ground water from monitoring well MW-7 for a period of 24 hours (the pumping operation lasted a total of 34.5 hours). A sustained ground water pumping rate of 0,1 gallon per minute(gpm)was accomplished with a drawdown of 2.4 feet from the static water level.