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Work Plan for Refined Plume Definition and Management of Floating Product-7500 W 11th St„ Tracy, CA. Page 3 �.; same time that the tanks were removed from the site, soil heavily affected by fuel hydrocarbons was excavated from beneath the pump island area and 521.25 tons of that material was disposed off-site at a permitted facility. In addition, some 2,000 gallons of Light •.. Non-aqueous Phase Liquid (LNAPL) ("floating product") and affected groundwater were removed from the subsurface by pumping from a tank pit into a vacuum truck, which was used to transport it to a permitted recycling facility (Dietz Irrigation 1999a). The locations of +- the pits from which the tanks were extracted are shown on Figure 3. The effectiveness of the soil remediation and floating product removal achieved at the time the tanks were removed from the site in reducing groundwater contamination in the area around the pump islands, where the preponderance of the fuel hydrocarbons affecting the subsurface beneath the 7500 West Eleventh Street property itself were released, can be y- assessed by inspection of Table 2. That table includes the concentrations of analytes of concern found in samples of groundwater recovered from Monitoring Wells MW-3 and MW- 4 over the period from May 11, 2000 to October 27, 2003. As is shown on Figure 2, those monitoring wells are no more than a few feet down the groundwater gradient from the on-site areas where at least several inches of product was found floating on the water table. However, because the floating product had been removed from a wide area of the subsurface when it was pumped out of the tank pit, no LNAPL was detected in those wells when they were first sampled and, since that time, there has been a marked decline in the concentrations of analytes of concern in samples of groundwater recovered from them. 2.4 Interim Measures for Removal of LNAPL from Area around MW-7 As is detailed in Section 9.2, to comply with the directive issued by SJCEHD (San Joaquin County Environmental Health Department 2003), interim measures to remove floating product from the subsurface in the area around Monitoring Well MW-7, which is located, as shown on Figures 2 and 4, on the north side of West Eleventh Street, were initiated on November 8, 2003. Initially, floating product was purged on a weekly basis. However, since a significant thickness of floating product failed to reappear in the well seven days after the November 15th purging, SJC hopes to reduce the purging frequency to once per month, or such longer period as might be necessary to achieve a cost-effective operation. Purging is to continue until such time as a larger-scale floating product removal system is constructed, or floating product ceases to be present in that well. sic