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•� Work Plan for Refined Plume Definition and Management of Floating Product-7500 W ll ih St.. Tracy, CA. Page 12 ,r 5.0 DOWN-GRADIENT MIGRATION OF FLOATING PRODUCT SJC suspected the incipient arrival of LNAPL or "floating product" to water in Monitoring ... Well MW-7 from the results of the November 28, 2000 groundwater-quality monitoring round (The San Joaquin Company 2001£), due to the high concentrations of diesel and gasoline detected in the sample recovered from that well at that time. By September 11, �. 2001, the concentrations of both gasoline and diesel in groundwater in MW-7 exceeded the saturation concentrations for those fuels. When a measurement was made on April 11, 2002, the apparent thickness of LNAPL floating on the groundwater had reached 0.30 ft. Since that -- time, as is recorded in Table 3, floating product has continued to be present in that well through the latest round of groundwater-quality monitoring that was conducted on October 27, 2003, when it was measured to have an apparent thickness of 0.55 ft. Note: As is discussed in Section 9.2, floating product is being purged from Monitoring Well MW-7 on a quarterly schedule. After three rounds of purging on a weekly schedule, the first of which was performed on November 8, 2003, and one purging on a monthly schedule, the groundwater in that boring is currently essentially free of floating product. However, for the reasons discussed in this work plan, SJC does not believe that the area of the subsurface in the area around MW-7 is free of floating product. .�. 5.1 Initial Proposals for Removal of Floating Product Following discovery of the presence of significant thicknesses of floating product in Monitoring Well MW-7, SJC's engineers communicated their concern about its presence to SJCEHD staff. At that time, SJC recommended that action be taken to remove LNAPL from the subsurface in an extended area (Watkins 2002), Based on their extensive experience with w. management of floating product at fuel hydrocarbon release sites, SJC's engineers proposed that the LNAPL be removed by excavating trenches normal to the axis of the affected plume along the north side of West Eleventh Street so that the anticipated large volumes of floating product present in the area could be efficiently extracted from the subsurface by transfer into vacuum trucks for transport to and disposal at a permitted treatment and recycling facility. From conversations with SJCEHD's staff in 2000, SJC learned of that Agency's concern about the proposed method for removing floating product from the north side of West 4 Eleventh Street. Understanding that these concerns were based on that Agency's Iack of previous experience with the proposed technology and fears about its assumed high cost of implementation and its technical and economical feasibility, with the objective of providing a more complete technical explanation of the proposed remediation and, in the context of the cooperative approach between consulting engineers and regulatory personnel that has been advocated by the USEAP in its guidance documents (United States Environmental Protection ,.. Agency 1997), SJC requested a meeting with SJCEHS senior staff. The meeting was held on July 22, 2002, but following a limited technical discussion, SJCEHD's representative stated SJC