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y,. Report:Groundwater-quality Monitoring—January 26 2004: 7500 West Eleventh Street, Tracy, CA, Page 13 The pump inlet was attached to a flexible, transparent, 0.5-in diameter, plastic suction pipe. This permits the condition of the pumped fluid to be observed. The pump suction hose was connected to a 0.5-in diameter, 10-ft. long piece of rigid plastic pipe, or lance, which was lowered into the well until its tip was immersed below the surface of the floating product, but not to a depth significantly greater than the interface between groundwater and the floating product. The suction pipe and lance assembly includes a -b,„ regulating/shut off valve. The pump discharge line is also made from flexible, transparent, 0.5-in diameter plastic pipe. The discharge pipe directs the recovered product into the 55-gallon drum that is staged at the well head. Note: The purging of Well MW-7 that occurred on January 26, 2004 was conducted using the standard procedure described in Section 2.2 for purging wells at the 7500 West Eleventh Street site that is used preparatory to conducting a round of groundwater-quality monitoring. 3.3 Floating Product Removed to Date Since the first round of purging of floating product from Monitoring Well MW-7 occurred on November 8, 2003, when, prior to purging, the thickness of floating product in the well was 0.58 ft., five additional purgings of LNAPL from that well have been performed: November 15, November 22 and December 21, 2003 and January 26 and March 30, 2004. By November 22, 2003, no floating product was measurable on the I.-W groundwater prior to its being purged and no more than a sheen was observed on the extracted groundwater. After a delay of one month, less than one ounce of LNAPL was recovered from the well when it was again purged on December 21, 2003. Records of thicknesses of LNAPL that have been measured in Monitoring Well MW-7 are recorded in Table 3. As is described above, initially, floating product from Monitoring Well MW-7 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 15, 2003 purging, to achieve L a cost-effective operation, SJC reduced the purging frequency to once per month and, on December 21, 2003, to a quarterly frequency 3.4 Evaluation of LNAPL Removed from Monitoring Well MW-7 Compared to Estimated Volume in Subsurface +- It is instructive to review the results of the LNAPL-purging rounds that have been completed to date in the context of the likely effectiveness of that interim measure to influence significantly the mass of LNAPL present in the subsurface beneath the site. If it is assumed that the porosity of the Monterey sand filter pack around the slotted 2-in.- diameter casing of Monitoring Well MW-7 is 0.3, given the measured thickness of 0.58 ~- ft., then the total volume of floating product in the boring on November 8, 2003, b amounted to 0.07 ft3 (i.e., 0.52 gal.), which is the sum of the LNAPL in the casing itself A. sic