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Supplemental Investigation Report,Problem Assessment Report and Work Plan <br /> Cleanup and Abatement Order No 5-00-707 EAI Prosect No 1232 <br /> In September 1998, Environmental Resolutions, Inc (ERI) performed measurements of ground <br /> water elevation in wells MW-3, MW-4, MW-11, MW-15, and MW-17 during RIW pumping <br /> ' and non-pumping periods (see ERI, 1999) Data from this work indicates that all wells <br /> exhibited a decrease in ground water elevation during the pumping period, with a maximum <br /> decrease of 1 83 feet in well MW-17, which is closest to the RIW <br /> ' In 1999, ERI drilled exploratory borings B1 and B2 to a depth of 80 feet b s and installed wells <br /> p r}' S P g <br /> MW-10A, MW-14A, MW-18, MW-19S, MW-19D, MW-20S, MW-20D, MW-21S, MW-21D, <br /> MW-22S and MW-22D (see Figure 4) <br /> In May 1999, ERI drilled and installed two additional cluster wells MW-20S, and MW-20D at <br /> locations shown in Figure 4 The analytical result of soil samples is included in Table 2, <br /> description of wells in Table 3, and ground water testing results in Table 4 <br />' 2 3 3 Ground Water Monitonn� <br /> Ground water monitoring at the Unocal site has been conducted since 1985 Table 4 <br /> summarizes the results of the ground water testing, and Table 5 contains ground water <br /> elevation data <br /> 2.4 Commingled Plume <br /> Unocal and Wards have agreed that a commingled plume exists between the two contributing <br /> sites, i e , 5400 Pacific Avenue and 5606 Pacific Avenue, and that work associated with <br /> Cleanup and Abatement Order No 5-00-707 will be completed jointly by Unocal and Wards <br /> The San Joaquin County Public Health Services, Environmental Health Division concurred in a <br /> letter dated November 24, 1999 that a commingled plume exists between the Wards and <br /> Unocal sites <br /> B13 12321 IRW-WP -8- <br /> ENVIRDNMENTAL AUDIT, INC-0 <br />