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BUILDING 16 FORMER USTs GROUND WATER INVESTIGATION WORK PLAN <br /> PORT WEST COMPLEX, ROUGH AND READY ISLAND,PORT OF STOCKTON <br /> 2.4.3 Ground Water Quality Monitoring <br /> Four monitor wells (MW-1, MW-2, MW-3, MW-4) were installed in August 1999. The monitor <br /> wells are completed to 10 feet bgs and the screen zone intercepts the sandy backfill material. <br /> As discussed above, the ground water collected from the monitor wells does not represent <br /> conditions in the native silts and clays. Ground water quality samples were collected and <br /> analyzed in August and November 1999, February and June 2000, and April 2004 (Table 7). <br /> The analytical results reveal declining concentrations over time. <br /> The most recent ground water samples did not reveal BTEX above the detection limit. Only the <br /> ground water collected from MW-1 revealed TPHg at 240 µg/1. Three wells revealed MTBE up <br /> to 140 µg/1. The interpreted distribution of TPHg and MTBE in shallow ground water is <br /> presented on Figures 14 and 15, respectively. <br /> 3. SCOPE OF WORK <br /> The previous investigations revealed measurable concentrations of petroleum hydrocarbons in <br /> soil in the location of the former USTs. The investigations also revealed petroleum <br /> hydrocarbons in ground water in the vicinity of the former USTs. The assessment of the <br /> ground water gradient indicates a direction toward the northwest to west-southwest. <br /> Based on the results of previous investigations and in accordance with the requirements of <br /> RWQCB, the purpose of this Work Plan is to characterize the distribution of petroleum <br /> hydrocarbons in ground water downgradient from the former USTs at the Site. The following <br /> scope of work has been prepared based on the recommendations in the Report and the <br /> requirements of the RWQCB. The scope of work consists of the following tasks: <br /> ■ Task 1 -Utility location, permitting, and health and safety plan <br /> ■ Task 2-Grab Ground Water Sampling <br /> ■ Task 3-Quarterly Ground Water Monitoring <br /> ■ Task 4-Reporting. <br /> All field work will be performed under the supervision of a California Registered Geologist. <br /> Environmental Risk Services,Corp. <br />