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Beacon Station No.474 December 28, 1998 3440 Fast Main Street Stockton California Amendment To Work Plan samples will be collected from this depth and analyzed as described above for ✓ boring B-7 in Task 2.1. If soil boring B-8 encounters hydrocarbon-impacted soil in the vadose zone and hydrocarbon-impacted soil or groundwater at or near the historical low .3 groundwater level, a 2-inch diameter PVC well (MW-13) with 5 feet of 0.020- inch screen will be installed across the lowest impacted interval. If well MW-13 is constructed across the lowest impacted interval, an adjoining boring (B-8A) will be drilled within 5 feet of boring B-8 to facilitate the installation of the deep groundwater well. Because of the proximity of boring B-8A to B-8, this boring will be drilled without the collection of soil samples to the approximate depth of 55 feet or less. Based on analytical data, one or possibly two 2-inch diameter PVC vapor extraction wells with 0.020-inch factory- machined slots will then be installed as a single or dual completion in boring B-8A. If soil boring B-8 encounters no hydrocarbon-impacted soil in the vadose zone, and encounters hydrocarbon-impacted soil or groundwater at or near the historical low groundwater level, a 2-inch diameter PVC well (MW-13) with 5 feet of 0.020-inch screen will be installed across the deepest impacted interval in the 8-inch diameter boring. If soil boring B-8 encounters no hydrocarbon-impacted soil in the vadose zone and no hydrocarbon-impacted soil or,,groundwater at the historical low groundwater level, the boring will be uteri-from~thtotal depth--to—the surface. '` "` v Task 2.5: If soil borings B-7 and B-8 do not encounter hydrocarbon-impacted soil or groundwater at or near the historical low groundwater level, it will not be necessary to drill and sample boring B-9. If soil-boring B-8 encounters hydrocarbon-impacted soil or groundwater at or near the historical low groundwater level, the 8-inch diameter soil boring B-9 will be drilled and sampled east of the dispenser islands (Figure2). If the discreet groundwater samples collected at the historic low water level in boring B-9 are impacted, a 2-inch diameter PVC well (MW-14) with 5 feet 0.020- inch screen will be installed across the deepest impacted interval. o vapor extraction wells will be required in this boring, as th existing vapor extraction r~ wells should be sufficient to affect this area of the site Tasks 3 and 4 are unchanged from the original work plan. 1474-22.awp 3 HORIZON ENVIRONMENTAL INC.