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Workplan for Additional Assessment and Feasibility Testing 3 <br /> 7-Eleven,Inc.Store No.20632,4627 DaVinci Drive,Stockton,CA October 17,2001 <br /> Selected soil samples from each borehole will be analyzed by a State-certified analytical laboratory for <br /> benzene, toluene, ethylbenzene and xylenes (BTEX), total petroleum hydrocarbons-as-gasoline (TPH-G) <br /> by EPA Method 8020/8015, and oxygenates MTBE, tert-butanol (TBA), diisopropyl ether(DIPE), ethyl-tert- <br /> butyl ether(ETBE), and tert-amylmethyl ether(TAME) by EPA Method 8260. Samples from the capillary <br /> fringe, significant lithologic changes, any areas of elevated PID readings, and total depth of drilling will be <br /> analyzed from the borings. <br /> All soil generated through drilling will be placed in Department of Transportation (DOT)-approved <br /> 55-gallon drums pending characterization and disposal. Water generated by steam cleaning will be <br /> temporarily stored on site in DOT-approved 55-gallon drums pending characterization and disposal. All <br /> waste will be disposed of as non-hazardous at a certified facility by a licensed hauling firm. The vertical <br /> delineation boring will be backfilled to surface grade with cement/bentonite and capped at surface to <br /> match surrounding grade. <br /> Vertical Delineation Groundwater Sampling <br /> The Simulprobe (and/or hydropunch)device will be used to collect discrete groundwater samples at <br /> depths of 20, 30, and 40 feet below grade to identify vertical concentration changes with depth below <br /> grade. The samples will be collected into 40-milliliter volatile organics analysis (VOA)vials, filled to zero <br /> headspace, acidified and kept on ice until delivery to a state-certified laboratory for analysis. Groundwater <br /> samples collected from the vertical delineation boring will be analyzed for BTEX and TPH-G by EPA <br /> Methods 8020/8015 modified, and oxygenates MTBE, TBA, DIPE, ETBE, and TAME by EPA Method <br /> 8260. Groundwater will also be monitored for electrical conductivity changes with increasing depth in <br /> anticipation of potential contact with brackish water known to be common in the region. <br /> Well Construction/Develooment/Gauging/Sampling <br /> The groundwater monitoring wells will be constructed with 2-inch diameter Schedule 40 poly-vinyl-chloride <br /> (PVC)casings with flush threads and 0.020-inch-slot well screen from 5-20 feet below grade. Sand filter <br /> packing will be placed around the well screen to a maximum height of 2 feet above the top of the screen. <br /> The filter packs will be sealed with 2 feet of bentonite (hydrated in place to prevent bridging)overlain by <br /> neat cement to surface grade. The wellheads will be protected at the surface by locking, expandable caps <br /> and traffic-rated street boxes (with watertight bolted lid)set in concrete. <br /> Following installation, the monitoring wells will be developed by hand bailing to remove fine-grained <br /> sediments from the well and filter pack. Water from the development process will be containerized and <br /> temporarily stored on site in DOT-approved 55-gallon drums. <br /> The top of casing of the wells will be professionally surveyed relative to a mean sea level datum, and <br /> gauged and sampled during the next quarterly monitoring event following drilling. <br /> 20632SAW.DOC <br />