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- I <br /> I <br /> Former Stockton Scavenger— Site Summary <br /> 1988 — Biosystems International — assessment of soil and groundwater 10 <br /> borings <br /> TPHd and oil at 20 ft to N of former diesel tank <br /> • Hydrocarbon detections at 30 ft (water table) <br /> Sept 1992 - removal of 2.diesel USTS (10K and 7.5K) and 1 gasoline UST <br /> (7.5K) <br /> Nov 1992 — Mark Group assessment <br /> • 5 soil borings l <br /> • Soil ND for TPHg and TPHd, one 0.04 mg/kg BTEX detection <br /> • Groundwater, benzene and toluene `above action levels <br /> • Recommendation for soil overexcavation <br /> Soil excavation (Mark Group - date?) <br /> 2 500 d3-im acted soil excavated landfill <br /> • Y p disposal <br /> • Missing confirmation soils data — Mark Group Preliminary Closure <br /> Report states localized areas of remaining impact where excavations <br /> terminated due to building proximity <br /> June 1994 — Mark Group Preliminary Closure Report <br /> missing soils data have partial report <br /> • Recommended NFA on soils based on excavation and removal <br /> • Conducted additional assessment that verified localized groundwater <br /> impacts and began quarterly monitoring <br /> • Implemented groundwater extraction from MW-2 <br /> 1994 to 1997 Groundwater extraction <br /> • MW-2 extraction and carbon treatment— <br /> • 591,000 gallons extraction, 101bs TPHg 2.1 lbs TPHd 2.5 lbs benzene <br /> Soils <br /> • primarily clay and sandy clay with localized clayey sand lenses <br /> Groundwater <br /> • 1988 encountered approximately 30 ft bgs <br /> • 1994 first-encountered 41 to 44 ft bgs, stabilized at 31 ft bgs <br /> • 2008 approximately 14 ft bgs. <br /> • MW-1 through MW-4 screened 28.5 to 48 ft bgs <br /> • Screens submerged —14 ft and submerged since 1994/95 <br /> • Decreased concentrations over monitoring history, currently (April 08) <br /> benzene MW-2 at 0.81 ug/L and 1,2-DCA MW-4 at 0.92 ug/L <br /> i <br /> i <br /> I <br />