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(up to 8,100 to 14,000 mg/kg at 10 to 11 feet bgs). This indicates that a source of contamination continues to exist in this area. Previous soil sampling indicated that TPHg concentrations up to 9,000 mg/kg extend to 25 feet bgs in this area. This is likely residual contamination present because the groundwater table was deeper than 25 feet bgs prior to the UST removal. Boring logs indicate that free product may be present in soil and groundwater within the former UST location extending to at least 16B-8 to the west and MW-3 to the east. Significant,but lower TPHg concentrations are present in soil (at the groundwater interface) and/or groundwater in borings 16-B10 to the south, and in boring 16B-7B and well EW-4 to the north. TPHg and benzene concentrations in groundwater drop off beyond this area in borings 16B-9 and 16B-11, but appear to be capillary fringe related. 6.1 Proposed Remedial Method Previous in-situ remedial systems have not removal the residual contamination around the former UST location. We propose to excavate the contaminated soil in this area as shown on Figure 3. The proposed excavation is 30' long by 28' wide by 22' deep. The proposed excavation would be extended to approximately 4-feet below the groundwater table in order to remove contaminated groundwater, and contaminated saturated soil. During excavation backfilling, oxygen release compound(ORC)would be mixed into the backfill below the groundwater table to assist with enhanced bioremediation of groundwater downgradient of the excavation. The excavation dimensions were determined after considering the previous and current soil and groundwater analytical data and the geologic and hydrogeologic data gathered during our recent investigations,as described below. Excavation contractors have stated that shoring will be required due to the depth of the excavation into saturated sands. Groundwater was measured at approximately 18 feet bgs in all 4 of the wells in the excavation footprint(MW-3,EW-3,EW-4 and VW-5). Similar stabilized groundwater depths were measured in our recent borings at Area 16. 9 25971014.DGD 7 April 2004