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�i <br /> DeBoer Truck Lines, Inc. <br /> 201 West Sth Street, Ripon, Californic, September 9, 1999 <br /> . Phase I Report of Findings Page. b <br /> + 4 <br /> the valley. The coarser sediments which comprise the fans are mainly arkosic ii <br /> composition and were derived from erosion associated with glacial stages in the <br /> .;; mountains. The finer grained sediments are predominantly composed of rock flour <br /> washed out of the former extensive glaciers in the Sierras, (Ackley, 1964). <br /> The axis of the Central Valley Trough was a marshy, wet area throughout much of the <br /> Pleistocene Epoch. Lacustrine, flood plain and marshy depositional environments <br /> predominated along the axial portions of the trough, in the toe areas of the fans; <br /> throughout much of this time period. Coarser grained sediments of the upper portions o£ <br /> the fans occasionally prograded over the axial area of the trough in response to major <br /> F climatic changes in the Sierras. This has resulted in a predominance of fine grained silts! <br /> �-� and clays in the subsurface of the area. <br /> 7 0 Hydrology <br /> California and the .Federal Government have mandated that virtually all groundwater is;! <br /> beneficial for current or future use unless it can be demonstrated that no beneficial use is <br /> known. <br /> This aquifer is considered to be of beneficial use and as a result, must be protected from': <br /> contamination. Those identified uses include agriculture and industrial, as well as <br /> potential use for animal or human consumption.. <br /> 8,0 Conclusions and Recommendations �! <br /> I Three groundwater :monitoring wells were installed around the former underground diesel i! <br />+.: fuel storage tanks at the DeBoer Truck Lines site, Ripon, California. Soil analyses from <br /> the borings and the tank excavation samples show a soil contamination plume exists as <br /> .shown on Figure 7- Groundwater was encountered at 24.5 feet below ground level during <br /> the sampling event on 7127194. The floor of the tank excavation was at 25 feet and had <br /> diesel contamination of 4,100 mg/kg. Water samples from all wells were non-detect, but <br /> groundwater has probably been affected immediately below the former tank location. <br /> 'I <br /> Because the contamination is diesel fuel and the water table is shallow (25 feet), the most <br /> efficient remediation procedure would be to de-water the site through the existing wells <br /> and re-excavate to approximately 30 feet. The excavation should not encompass and <br /> destroy the wells and they could continue to monitor the groundwater. <br /> 'i <br /> ii <br /> i <br /> ,i <br /> I <br />