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period of 15 months. MW-DIS-3 is likely to be well aerated and therefore not <br /> electron-acceptor limited. <br /> Site Character Summary <br /> Groundwater at the Disco site has a very small horizontal gradient (0.001 ft/ft) and a more <br /> significant vertical gradient of 0.012 ft/ft. The natural rate of horizontal movement is perhaps <br /> 5 to 10 feet per year, and the vertical gradient is an order of magnitude slower. The direction <br /> of the horizontal shallow gradient has been highly variable in 3.5 years of monitoring. <br /> Historic fluctuations in groundwater elevation of over 50 feet since closure_of the Disco <br /> Service Station (20 years ago) are likely to have smeared NAPL gasoline both above and <br /> below the present groundwater elevation. Groundwater is probably on the rise due to extreme <br /> precipitation/infiltration this winter. Vertical groundwater fluctuations in combination with.a <br /> variable horizontal gradient have spread gasoline and created a groundwater plume that has <br /> migrated approximately 200 feet to the west and north west and 100 feet to the east. <br /> Groundwater modeling indicates that the shallow groundwater at-the Disco site is not likely <br /> to have been influenced by.former Del Monte production well pumping. Groundwater wells <br /> in the area are all screened well below the A and B Zones because of the low yield of these <br /> formations. <br /> i <br /> i <br /> r 1 <br /> i <br /> SFO]0030982.DOC 3-24 <br />