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3 <br /> MM- i <br />�m <br /> Six groundwater monitoring wells were installed in the 6 <br /> �. exploratory borings. Lithologic and well construction logs <br /> are available for each of these wells. The location of <br /> N these wells are shown on Figure 2. <br /> r <br /> Groundwater was encountered between 13 and 17 feet below <br /> grade. water .levels rose to approximately 8 feet shortly <br /> after drilling and have fluctuated between 8 and 10 feet <br /> �• below grade. The groundwater gradient has fluctuated in <br /> both direction and magnitude (Table 2). These changes may <br /> be attributed to pumping in the area or influences from the <br /> Mokelumne River which lies approximately one-half mile to <br /> .� the east. The predominate gradient direction is westerly <br /> with a magnitude between 0.002 and 0.007 ft/ft. <br /> Free flowing product was not detected in any of the six <br /> wells on site. Groundwater sampling performed during the <br /> site investigations and quarterly sampling program has shown <br /> - high levels of gasoline constituents in one well (MW--4) and <br /> low to moderate levels in three wells (MW- 1, MW-3, MW-6) <br /> (Table 3) . High levels of oil and grease were also detected <br /> in MW-1. It appears. that the oil and grease was not related <br /> to the underground tanks, but caused by surface leakage into <br /> the well. This problem was repaired by raising the <br /> watertight traffic box and installing a locking watertight <br /> well cap. Resolution of this problem will be confirmed with <br /> future sampling events, <br /> 2.0 SITE DESCRIPTION <br /> 2.1 Topographic and Cultural Features <br /> The project site lies on generally flat ground. Cultural <br /> features, including adjacent home and structures, are <br /> depicted on Figure 2. <br /> 2.2 Hydrogeologic Setting <br /> The project site lies at the southern end of the Sacramento <br /> - Valley, part of the large northwest trending asymmetric <br /> structural trough termed the Central Valley of California. <br /> The Sacramento Valley contains a thick sequence of sediments <br /> which, in places, reach a depth of 10 miles. These <br /> sediments range in geologic age from Jurassic (205 million <br /> years before present) to Holocene (present time) and include <br /> both marine and continental rocks and deposits (Page, 1989). <br /> The project site is located on Holocene river deposits that <br /> have been produced by the nearby Mokelumne River and its <br /> ancestor channels. According to the California Department <br /> -of_Water__Resources-_(_1978, p.__3.3) these river deposits attain <br /> a maximum thickness of approximately 115 feet and are the <br /> most permeable deposits in the Sacramento Valley. <br /> inr 2 <br /> i <br />