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1 'FAACEINNURC volcanic rocks, which range considerably in age and composition To the west of the valley are the Coast Ranges, which are composed of metamorphic rocks of the Franciscan Formation Structurally significant features in the Site area include the Stockton Fault, which trends ' northeast-southwest and is approximately eight miles northwest of the Site, and the Midland Fault Zone, which trends north-south and is approximately 25 miles northwest of the Site The San Andreas fault zone is approximately 50 miles west of the Site The soils beneath the Site characterized during the February 1993 drilling (Wallace-Kuhl) 1 consisted of fine sands and silt/sand mixtures to approximately 50 feet below ground surface (bgs) Below this depth, a fine to coarse sand and silty clay are present Similar soils were reportedly observed to a depth of 15 feet bgs during removal of the USTs in 1990 1 1.3 Hydrology The Site has been graded and modified to promote surface drainage Catch basins collect rainwater for flow north through underground pipes into the adjacent airport storm water system Surface drainage is to Little John Creek, a water course oriented east-west, approximately 1 5 miles north of the Site Little John Creek flows into Camp Slough and eventually into the San Joaquin Raver Groundwater was encountered during drilling in February 1993 at depths ranging from 46 to 49 feet bgs Groundwater measurements made in the wells on February 24, 1993 indicated a ' static groundwater surface of approximately 45 feet bgs The groundwater flow direction beneath the Site was calculated to be to the northeast with a hydraulic gradient of 0 001 feet/foot (ft/ft) The depth to groundwater in the three monitoring wells, MW1, MW2, MW3, on September 5, 1996 was 43 96, 44 05, and 43 77 feet bgs, respectively The hydraulic gradient ' was calculated at 0 003 ft/ft flowing to the northeast The gradient is consistent with the calculated gradient for the previous quarter, however, the direction has changed slightly from northwesterly to northeasterly Versar believes this reflects seasonal fluctuations in the igroundwater flow Groundwater elevations and gradient are included in Table 1 and shown on Figure 3 r i 2 i