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I 17 September 2001 AGE-NC Project No. 98-0468 Page 4 of 7 advanced east of the former UST area to evaluate previously reported anomalous ground water analytical results in the vicinity of monitoring well MW-1,and soil probe boring SB-1. Soil.borings B-3 was completed west of previous soil probe boring SB-6 and the former UST area. -There were no reported detections of BTEX, TPH-g, or TPH-d in-soil samples collected from the five soil borings(Table 5). Fuel oxygenating compound MTBE was detected at concentrations of 65 ug/mg,. and '110 ,ug/mg in soil samples collected from soil boring MW-4 at 17.5 and 20 feet bsg, respectively. Between June 1994 and the June 200 1,eight-ground water monitoring wells have been installed and sampled for petroleum hydrocarbons. The lateral extent of the petroleum hydrocarbons is limited by well MW-7 and MW-8, down-gradient from the.former UST area. While the vertical extent of the dissolved MTBE impact to ground water has not been defined by the current well network. 2.3. REGIONAL GEOLOGIC/HYYDROGEOLOGIC SETTING The property is situated within the-Great Valley Geomorphic Province of California, a large, . elongate, northwest trending; asymmetric structural trough. The Great Valley Province.has been filled with thick sequences of,sediment-ranging in age from Jurassic to Recent, creating a nearly flat- lying alluvial pWn,.extending from the Tehachapi Mountains in the-south to the Klamath Mountains in the north. The western and eastern boundaries of this province are the California Coast Range and the Sierra Nevada, respectively.Rocks composing the basement complex of the province have not been completely defined but are believed to be of metamorphic and igneous origins. The northern and southern portions of the Great Valley Province have been designated the Sacramento and San Joaquin Valleys, respectively. . , The Modesto, Riverbank and Turlock Lake'Formations and overlying recent alluvium are. the principal source of domestic ground water in the 13,500-square-mile San Joaquin Valley Ground Water Basin (Basin 5-22)..This basin is drained primarily by the San Joaquin River. The nearest surface water feature in the vicinity of the property is the San Joaquin River approximately one-half mile south of the site. f 2.4. GROUND WATER DEPTH AND FLOW DIRECTION Based on data acquired from a previous investigation at the site,the estimated depth to ground water in the vicinity of the"siteis 10 to 12 feet below surface grade (bsg). Based upon.data obtained from nearby sites, the prevailing ground water flow direction in the•vicinity of the site is estimated to.be north to northeast. However,,flow direction.maybe both locally.and seasonably variable. Advanced GeoEnvironmental,Inc.