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`r ... 17 February 2006 AGE-NC Project No. 05-1256 Page 2 of 10 complex of the province have not been completely defined, but are believed to be of metamorphic and igneous origins. 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, located approximately `/z-mile south of the site. The estimated depth to ground water at the property is approximately 10 feet to 20 feet below surface grade (bsg), based on the map titled Lines of Equal Depth to Groundwater Spring 1999 published by the San Joaquin County Flood Control District and Water Conservation District(FCD&WCD). The map titled Lines of Equal Elevation of Groundwater Spring 1999, also published by the FCD&WCD, shows the property to be in an area where ground water flows toward the east- southeast, but this may be modified by changing recharge and discharge patterns. During AGE's subsurface investigation conducted in August 2005, ground water was encountered at a depth of approximately 18 feet to 20 feet bsg.Ground water is considered to be of beneficial use in California and is used for domestic, industrial, and commercial purposes. 2.2. PREVIOUS INVESTIGATIONS In January 2001, dispensers and product lines at the site were removed and upgraded. One soil sample was collected beneath each of four dispensers by Parker Environmental Services of Pittsburg and submitted for laboratory analysis,under the direction of EHD representatives.The samples were collected at depths between 1 foot and 2.5 feet bsg and were identified as follows: I @ 2-2.5'; 2 @ 0.5-1'; 3 @ 2-2.5'; and 4 @ 2-2.5'. Total petroleum hydrocarbons quantified as gasoline (TPH-g) were reported in each soil sample at concentrations ranging from 770 milligrams per kilogram (mg/kg; sample 3 @ 2-2.5') to 10,000 mg/kg(sample 1 @ 2-2.5'). Benzene,toluene,ethylbenzene,and total xylenes(BTEX)were reported in each sample at concentrations ranging from 0.64 mg/kg(toluene, sample 3 @ 2-2.5')to 1,300 mg/kg(xylenes,sample 1 @ 2-2.5').Methyl tertiary-butyl ether(MTBE)was reported in three of four soil samples at concentrations as high as 340 mg/kg (sample 2 @ 0.5-1'). Tertiary-amyl methyl ether (TAME) was reported in two of four samples at concentrations as high as 15 mg/kg (sample 2 @0.5-l').Di-isopropyl ether(DIPE),ethyl tertiary-butyl ether(ETBE),and tertiary-butyl alcohol (TBA) were not detected in any of the four samples collected and analyzed, however, detection limits for all samples were raised due to matrix interference. On 11 and 12 August 2005, a total of six soil probe borings (B 1 through 136)were advanced at the Advanced GeoEnvironmental,Inc.