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31 October 2007 AGE-NC Project No. 07-1524 Page 2 of 10 The Modesto, Riverbank and Turlock Lake l'onnations 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 site is the Stockton Deep Water Channel, approximately '/a-mile toward the south. The prevailing ground water flow direction in Stockton generally ranges from northeast to east, but this may be greatly modified by local recharge and discharge patterns.Ground water monitoring data taken at several nearby monitoring sites in the 4" Quarter 2006 showed shallow ground water at 10 to 14 feet below surface grade (bsg) and with a general flow direction towards the northeast. Ground water is considered to be of beneficial use and is utilized for domestic, industrial and commercial purposes. 2.2. UNDERGROUND STORAGE TANK REMOVAL It is our understanding that one 1,000-gallon leaded gasoline, steel-UST was removed in May 1990. An EHD approval UST removal permit was issued in June 1990 and the removal was brought into compliance.It does not appear that confirmation soil sampling was performed at the time of removal. 2.3. PREVIOUS SITE ASSESSMENT On 24 July 2007. one soil probe boring (B1) was advanced in the former UST area. Discrete soil samples were collected at 5-foot intervals, beginning at 5 feet bsg, to the total depth of the boring at 20 feet bsg. In addition, one grab ground water sample was collected from boring B 1 at total depth. TPH-g and BTEX compounds were detected in soil sample B1-10 at concentrations of 560 milligrams per kilogram(mg/kg), 0.030 mg/kg,0.50 mg/kg, 8.8 mg/kg,and 43 mg/kg, respectively. TPH-g and BTEX compounds were detected in the grab ground water sample B-1 W at concentrations of 2,200 nil crograms/1iter(pg/1), 3.0 µg/l, 9.3 ltg/l, 240 ltg/l, and 710 µg/1. respectively. Analytical results of soil and ground water samples are summarized in Tables I and 2. 3.0. SCOPE OF WORK Based upon the analytical results of soil and ground water samples reported in a previous investigation,the EHD has required further investigation to determine the lateral and vertical extent of hydrocarbon-impacted soil and ground water. One CPT soil boring will be advanced and selected Advanced GeoEnvironmental,Inc.