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1 <br /> Ults <br /> Ms Vicki McCartney,RENS Page 2 <br /> San Joaquin Environmental Health Department <br /> January 7,2004 <br /> borings (B-3,B-7, and B-8) were converted to dual completion vapor extraction wells(VW,1 <br /> through VW-3, respectively) (Delta, 2001). <br /> • October 1996: EMCON witnessed the installation of one vertical soil boring(B-9), <br /> subsequently converted to a monitoring well (MW4) (Delta, 2001). <br /> June—July 1999: Two 10,000-gallon, and one 8,000-gallon double-walled fiberglass gasoline <br /> USTs, associated dispensers, and piping were removed. In the same UST cavity two 20,000- <br /> gallon USTs, associated dispensers, and piping were installed. The excavations were backfilled <br /> with pea gravel. Analysis of soil samples taken from the UST replacement activities indicated <br /> total petroleum hydrocarbons as gasoline (TPHg), benzene, and methyl tertiary butyl ether <br /> (MtBE)contamination in the soil. (Pinnacle, 1999). <br /> • August 1999: The IT Group (IT) conducted a soil and groundwater assessment consisting of two <br /> cone penetration test(CPT)borings (CPT-2 and CPT-3)on the eastern edge of the site and one 5` ; <br /> CPT north of the site(CPT-1). Benzene and MtBE were detected in groundwater samples from 41re <br /> 1Z <br /> eIIQLo <br /> CPT-2 (Delta, 2001). s� Poshl- <br /> • September 2000: Delta conducted a soil vapor extraction test at the site. Three separate 4-hour Y`� <br /> tests were conducted. Soil vapors were extracted from well VW-lA, VW-2A, and VW-3A. The <br /> tests indicated that extraction of soil vapors from these wells at 9 to 10 cubic feet per minute <br /> (cfm), with 50 to 100 inches of water column ( WC),resulted in a radius of influence.between <br /> 34 and 45 feet. The initial hydrocarbon mass extraction.rates were calculated to be between 1.10 <br /> and 3.88 pounds of TPHg per day (Delta, 2000}. <br /> • 2001: Delta installed three monitoring wells (MW-5,MW-6, and MW-7). MW-5 is east of the <br /> site on American Street. MW-6 and MW-7 are in Oak Park,north of the site on the other side of <br /> Alpine Street(Delta, 2001). <br /> Site Geology and Hydrogeology <br /> The site is located in the northern portion of the San Joaquin Valley. The San Joaquin Valley is part of <br /> the Great Valley Province, which is a northwest-southeast trending asymmetrical structural trough. The <br /> San Joaquin Valley is a major California groundwater basin bordered by the Sierra Nevada Mountain <br /> Range to the east,the North Coast Mountain Range to the west,the Tehachapi Mountains to the south, <br /> and the Sacramento Valley to the northwest. The elevation of the site is approximately 15 feet above <br /> mean sea level. <br /> KAWprocessV5 BP ARCO\021861SVE System(new)12186 Workplan 03.doc <br />