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,y f ' 10 September 2004 AGE-NC Project No 04-1129 ` ' Page 3 of 7 li i [I 23 PREVIOUS SITE INVESTIGATION ACTIVITIES Previous site assessments on the property include • February 2002 - A geotechnical investigation was conducted at the site by Raney Geotechnical Inc (RGI){During the course of the investigation, soil samples collected from tA' 4V ; two borings (B4 and B5)were noted as having a"gasoline odor" ry - May 2002-One soil boring(B-5)was advanced near the former UST area by Construction Testing & Engineering, Inc (CTE) to determine the nature and extent.of soil possibly ' Impacted by petroleum hydrocarbons Soil samples collected from soil boring B-5 contained concentrations of total;Ipetroleum hydrocarbons quantified as gasoline (TPH-g), diesel ' (TPH-d)and/or motor oil(TPH-mo) The highest detected concentrations were found in soil I s samples collected at depths of 10 and 15 feet below surface grade (bsg), respectively, I however,additional laboratory analysis of the 15-f6ot sample from bonng B-5 did not detect ' volatile organic compounds (including benzene, toluene, ethylbenzene and total xylenes [BTEX] and methyl tertiary-butyl ether [MTBE]) or polychlorinated biphenyls • Subsequently, a geophysical (magnetometer) survey of a portion of the site was performed to locate potential anomalies(underground storage tanks[USTs]or other buried structures) • .July 2002-Exploratory trenches were excavated near the UST area utilizing a backhoe and two soil probe borings (PB-2 and P13-3) were advanced.at the site, the trenches were excavated at locations identified during the magnetic survey as possible USTs or buried structures The eastern trench contained assorted waste material and excavated soil had a- petroleum hydrocarbon=like odor and appeared to be stained, soil samples from the soil borings did not contain detectable concentrations of petroleum hydrocarbons at the depths sampled Petroleuin hydrocarbons and volatile organic compounds were detected in.a grab iground water sample collected from soil boring PB-2 at concentrations of 270 micrograms ;I per liter (µg/l) TPH-g, 2 6 µg11 toluene, 2 3 µg/1 ethylbenzene, 27 6 pg/1 total xylenes, 3 7 pg/l napthalene„1 1 1:g/1 n-propylbenzene, 14µg/11,2,4-tnmethylbenzene,4 1 µg/l 1,3,5- tnmethylbenzene and i':2 µg/1 n-butylbenzene, however, the detected concentrations of I VOCs do not exceed th'e state of California Department of Health Services' Maximum I Contaminant Levels and Action Levels • November 2002 - Two 'USTs (UST-1 and UST-2) were discovered during excavation of debris and hydrocarbon-impacted soil The two USTs were single-walled and appeared to be constructed of redwood with steel banding, the tanks were contained in separate back vaults with concrete floors Each lank had an approximate capacity of 15,000 to 20,000 . gallons Upon discovery of the tanks, the San Joaquin County Environmental Health Department (EHD) was notified and the tanks were removed under permit Based on analytical results of soil samples collected from beneath the tanks, it appears that the tanks [ Advanced GeoEnveronmeatal,Inc