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Soil Remediation Feasibility Study Work Plan - Unocal Station No 0187 April 30, 1996 groundwater beneath the site had been impacted by petroleum hydrocarbons. TPHg were detected in soil samples analyzed from borings U-1 (1.7 ppm at 26.5 feet bgs) and U-K (130 ppm at 41 5 feet bgs) TPHg were detected in soil samples analyzed from borings U-3 (330 ppm at 46 5 feet bgs), U-L (19,000 ppm at 45 5 feet bgs), and U-M (5 10 ppm at 45 5 feet bgs). Results of this subsurface investigation are presented in GSI Report No 4827.703-5, Well Installation and Exploratory Soil Boring Report, dated September 21, 1994. GSI performed a limited environmental site assessment (ESA) of the properties in the vicinity of the subject site The FSA identified a former station located at 448 East Miner Avenue, south of the subject site Historical groundwater data indicate that this former station is upgradient of the subject site. Environmental information related to the soil and groundwater conditions beneath this former service station were not obtained during the ESA. Environmental data related to surrounding properties in the vicinity of the subject site are discussed in GSI Report No 4827 04-1, Limited Phase I Environmental Site Assessment, dated May 11, 1995 To further assess on-site and off-site subsurface conditions, GSI installed three additional on-site groundwater monitoring wells (U-4 through U-6) and two off-site groundwater monitoring wells (U-7 and U-8), drilled two additional on-site exploratory soil bonngs (U-N and U-O), and installed one on-site vapor extraction well (UV-1) in August 1995 TPHg or benzene were not detected in soil samples collected from bonngs U-5 through U-7 or U-O TPHg was detected in the soil sample collected from boring U-N at 25 feet bgs (1.7 ppm). TPHg and benzene were detected in the soil sample collected from well boring U-4 at 10 feet bgs (41 and 0 011 ppm, respectively). TPHg was detected in the three soil samples collected from well boring UV-1 at 25, 35, and 40 feet bgs at concentrations ranging from 3,400 to 20,000 ppm Benzene was detected in the soil samples collected at 35 feet (99 ppm) and 40 feet bgs (15 ppm) in boring UV-1 Results of this subsurface investigation are presented in GSI Report No 4827 04-3, Well Installation and Soil Boring Report, dated October 9, 1995 Quarterly monitoring and sampling of the groundwater monitoring wells began in August 1994. Dissolved concentrations of TPHg or benzene are detected in wells U-1 through U-4, U-7, and U-8 During the most recent sampling event (February 1996), TPHg concentrations ranged from 51 to 36,000 parts per billion (ppb) Benzene concentrations ranged 3 2 to 3,700 ppb The highest concentrations of both TPHg and benzene were detected in well U-3 Quarterly sampling and monitoring of the wells is performed by MPDS Inc. Historical groundwater chemical analytical data are summarized in the most recent MPDS report (no. MPDS-UN0187- 07, Quarterly Data Report, dated February 27, 1996) UMI"saw 4WAS-1 3