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is Work Plan for Additional Subsurface Assessment and Remedial Action—Former Unocal Station#2859 December 11,2001 KB-5 at approximately 20 feet below ground surface (bgs) at up to 239 and 370 parts per million (ppm), respectively, and benzene was detected in the two borings at concentrations up to 11.2 and 6.58 ppm, respectively. In 1988, two 10,000-gallon gasoline USTs and one 550-gallon waste oil UST were removed. Soil samples collected from the base of the tank pit contained TPHg and benzene at concentrations up to 13 and 0.29 ppm, respectively. Between June 1988 and February 1992, seven monitoring wells (MW-1 through MW-7), three vapor extraction wells (VW-1 through VW-3), and one soil boring were installed by Applied Geosystems and RESNA. The highest TPHg and benzene concentrations reported were from an area around the northern product island location at up to 17,300 and 28 pprn, respectively. A soil vapor extraction test was conducted by RESNA in 1992. The test showed that a wellhead flow rate of 43 cubic feet per minute and an estimated radius of influence of approximately 25 feet could be achieved. In July 1994, Pacific Environmental Group, Inc. (PEG) installed monitoring wells MW-8 and MW-9. Groundwater samples from the wells were non-detect for benzene, but TPHg were detected in wells MW-8 and MW-9 at concentrations of 93 and 110 parts per billion (ppb), respectively. PEG performed a six-month on-site vapor extraction pilot study in 1996. During that study, approximately 2,745 pounds (450 gallons) of TPHg and 12 pounds (1.6 gallons) of benzene were removed. ARCADIS Geraghty &Miller, Inc. installed wells MW-10 and NP-I in January 1999. Soil samples from well NP-1 showed impact beneath the site between 40 and 60 feet below ground surface (bgs). The highest TPHg and benzene concentrations were from a sample at 60 feet bgs at 290 and 5.8 ppm, respectively. Discrete grab groundwater samples from well boring NP-1 had concentrations of TPHg and benzene in samples collected between 50 and 70 feet bgs. The highest concentrations of TPHg and benzene detected were 200,000(50 feet bgs) and 21,000(60 feet bgs) ppb,respectively. Groundwater Monitoring and Sampling Quarterly groundwater sampling started in June 1988. Separate phase hydrocarbons have not been observed in the wells. Since monitoring of the wells began in the first quarter of 1993, groundwater beneath the site has risen more than 20 feet. In the most recent monitoring and sampling event on August 16 and 17, 2001, depth to water in the wells ranged from 23.30 to 26.33 feet below top of casing. Groundwater flow during this event was to the northeast at an approximate gradient 0.002 to 0.005. The groundwater flow direction and gradient are consistent with historical data. During the August 16 and 17, 2001 event, TPHg range hydrocarbons were reported in wells MW-2 (98,000 ppb), MW-10 (150,000 ppb), MW-11 (34,000 ppb), MW-12 (1,800 ppb), and MW-15 (3,100 ppb). Benzene was reported in wells MW-2 (5,000 ppb), MW-10 (5,000 ppb), MW-11 (850 ppb), 240072.06 2