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u "..1 Stec 76(Former BP)Service Station No. 11192 March 10,2011 Page 2 Properties in the site vicinity are primarily residential and commercial developments. A former Shell Service Station was located across Pershing Avenue, east of the site (1267 Country Club Boulevard). OVERVIEW OF GEOLOGIC AND HYDROGEOLOGIC CONDITIONS Based on a review of historical boring and CPT logs, previous assessments have indicated that soil beneath the site and site vicinity generally consisted predominantly of silt and clay containing some layers of mixtures of sand/clayey sand to the total depth explored of 140 feet below ground surface (bgs). Shallow A Zone wells MW-1 through MW-4, MW-8 through MW-10, MW-12, and MW-13 were completed to depths ranging from 28 feet to 30 feet bgs. Intermediate B Zone wells MW-5 through MW-7 were completed to depths ranging from 40 feet to 45 feet bgs. Historical depth to water (DTW) groundwater levels in the A Zone and B Zone wells have generally ranged from approximately 12 feet to 17 feet bgs. An approximately 32-foot thick layer of clay was encountered during the drilling of on-site boring MW-11 from approximately 37 feet to 69 feet bgs; this deep C Zone well was completed with a well screen penetrating a silty sand/sand layer from approximately 69 feet to 79 feet bgs. Historical DTW groundwater levels in MW-11 have generally ranged from approximately 17 feet to 19 feet bgs. SITE HISTORY AND PREVIOUS INVESTIGATIONS In order to facilitate the sale of the property to BP, Mobil retained Target Environmental Services, Inc. to perform a soil gas survey in March of 1989. Benzene, toluene, ethylbenzene, and xylenes (collectively BTEX), and other volatile organic compounds were reported in samples from beneath the site. The area of greatest impact was in the vicinity of the dispenser islands (International Technology Corporation (IT), Underground Storage Tank Closure Report, April 1991]. BP subsequently submitted an unauthorized release report to SJCEHD in July 1989 (IT, INTERIM ASSESSMENT REPORT, dated December 5, 1991). On April 26 and 27, 1990, IT oversaw the installation of four groundwater monitoring wells (MW-1 through MW-4) at the site. The wells were installed at 30 feet bgs. With the exception of minor concentrations of benzene and ethylbenzene in a 20-foot sample from boring MW-3, soil samples did not contain detectable concentrations of petroleum hydrocarbons. Groundwater samples from wells MW-1 and MW-3 contained maximum concentrations of total petroleum hydrocarbons as gasoline (TPHg) and benzene at 0.20 parts per million (ppm) and 0.033 ppm, respectively. The direction of groundwater flow was established toward the northeast (IT, Site Assessment Report dated June 1990). In February and March 1991, IT oversaw the removal of two 10,000-gallon unleaded gasoline USTs, one 10,000-gallon leaded gasoline UST, three 3,000-gallon motor oil USTs, and one 3,000- gallon used-oil UST, associated piping, and the installation of replacement USTs in a new excavation as part of the renovation of the facility. The former USTs were of single-walled construction. These replacement USTs are currently in use at the site. The excavated USTs were in good condition, with the exception of some corrosion noted on the oil USTs. TPHg and benzene were detected at concentrations up to 3,500 milligrams per kilogram (mg/kg) and 3.6 mg/kg, respectively, in samples from the former fuel UST excavation. The highest concentrations of petroleum hydrocarbons were detected along the southwestern portion of the former fuel UST excavation. TPHg and benzene were also present in soil from the product piping excavations at maximum respective concentrations of 677 mg/kg and 2.4 mg/kg. With the exception of a concentration of total petroleum hydrocarbons as diesel (TPHd; 29 mg/kg), petroleum hydrocarbons were not detected in soil from the fuel oil UST excavation. Soil from the new excavation also did 11192 CPT Investigation WP 3-2011.doc