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' ENSR � i ' agricultural and other purposes) in which the groundwater in the area had risen approximately 30 feet in some areas January 1988 Preliminary Phase I investigation conducted Five soil borings were installed to a depth of approximately 20 to 25 feet below ground surface (bgs) and 10 sod samples were analyzed for TPH and BTEX Highest levels of hydrocarbons were detected on either side of the pump island Groundwater encountered at approximately 25 to 30 feet bgs February 1988 Service station was demolished and the site was graded and remains vacant March 1988 The two 10,000-gallon gasoline and one 550-gallon USTs were removed Post- excavation samples indicated hydrocarbons still remained in the gasoline tank pit ' area Additional excavation was performed which had expanded the tank cavity to 25 x 35 feet and to an approximate depth of 30 feet Groundwater had entered the tank cavity several hours after the excavation was competed A total of 1,100 cubic yards of soil were removed during excavation ARCADIS report indicates a SJCPHS letter states that 1,350 cubic yards were removed, but later correspondence questions the exact amount of sod excavated June 1988 Three borings were drilled and monitoring wells installed (MW-1 through MW-3) Sod samples indicated that extent of contamination in soil is delineated to the north of the tank cavity, to the west and east of the former pump island The quarterly groundwater sampling program began at this time August 1989 Three additional soil borings were drilled with two monitoring wells installed at the two offsite boring locations (MW-4 and MW-5) Sod analytical results indicate that soil has been delineated at the southern end of the property based on TPHg and BTEX results being below detection limits TPHg was detected in both MW-4 and MW-5 as well as low levels of ethylbenzene in MW-5 and total xylenes in both wells August 1990 Summary of eight quarterly groundwater sampling events (June 1988 through August 1990) show that MW-2 has the highest TPHg and BTEX concentrations and have increased in concentration each monitoring event Wells MW-1 and MW-3 to MW-5 have BTEX below detection limits or low levels TPHg concentrations are detected in MW-3 ranging from 120 to 1,000 ppb TPHg concentrations are also detected in MW-4 and MW-5, ranging from 86 to 150 and 30 to 180 ppb, respectively Soils were delineated, with residual hydrocarbons remaining northwest ' and southeast of the pump island March 1992 Vapor extraction (VE) pilot test performed to collect site-specific data and evaluate VE as a remedial alternative Results of test indicate that, with a wellhead flow rate of ' 43 cubic feet per minute (cfm), an estimated radius of influence of approximately 25 feet could be achieved for one vapor extraction well August 1993 Recommendation to install 2 additional monitoring wells (one south to complete lateral definition [MW-9] and one southwest in an upgradient location [MW-8]) and add to the existing quarterly groundwater sampling program July 1994 Wells MW-8 and MW-9 were installed on July 14, 1994 MW-8 was installed west and upgradient of the site and MW-9 was installed southeast of the site in the street on Pacific Avenue PID readings were zero and soil samples (collected every 10 feet) were all non-detect for TPHg and BTEX Wells were developed and sampled on August 1, 1994 for TPHg and BTEX BTEX in both wells was non-detect TPHg was 93 ppb for MW-8 and 110 ppb for MW-9 2-2