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�s -_: HISTORY OF SITE WORK Initial UST Removal,Overezcavation,and Sampling Activities On April 21, 1993, two, 10,000-gallon capacity, leaded gasoline underground storage tanks and j one, 5,000-gallon capacity, diesel underground storage tank (USTs) were removed from the subject site. Evax Technologies, Inc. inspected the tanks and collected soil samples from beneath the ends of each leaded gasoline UST, and one sample from beneath the fill end of the diesel UST immediately subsequent to removal. All samples were retrieved from the floor of the excavation at 13.5 feet below surface grade(bsg). Additionally,two soil samples were collected from the soil stockpile flanking the excavation. The stockpile was moved to the south end of the property. Analytical results of the soil les revealed that elevated levels of Total Petroleum Yh samples Hydrocarbons as gasoline (TPH-g); Total Extractable Petroleum Hydrocarbons as diesel (TEPH- = d); volatile aromatics benzene, toluene, ethylbenzene, xylenes (BTEC, and lead were present in the samples collected from the excavation and from the stockpile. The overexcavation of the former tank pit was undertaken on July 16, 1993 by W.W. Irwin, Inc.. The work was periodically supervised by Mr. Nfichael Collins, VCPHS EHD Registered Environmental Health Specialist. As the excavation proceeded, soil samples were collected for lithologic analysis and organic vapor analysis (OVA) meter readings were taken in order to direct the excavation.. The excavation was expanded slightly in all directions from the original tank pit to an area approximately 35 square feet and to a depth of approximately 18 to 20 feet below surface grade (bsg). The excavation was halted when the excavator reached the limits of its extension and the northern wall became inaccessible. Groundwater was not encountered. 3 An estimated 260 cubic yards of excavated soil was removed from the tank pit and stored at a location on the south side of the property, and separately from soil stockpiled during the tank }=- removal operation. The excavation was backfilled in May of 1994 subsequent to collection of stockpile soil samples for single-sample-composite analyses. Backfilling was approved in a letter dated May 10, 1994 from Specialist Collins to Mr. Dwight Davis of the Pegasus Group. Hydropunch'rm Sampling On April 8, 1994, three HydropunchTM boreholes (HP-1, HP-2, and HP-3 depicted on Figures 2 and 3)were drilled near the north, east, and west flanks of the overexcavation. Groundwater was encountered at an average depth of 23.7 feet below surface grade(bsg). The groundwater sample collected and analyzed from HP-3 revealed benzene at 160 micrograms per liter (µg11), prompting the SJCPHS EHD to order the completion of three monitoring wells for groundwater direction and gradient determination, and possible definition of the contaminant migratory path. HORIZON ENVIRONMENTAL,INC. 2 PROJECT NO.2005.41 j' JULY 1996 I l