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r Page 3 i 1 sample collected 10 feet away from the excavation at a depth of 16 feet Based on the positive organic vapor screening results, Nomellini Construction decided to backfill the excavation with clean fill and further assess the extent of the contamination with a soil boring program In May, 1989 Kleinfelder supervised Y p ed the drilling of nine Boll borings (B-1 through B-9) in the ' vicinity of the former tank pit. Samples were analyzed from depths of 10 5 to 26 feet Ten of 15 soil samples contained total petroleum hydrocarbons as gasoline at levels ranging from nondetect to 450 ppm High concentrations of TPH as gasoline (TPH-g}, benzene toluene,uene, ethylbenzene, and xylenes (BTEX) were detected just above and below the groundwater surface in boring B-1 which was located adjacent to the south edge of the excavation Similarly, high TPH-g concentrations were detected just above the groundwater surface in B-2, approximately 20 feet north of the former tank excavation The remaining samples had relatively low concentrations detected, but TPH-g levels were consistently detected just above the groundwater surface Groundwater was encountered at a depth of about 25 feet below ground surface In February, 1991, Kleinfelder drilled three bonngs B-10 through B-12 These borings were subsequently converted into monitor wells MW-1 through MW-3 TPH-g was detected in the E groundwater in February, 1991 in MW-1 through MW-3 at concentrations of 1,700 ppm, 10,000 ppm and 1,500 ppm, respectively In June, 1991, 15 feet of free product was measured in MW- 1 The groundwater gradient has generally varied between the northeast to southeast On March 16, 1992, Artesian Environmental Consultants measured hydrocarbon thickness in MW-1 to be 182 feet Groundwater flow direction on March 16, 1992 was to the southeast Water depth was measured on March 16, 1992 for MW-1 through MW-3 at 32 5, 32 7 and 32 4 ' feet below ground surface, respectively 1 I 100 Shoreline Hwy, Suite 295 B - Mill Valley, CA 94941 • (415)381-6456 FAX (415) 389-0423