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29 April 2005 f AGE-NC'Project No: 98-0440 Page 6 of 18I ' . T he di sal ved con taminant plume hasmi rated toward nd the northwest fro :th•' forrlen U Tsawa .towards-the property.of the Hay-Grower s.A•ssoclation truck scale and,doinestic well DW-5055 . (Figures Tand 8).-Data further suggests the dissolved contaminant plume maybe migrating:along a .'. discontinuous sand-body occurring at-the top of the water table,or.10"to.13'feet bsg.The location and; distribution of the sand body is depicted on Figures 7 and 8.- Tlie lateral and vertical extent of impacted soil has been defined, the lateral and vertical extent of impacted ground water has also been defined. •4.1.' HYDROCARBON-IMPACTED SOIL Between July 1998 and March 2004,soil sampling was performed at seven soil-boring's(B 1 through B7) and twelve groundwater monitoring Well pilot borings (MW-1 through MW-12) as part'of a subsurface petroleum hydroearbori investigation'. Petroleum hydrocarbons(TPH-g) were"detected in soil samples collected from borings BI through ' B7 and MW-1-through MW-6,-.delineating the maximum potential lateral extent of impacted soil. The vertical.extent of-TPH-g'was delineated by the soil boring samples. Low concentrations of C BTEX were detected in the majority of the same soil borhigs..The most significant concentrations :of BTEX compound were detected in soil samples collected at depths-of 15 feet bsg in borings B 1, B2 and MW-2.. " The plume of impacted soil at the'site has'an estimated northeast-southwest dimension of 155 feet' "Nand northwest-southeast'dimension of 90'feet, :at the former'''UST release area..Mass.voleime calculations-indicate that there.-is approxilnatel'y 651 kg.or 229=gallons of petroleuni..hydrocarbons :.' adsorbedIn the soil•beneath'the site. A endix C . Adsorbed:,soil'is de depicted in lane view in, p _Figure 9. _ 4.2. HYDROCARBON-IMPACTED GROUND WATER ; = Between July 1998 and March 2005,twenty-five ground water monitoring events were performeds. at the.site to monitor dissolved petroleum hydrocarbon concentrations in ground water and to . . characterize ground water flow direction and gradient on the site.Generally,TPH-g and TPH-d were detected.in water samples collected from wells MW-2,MW-5 and MW-6 at concentrations as high as A 1,000 } gll and 3,600 µg11; BTEX compounds from wells-MW-2 MW-5' and MW-6 at . concentrations.as.high: 1,200 ,µg/1 (benzene), 52 gll (toluene), 450 pg/1(ethylbenzene),and - 1,300 µPQ (toluene). Advanced GeoEnvironmental.Inc.