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............. 22 SR-9, MAMM , galml, mmwg, Blaine Tech Inc.was also onsite 26 February 1988 to observe the additional excavation of sods in anti around the tank field. Blaine sampled the stockpiles resulting from the excavation, Sample#1 contained 55 ppm high boiling point hydrocarbons.340 ppm low- boiling point hydrocobons,28 ppm toluicnc,26 ppm xylenes,and 1.2 ppm ethylbemcne. A composite sample.2A and 2B,contalned 490 ppm low boiling point hydrocarbons. Blaine Tech's report Is stretched as Appendix F. 2.2 INSTALLA71ON OPMONITOMG WELLS The occurrence of petroleum hydrocarbons at the tank ficid warraintrA the insWiation or six ground-water monitoring wells. The wells were insmUed between 7 and 11 November 1988 by EA Enginoulng.Science,and'rechnology,Inc.and Specuum Exploration Ine. The locations of the six wells am indicated on Fig=6. Based on information from the San Joaquin County Flood Control District's semiannual report on ground water,ground water was expected to flow to the east toward El Dorado Street;the mo staring wells%,cit therefore laid out&ndcipadng transport of petroleum hydrocaftni with the griound water to the cast. The soil borings were drilled to depths between 41 and 50 feet with jui Acker notary drill using 10 Inch outside-dim ter.hollow-stem auger. The driU was contracted from Spectrum Exploration Inc.(C57 license number 512268). Water was first encountered in the borings between 36 and 43 fest. By 15 November 1988.the depth to ground water had decreased to stadc levels bcm=36 and 37 feet below the ground surface.. In order to limit the extent of vertical migration contaminants-03 the monitoring wells,the$03 borings were terminated in a layer of competent clay that underlies:he main water-producing Sands. The borings were completed as mnitoring wells by installing nominal 4-inch Schedule 40 PVC casing. Screened casing with 0.020 inch slots was Installed to dcpths that provide I& VVXt am 10 feet of su=above the stadc water level identified during drilling and suffident section below to rtpm=t the shallowest water table. The screcned;-I-rv3js were and packed,%ith Uacuu#VI2 sand fmm below the bottom of the=t_ sp to depths more than 2 fed above the top of screen to provide an effective filterpack and MVM the bentonite and pvjt"fix=ocdu&j;the xmm The fdtff pack was scaled with bendoalte pdkiL A neat c=nt grow zeal Was pumped into die n=taldng&=W space above a berms Wtc"with the&M jig's mud p=p and a 25 fm long ho= The well tops were cotnpkwd with water-tight uaffic boxes set in oon=tc which require a