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1 05-0,-200V Ge"oly, LLC- dro eof is investigation fcw Nunap page(3 e r V d <br /> Greundwate,z Grab Sample Results and TCLP Analysis for- B-7) identified in the grab <br /> sample from 96.4 feet bgs was collected from residual groundwater trapped in the <br /> open borehole after the augers had smeared off the perched aquifer as was <br /> 1 evident during the recent year 2001 excavation of MW-1. In light of this correlation, <br /> the dissolved hydrocarbon contamination cannot even be considered a low <br /> estimate of hydrocarbons in groundwater as the likelihood of cross-contamination <br /> from shallower soils encountered <br /> encountered during drilling was very high. <br /> L...�L'1Ck�gm"rY w�' anyi1CV. -OR 1321U6.GGm <br /> 1 Soil testing results from soil samples collected in 1998 from deep soil boring 0-7 <br /> demonstrate that benzene is not leachable from soil,where it can reach <br /> groundwater,from approximately 60 feet bgs to the perched groundwater zone <br /> located at approximately 82 feet bgs. Soil sample 7-617 collected from 59-59 1/2 fee4 <br /> bgs revealed 0.011 ppm benzene in soil yet the leachate from this sample yielded <br /> !ND (ppb) levels of benzene. <br /> It is clear that benzene at this site is not leachable to groundwater as <br /> demonstrated by the fact that there was no benzene was identified in soil above <br /> the aquifer which could impact the groundwater as demonstrated by the following <br /> trends for benzene identified in soil in ppm: <br /> B-7 - 900CYGMEng 00VOID{700 09 40 591/2 OZW �DZO - CSD Q 62 SQW CDZS <br /> MW-1 - [SID from 38 to M fco4 c <br /> MW-2 - ND 811 feet bgp <br /> MW-3 - Dear inn treancD mom M w Oalh QG\-_4 [tea - MD t1rrom 4SI/2 40 X36 q= 02�gv <br /> Furthermore, the TCLP test on soil samples collected from soil boring B-7 in 1998 <br /> from 591/2 to 841/2 demonstrated that benzene is not leachable form soot 4o the <br /> groundwater. <br /> (See Agure 2 for 9000£3 SGC960rm Danzo no 4Qdp irGOUG20 In PPlb) <br /> (See Vable 011 for 4CLP Benzeno EoachabOQ Brom SaH) <br /> (Sec: Appendix E for Laborrecoaq Do= ShaGgo ftP Grab Swv pOo 2csm0w <br /> andl 7CLP Analysl5 for 8-7) <br /> ATTENUATION of BENZENE IN THE VADOSE ZONE <br /> The vertical attenuation of residual benzene in soil (e.g. 13 ppm benzene identified <br /> at approximately 40 feet bgs) as it migrates vertically downwards towards the <br /> perched groundwater (i.e. at a depth of 80 feet bgs) was calculated utilizing a finite <br /> source model scenario (Graphical Approach for Determining Site-Specific <br /> Dilution-Attenuation Factors (DAFs) User's Guide & Vechnical Background <br /> ®ocumenu,APO [PUBLMAMOOM {CUMBER,%5T), (PERRUARV 1998). <br /> According to TCLP analysis, 460 ppb benzene was leachable from the 13 ppm <br /> benzene in the soil at approximately 40 feet bgs. According to the model, based <br /> upon available site specific parameters, dilution through vertical attenuation in the <br /> vadose zone,would diminish to the following concentrations with depth: <br /> QEPTH IN BGS FEET BGS ATTENUATED BENZENE CONCENTRATION IN PPB <br />' 50 0.293 <br /> 70 0.086 <br /> 84 (PERCHED OROUNOWATER) 0.037 <br /> 05-03-20ot Iv, LLC- Hydrogeoiogie twestigation for Nunan Page 6 of 10 <br />