ARCHIVED REPORTS XR0006513 - Laserfiche WebLink

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1 *Sample results obtained on 12/16/1997 were not included in the averagc results situ;those samples were cross contanunated with suhrucisible pump operattow; MW 12 is located off site, down gradient of MW8 Attenuation of dissolved TPH-g, benzene and MTBE concentrations in MW 12 are not consistent with attenuation identified in MW2, MW3, 1ViW8, and MW 13 all of which intersect the potential migration pathway from the UST area of the site to MW 12 This supports that dissolved petroleum compounds observed in MW 12 have ' originated from an off site source Average yearly benzene concentrations continue to decrease approximately linearly from 1993 to present Yearly Average Benzene and TPH-g Concentrations from NLW12 Year Average benzene concentration(Eig/L) Average TPH-G concentration(kigIL) 1992 <93> <510> 1993 <515> <1,622> ' 1994 <168> <950> 1995 <115> <2,622> ' 1996 <150> <6,475> 1997* <69> <6,870> 1998 <15> <6 970> ' *Sample results obtained on 12/16/1997 were not included in the.average results since those samples were cross contaminated with submersible pump operations MW l 3 intersects the pathway of migration east of the UST area of the site Dissolved TPH-g has attenuated 99% since installation in 1997 Dissolved Benzene has attenuated greater than 99%, from 15 to <0 5 ,u since installation to 1997 Yearly Average Benzene and TPH-g Concentrations from NIW13 Year Average benzene concentration(MgIL) Average TPH-G concentration(pg/L) 1997 NA NA 1998 <3900> <8> NOTE MTBE has identified, exclusively, in the offsite wells MWS, MW11 and MW12 in monitonng performed in January 1999 using EPA Method 8260 This exclusive off site identification of MTBE on the Krdgen Auto property and not in the groundwater underlying this site, supports that the source of MTBE is off site, with concentrations below 45 ug/L 14