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Former Texaco,Lodi <br /> Page 3 <br /> Dissolved benzene concentrations measured onsite and downgradient have been <br /> consistently low to "non-detect."" The maximum ever measured in any monitoring <br /> well was 120 ppb, which in and of itself indicates "low risk" given the 2,000 ft <br /> upgradient distance to the nearest well. Recurring, "non-detect"" levels in all <br /> monitoring wells indicate low residual risk. <br /> Reported historic trends ofmarginal to "non-detect" BTEX concentrations:further <br /> indicate:that residual petroleum deposits in subsurface sail are.=t'leaching <br /> significant.(if even detectable} concentrations into underlyingi groundwater.. <br /> Reliance by.Regional guard staff cin a theoretical leaching model tosuggest <br /> detectable leachate generation from residual fuel hydioc 6A const!tuents iftsoilg <br /> through-.surface infiltrationand percolation(the site ha&been paved for nearly two <br /> t t iedempirical.data established a! <br /> decadeois:fnt.inconsistent with verified,i , I oversever Years <br /> -of expensive monitoring and analysis, <br /> There lsne substantial evidence in the record to indicate that f6tiner:.releases at the <br /> Togo's sitecontributed,..Pr would be expected to contribute;:tpdetectable <br /> an cross-gradient,o <br /> concentra on o diehl e in groundwater up., own-.. d f <br /> the site:{which through no fault of its own lies within a morepervasive chlorinated, <br /> solvents plume}. its fate:,and.transport properties (e:ghighervidbility'in <br /> particles t I <br /> groundwater than benzene and less tendency to adsorb to esAhAA <br /> benzene) it is likely that over the decades dichloroethane (if any had originated. <br /> onsite) would have,dispersed in groundwater long ago. Given the fact that <br /> dichloroethane is,more mobile and is much less likely to adsorb to soil and that at <br /> least 20 years have elapsed since any leakage might have occurred, it is unlikely <br /> that detectable concentrations of dichloroethane would continue to exist in the <br /> .subsurface even if somer.may have originated at,the site, <br /> Thus,a further search for detectable-concentrations of dichloroethane in soil (or <br /> groundwater) beneath the Togo's site offers little water quality benefit. Further <br /> investigation may reduce "uncertainty" over whether(1) dichloroethane was <br /> present at sufficient proportion in the particular fuels which may have leaked at <br /> this site during its 50 year operational history through 1977, (2) detectable residual <br /> concentrations have remained for at least 20-plus years despite high mobility, and <br /> (3)that a sufficient adsorbed mass of"immobile" dichloroethane has nevertheless <br /> continued for two decades to add measurably to the widespread chlorinated <br /> solvents plume emanating from upgradient sources,. <br /> In.,my opinion, the evidence accepted by the County that dichloroethane is a <br /> predicted andwidespread component of the solvents.plume overwhelms any <br /> Fa Recycled Paper Ouk mission is to pwes¢rve rtnrf enhnncn tfee quality of <br /> Tit ,ensure:their proper:allocalion.an :0 dent use the benefit 00resenOn.fiu <br /> ­ �� � d & , d tumgenerations. <br />