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' GEOMATRIX <br /> Alternatives 2, 3,4, and 5, however,the number of uncertainties and necessary assumptions make <br /> ' calculation of a meaningful number impossible Alternative 2 would reduce significant quantities of <br /> TPH over a 10 year period,but the heavier,non-volatile fractions of the petroleum would likely not <br /> ' be remediated using this technology for a significantly longer period of time The variously sized <br /> partial excavations evaluated as Alternatives 3,4, and 5,would be effective to the areas excavated, <br /> ' however groundwater in the remaining non-excavated areas would remain above WQOs for a long <br /> period of time The shoring and dewatenng required for alternatives 4 and 5 cause these alternatives <br /> to not be cost effective Complete excavation of affected soil (Alternatives 6 and 7)would be <br /> economically infeasible at this site due to the extensive shoring and dewatering required and because <br /> a significant amount of the affected soil lies beneath the adjacent property with railroad tracks <br /> ' The contingency for removing mass is to proceed with a limited excavation Alternative 3 removes <br /> g Y g <br /> ' mass through excavation and removal of free product in the excavation This alternative provides <br /> additional mass removal compared to Alternative 1 and is the lowest cost alternative for removing <br /> mass through excavation <br /> 5.0 SUMMARY AND RECOMMENDATIONS <br /> lipResidual petroleum hydrocarbons measured as TPHd and TPHg in shallow groundwater in contact <br /> with the limited residual petroleum in soil will likely remain above WQOs in a very localized volume <br /> ' for a long period of time Nonetheless, during this time, <br /> ' • the constituents will not pose a threat to current or probable future beneficial uses of the <br /> affected water, <br /> will not threaten water supply wells or surface water, <br /> and will not pose a threat to human health <br /> ' Therefore,Geomatnx recommends natural attenuation(with attempted free product removal and a <br /> human health risk evaluation)as the most appropriate remedial option for this site <br /> 60 REFERENCES <br /> ATC Associates,Inc , 1998a, Summary Report of Additional Subsurface Investigation,Continental <br /> Gram, 1805 Harbor Street, Stockton, California,October 19 <br /> ' ATC Associates,Inc , 1998b,Monitoring Report Fourth Quarter 1998,Continental Grain, 1805 <br /> Harbor Street, Stockton,California,December 29 <br /> 1 1Doc_Safe19000s199631CAP1CAP txt doc 9 <br />