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� *r <br /> Woodward-Clyde Corl5ultarrir, <br /> 6.0 REMEDIAL ACTION FLAN <br /> As describad above, the remedial options applicable to the Caltrans Shop 10 facility to <br /> remediate hydrocarbon contaminated soils and groundwater is groundwater extraction with <br /> vapor extraction (VES) and/or enhanced insitu biodegradation of soils with air stripping ~ <br /> treatment of the groundwater. As shown on API Residual Hydrocarbon Concentration <br /> Curves in Appendix D on Figure 5.4, it wiil take at least 30,years of groundwater pumping <br /> to reduce the concentration of benzene and toluene to the EPA's;MCL of 1 ugll and DOHS <br /> action levels of 100 ugli, respectively. Ethylbenzene and total xylenes can be reduced to <br /> acceptable regulatory levels In less that 3 years.L• <br /> To reduce the amount of time required to improve the groundwater quality to DOHS action <br /> levels and EPA MCL's, it is recommended that VIES and/or enhanced insitu biodegradation:of <br /> the soils and groundwater be implemented concurrently with groundwater ey'raction. <br /> Vapor extraction will increase the surface area of subsa <br /> rfa So esoils exposving e tiletoenhancing <br /> organnc9 <br /> insitu biodegradation of soils and groundwater while <br /> ic <br /> chemicals. Insitu biodegradation enhanced o�n� the <br /> biodegradation of both contaminated <br /> added to the groundwater will directly increase <br /> 7 soils and groundwater. The time it will take to co;rplele the remediation, however, is not <br /> known. Bench scale modeling is required to evaluate this time. u ingheither purposes <br /> rerriedf this <br /> cost comparison, it is assumed that cleanup will take 5 y I <br /> strategy described above. <br /> Estimates of capital, and operating and maintenance costs for the installation and long term <br /> maintair.ence of groundwater extraction and either VES or enhanced insitu biodegradation <br /> systems are summarized in Tables 8 and 9, The costs were developed using American <br /> Petroleum Institute's 1987 curves for comparing costs versus treatment oars ns for <br /> hydrocarbon related contaminFtion sites. The curves provide costs in <br /> ich <br /> were increased by 14.4% using Engineering News <br /> The ecord costsCassumelahatost totaldexes 10 <br /> flow of <br /> adjust for inflation and reflect 1990 costs. <br /> contaminated groundwater from the site is 20 gpm from 4 centrally located wells. WCC's <br /> other assumptions are described below. <br /> 1) The size of the groundwater plume is 300 feetdhe thickness e unknown).of <br /> contaminated aquifer Is 10 feet (the actual plume dimensionsar <br /> 26 <br />