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5. CONCLUSION OF FEASIBILITY STUDY • In order to achieve the remedial goals of continued reduction of hydrocarbon mass in the subsurface and continued control of the downgradient migration of dissolved phase hydrocarbons, and with an understanding that MCLS for groundwater may not be economically or technically attainable in a timely manner with the technology currently available, eleven technologies were screened The screening criteria included (1) reduction of toxicity, mobility, Iand volume, (2) technical feasibility, and (3) cost In-situ oxidation technologies such as the introduction of ozone or modified Fenton's reagent are not considered acceptable because these oxidants have a limited ability to address residual LPH, and heterogeneous soils and site conditions are such that the capacity for uniform distribution of the oxidants throughout the fine-grained materials below groundwater is limited These infection I technologies can also increase the risk of mobilizing hydrocarbons in the downgradient direction by disrupting the equilibrium of hydrocarbons in the saturated zone Enhanced bioremediation, steam stripping, and air sparging have similar limitations SVE, which was implemented at the site in conjunction with AS, was terminated after having reached asymptotic influent df, 1 concentrations SVE alone cannot address hydrocarbon mass below groundwater without c significantly decreasing the groundwater table UVB also implemented at the site showed w/ limited effectiveness UVB and SVE/AS were implemented at the site in an attempt to remediate pd-0 the site without promoting the migration of hydrocarbons from other sitesfp O) .GC''A Excavation is potentially feasible for the removal of a majority of the onsite hydrocarbon mass from 20 to 40 feet bgs Soils at residual saturation beneath Rosemarie Lane and the property north of the site would, however, be left in place Excavating to 40 feet onsite would increase I physical risks and generate public nuisance issues Additionally, the area proposed for excavation would need to be dewatered, which would promote the migration of hydrocarbons and MTBE from the neighboring offsite sources The treatment and disposal of water would be ' significant, and the capacity limits for local sanitary and storm sewers may be a problem Excavation and dewatering efforts would disrupt equilibrium conditions in the subsurface, and potentially cause temporary increases in the mobility of hydrocarbons Additionally, air quality Iissues associated with exposing subsurface hydrocarbons would need to be evaluated DPE accompanied by groundwater extraction to dewater the area of submerged entrapped I hydrocarbons may be feasible with a significant number of extraction wells Removal of hydrocarbon mass would be limited within the fine-grained soil The dewatering associated with DPE would risk mobilization of hydrocarbons and MTBE from offsite sources As discussed above, the capacity limits for local sanitary and storm sewers may be a problem The difficulty in treating submerged, low-permeability soils containing hydrocarbons at residual saturation within close proximity of upgradient and crossgradient potential source areas has historically limited and will continue to greatly limit the applicability of treatment technologies at this site As such, significant limitations exist for all of the evaluated technologies Mass reduction and control of downgradient migration of hydrocarbons has and is currently being achieved by natural attenuation processes As such, monitored natural attenuation is the proposed remedial alternative G\Prgects1739421MASMRIWP\WPO3031WPtx dcl- 21