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�- 1 will ultimately depend on the radius of influence and downgradient dispersion ofthe oxygenated water. There may be some uncertainty as to the uniformity of treatment because of the variability in aquifer characteristics and because the efficacy of the process is more difficult to verify. The duration ofthe treatment is very difficult to estimate as the actual mass ofcontaminants(dissolved and residual and/or sorbed phases)and biodegradation rate for a particular contaminant are difficult to predict with any ► accuracy. For the sake of estimation, Alternative 1 will require two to four years to complete. 5.1.2 Implementability Alternative 1 will be difficult to implement because it will likelyrequire multiple events ofinjectingtheORC® with use of a direct-push drill rig. One injection event is anticipated to occur over 20 field days. ► Fortunately,the required drill rig can be operated off ofthe back of a pickup truck or pushcart for easier access. This will eliminate the need to close the streets completely and at most,will only require partially ► blocking one lane of traffic. Access to the sidewalks near source wells MW-2 and MW-2A will also be necessary along with injection locations within the southeast comer ofthe HSA building. Interference with utilities will need to be carefullymonitored due to the fixed intervals ofinjection locations. Ifit becomes ► necessary to relocate injection locations around utilities,or ifaccess inside the HSA building is not possible, the effectiveness of this technology will decrease as access to the source is limited. ► 5.1.3 Cost ` The overall cost ofAltemative 1 is estimated at approximately S 164,890,including purchasing the ORC® for one application,installing the two new wells,injecting the ORC®with the direct-push drill rig,and conducting quarterly groundwater monitoring for the first year. Proposals for subsequent quarterly monitoring will be submitted to Capital Projects annually. The detailed cost breakdown for Alternative 1 is presented in Appendix A, Table A-1. �- 5.2 Alternative 2—Data Gaps Sampling and Low Risk Site Closure WESTON will develop a proposal outlining the procedures necessary to address the current site data gaps, ` which will include the procedures for conducting the vertical extent groundwater investigation and installing the new well in the source area,installing the new downgradient well,redeveloping MW-2,surveying the ` well elevations,and conducting one year of quarterly monitoring. Pending the information discovered during the data gaps sampling effort,WESTON will then proceed with compiling the site information into a low risk closure request during the following year. r 5.2.1 Effectiveness Alternative 2 will be effective in gaining a better understanding ofthe subsurface mechanics ofthe site, which will potentially lead to an expedited site closure leaving the mass of contaminants in place. The ` effectiveness ofAltemative 2 will be ensured by conducting quarterly monitoring for a period ofone year. 18