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ENSR I approximately 20 feet The schedule was initially set to cycle each point 18 times per day for nine minutes Per point per cycle, followed by an eight minute rest period between cycles The system was shut down in December 2005 due to the indication that site contaminants may have reached asymptotic levels and the System was not effective in reducing the contaminants further Given that the evidence, as demonstrated by graphs included in Appendix D, indicates that the ozone sparge system has not been operating as efficiently as intended, a re-evaluation of technical feasibility and Potential system effectiveness is necessary This re-evaluation should be performed in a phased fashion The first phase will involve collecting some new baseline data and performance testing the sparge system to determine whether it is adequately raising oxygen concentrations in the aquifer New baseline data would include groundwater mounding, pressure, flow and oxygen delivery with distance from the sparge wells, dissolved oxygen, and oxidation-reduction potential (ORP) measurements, and the testing for the presence of naturally occurring hydrocarbon degraders These data would be obtained at a non-impacted upgradient well (i e , MW-8)and the impacted wells (i e , MW-2, MW-10, MW-11, and MW-17) Performance testing should be conducted over a 3-month period with field chemistry parameters ' measured at least monthly The second phase of the remediation evaluation will depend on the results of the first phase If the baseline data suggests that ozone sparging is a viable alternative, then consideration should be given to adding ' additional sparge points within the area of MW-2, MW-10 and MW-11, and upgrading the system components (e g , using larger piping and compressors to deliver more air)as wells as larger(or multiple) ozone generators However, if the results of the performance test indicate that raising oxygen levels in the aquifer is not feasible with the given system,the next phase will be to evaluate alternative technologies (i e , air sparging, in-situ enhanced bioremediation, chemical oxidation)for the source area This newer approach would then be performance tested in the same fashion (less the collection of baseline data) Depending on the flow rates selected, it may be necessary to operate the existing vent wells to control the migration of vapor-phase VOCs that could be volatilized by a higher sparging rate The upgraded system testing would initially be performed without ozone addition to evaluate whether traditional sparging is sufficient to create the more oxygenated conditions that are expected to enhance biodegradation of ' hydrocarbons in the plume After one year of operations, the system operational parameters (e g , dissolved oxygen concentrations, subsurface pressure response, etc )would be reviewed to determine whether further modifications to the system are necessary 5-2 �I l 25 .10"0