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i\ • Corrective Action Plan—Tosco(76)Service Station No 11142, Stockton, California March 13,2002 CONCLUSION Although this may be a feasible technology for this site, more cost effective technology is available OPTION#4 - VAPOR EXTRACTION WITH AIR SPARGING COST Medium to high TIME FRAME Medium to long term due to low hydrocarbon extraction rate ADVANTAGES 1) Can remediate capillary fringe soils 2) Can reduce dissolved concentrations in ground water DISADVANTAGES 1) Ineffective in fine grained soils such as silts and clays encountered at the site 2) Disruption of station activities in order to install wells and piping 3) Construction and operation costs for a extraction system would be high CONCLUSION SECOR performed a 5-day dual-phase extraction test at the site in December of 2001 Although a large vapor radius of influence was • observed (36 to 60 feet) during the test, very low mass removal was reported (6 64 lbs of MtBE) SECOR concluded that DPE is not an effective technology for this site Not a suitable approach for this site, more appropriate methods are available OPTION #S —OZONE MICROSPARGING Ozone microsparging is a process where ozone in air is introduced into the groundwater through specially designed spargers to create small "microbubbles " As these microbubbles rise within the column of water, the dissolved VOCs are rapidly oxidized Low total flow rates (2-6 cfm) are used Any ozone not consumed in the direct reaction with hydrocarbons rapidly decomposes to oxygen This has an added benefit of stimulating the natural biological degradation COST Medium TIME FRAME Short term for impacts on and near the site, longer for offsite impacts ADVANTAGES 1) Relatively low equipment and operating costs 2) Because of low flow rates, vapor extraction to capture off gassing is not required 3) Natural biodegradation rates may be enhanced by introduction of oxygen 140245 08 10