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CLEARWATER ' C R O U P Environmental Servrces placed in excavation backfill or in wells and borings, and releases oxygen to naturally occurring ' microbes as it is hydrated Thus, the need for controls and the expense related to weekly or daily maintenance is precluded Theoretically, the additional oxygen provided by ORC stimulates ' aerobic microbial growth and activity The ease of use and low maintenance have elevated ORC's status to that of an industry standard However, interviews with chemists specializing in ' hydrocarbon degrading microbes in groundwater suggest that ORC may not be such a good idea Once oxygen is released, the by-product of magnesium peroxide is magnesium hydroxide, which raises the pH of groundwater and actually restricts the growth or even kills off the desired ' microbes Further, in the presence of carbonate, magnesium hydroxide encourages cementation lowering permeability of the substrate Also the radius of influence of ORC's dissolved oxygen ' diffusion is very limited in low permeability soils such as exist at this site The large quantity of ORC needed (at least 30 lbs for each 1 lb of hydrocarbons) and high cost per pound negate its use as an economical solution ' A relatively new oxygen delivery technology, 1SOC, operates on the same basic principle of providing an oxygen enriched environment for naturally occurring microbes to aerobically degrade hydrocarbons However, it works by supersaturating groundwater with gaseous oxygen ' through monitoring wells and diffusing through the surrounding area with a average radius of 10- to 20-feet Since mass transport laws govern the distribution of oxygen,_ low hydraulic ' transmissivity of soils is not an impediment as with technologies which rely on flow though the formation Case studies have proven effectiveness in soils with low permiability, such as exist at 2. this site Additionally, by utilizing gaseous oxygen,byproducts are not created in the subsurface d ' This technology 1s also desirable as it is effective as a primary remediation technology (both sorbed- and dissolved-phase), requires minimal effort to install, and does not disrupt site ' operations to the extent that other remediation efforts would An iSOC information package is attached as Appendix F Discussions with an iSOC representative regarding the hydrogeology and contaminant mass location at the site suggest a conservative estimated radius of influence of 10 to 12 feet Using these values as a guide it is estimated that a 25 iSOC well system should be sufficient as a primary remedial technology the site (Figure 8), assuming other parameters were favorable If iSOC were used as a polishing measure for residual sorbed-phase after excavation, and to ' ZB 178C CAP 17 November 20,2002