ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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• IAS does not result in a uniform distribution of air bubbles around the injection point, but rather in a limited number of discrete air channels that are heterogeneously distributed and difficult to control. • There is a small mass transfer zone in the immediate vicinity of the air channels where dissolved oxygen concentrations are greatest. • The delivery of oxygen to water saturated zones located between the air channels is limited by diffusion (a slow process). Because aerobic degradation rates for biosparging applications are dependent on oxygen delivery, contaminant removal rates are highest adjacent to and near the air channels. For enhanced rates of aerobic biodegradation to occur outside the immediate vicinity of the air channels, oxygen must diffuse into the saturated zones located between the air channels (a slow process). The rate at which the saturated zones between the air channels can be supplied with oxygen can become the limiting process for aerobic biodegradation (Braids and Ong, 2001; Johnson, 1998). It would also be very difficult to maintain aerobic conditions in groundwater near the WWTP based on the highly reducing groundwater conditions in this area as discussed in Technical Attachment B.4. These delivery issues are important considerations for the design of biosparge systems discussed in Section 2.3. 2.2 TREATMENT PROCESSES With the exception of vinyl chloride (VC), chlorinated ethenes (i.e. tetrachloroethylene [PCE], trichloroethylene [TCE], cis-1,2-dichloroethylene [cDCE]) are not readily degradable by direct aerobic oxidation reactions. Some studies have indicated cDCE can be degraded aerobically. TCE and PCE have not been shown to be degraded aerobically (EPA, 1998; ITRC 1998; EPA, 2000). A variation of aerobically based biosparging applications is aerobic cometabolism where an electron donor such as toluene, phenol, methane, or propane is co-injected with oxygen (the electron acceptor). Bacteria produce non-specific oxygenase enzymes to metabolize the injected substrate (e.g. toluene). The production of oxygenase enzymes can facilitate oxidation of TCE, cDCE, and VC. These oxidation reactions are considered fortuitous with the microbes deriving no net benefit from the oxidation of chlorinated ethenes (EPA, 1998; ITRC 1998; EPA, 2000). Research conducted in the 1980s and 1990s indicated chlorinated ethenes (with the exception of PCE) were degradable cometabolically (Wilson and Wilson, 1985; Semprini et al., 1990; Munkatta-Marr et al., 1997; Bradley at al., 1998; McCarty et al., 1998). Field implementation of AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.1\Attach B1.doc 131-3