ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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amec- • An increase in dissolved metals (iron, manganese and arsenic). Ferric iron and manganese oxides can be reduced to soluble, divalent forms, resulting in an increase in dissolved iron and manganese concentrations. An increase in arsenic concentrations can also occur in conjunction with this process. These effects were demonstrated to be a concern during pilot testing conducted at the site by Geomatrix in 2006 (Geomatrix, 2006), where arsenic concentrations increased to more than 10 times the acceptable level in drinking water due to carbohydrate injection as a substrate for bioremediation (it is important to note that these effects were very localized during the 2006 pilot testing because only a small amount of carbohydrate was added to the aquifer system with the intention of evaluating potential side-effects on groundwater chemistry). • An increase in alkalinity. Fermentation of carbohydrate results in the production of volatile fatty acids and bicarbonate, both of which affect alkalinity. Alkalinity typically increases as organic carbon substrates are biodegraded. • An increase in dissolved methane. Methane production typically occurs after sulfate and other electron acceptors have been depleted, and an excess of total organic carbon has been established. • A decrease in oxidation-reduction potential (ORP) and pH. ORP is reduced due to anaerobic conditions; pH is reduced due to fermentation resulting in acetate and organic acids. 2.3 TRANSPORT PROCESSES The ability to deliver or disperse injected microbes throughout the pore volume of the target treatment zone is of primary importance to the effectiveness of bioaugmentation. There are two physical processes that will affect the ability to deliver microbes within porous media such as sand and gravel aquifers: • Mechanical filtration (straining)where bacteria are larger than the pore spaces of aquifer sediments, and • Attachment of microbes to the surface of aquifer sediments. Mechanical filtration occurs when bacteria are trapped in pore throats through which they are traveling. Recent studies have indicated that straining occurs at lower particle diameter to bacteria diameter ratios, to values as low as 0.2% (Bradford et al., 2002; Bradford et al., 2004). Given that typical microbes are approximately —2 pm in size, this suggest that mechanical filtration can occur even in poorly graded medium sand (grain size, 250-500 pm; Freeze and Cherry, 1979), and more filtration is anticipated for silty sand and gravel, where the finer-grained silt fraction controls the minimum size of pore throats. Therefore, even in the relatively coarse-grained sediments of the Intermediate Aquifer, mechanical filtration by the AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTFS Assessment_Apx B_01 2711\Attachment B.2\Attach B-2.doc 132-3