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3 <br /> The addition of carbohydrate to groundwater results in a variety of microbiologically- <br /> mediated chemical reactions that affect dehalo-respiration, consume carbohydrate, and <br /> result in changes to the water quality in the remediation area. The importance of these <br /> reactions in terms of how much carbohydrate is consumed, how fast it is consumed, and <br /> the extent of the reduction of VOCs occurs by dehalo-respiration, is dependent on the <br /> following site-specific conditions: <br /> 1. Carbohydrate concentrations: Carbohydrates must be present at levels higher <br /> than the amount required to reduce the entire mass of naturally occurring nitrate <br /> and sulfate in groundwater. <br /> 2. The rate of groundwater flow into the treatment zone: Electron acceptors, such <br /> as nitrate and sulfate, are present in groundwater and constantly flowing into the <br /> treatment zone. Carbohydrate must be added at a rate that exceeds the rate of <br /> nitrate and sulfate mass loading to the treatment zone. <br /> 3. The mineralogy of aquifer solids (primarily the iron and manganese content of <br /> treatment zone soils): Subsurface bacteria can utilize organic matter and/or <br /> dissolved hydrogen to reduce the ferric iron generally present as various solid <br /> mineral phases within the aquifer sediments5, 6. This process can cause an <br /> increase in dissolved iron and manganese concentrations, can result in the <br /> unintended loss of carbohydrate (to processes other than the intended dehalo- <br /> respiration), and can release arsenic species associated with the aquifer <br /> sediments into groundwater. Monitoring water quality during carbohydrate <br /> amendment to assess the extent and persistence of this process is important to <br /> mitigate potentially adverse effects outside of the treatment zone. <br /> 4. Nutrient availability: Nitrogen and phosphorus are required for cell function and <br /> growth 7. Bacteria capable of transforming chlorinated VOCs to non-toxic <br /> substances also have been shown to require Vitamin B12, which the bacteria <br /> cannot synthesize themselves$. Therefore, if Vitamin B12 is unavailable in the <br /> aquifer system, it must be added to sustain chlorinated VOC reduction in situ. <br /> One readily available source for Vitamin B12 is yeast extract. <br /> 2 CARBOHYDRATE INJECTION PROGRAM <br /> Geomatrix conducted PPTs in B-zone monitoring well M-1 B and A-zone monitoring well <br /> M-1A simultaneously over a 30-day evaluation period9 (see Figure A.2-2). On October <br /> 3, 2005, carbohydrate solution (composed of molasses) and a conservative tracer <br /> (bromide) were injected into the wells. Ten extraction and sampling events were <br /> subsequently completed, the last of which occurred on November 2, 2005. <br /> Extraction well EW-1, located in the vicinity of the test wells, was not operated during the <br /> tests to reduce the potential hydraulic effect of pumping from this well. As requested by <br /> the RWQCB, a representative sample of the injection solution (4.5 grams per liter [g/L] <br /> molasses, 155 milligrams per liter [mg/L] bromide) was analyzed for metals in <br /> accordance with appropriate Environmental protection Agency (EPA) methods. The <br /> results, compared with EPA maximum contaminant levels (MCLs), are presented in <br /> Table A-2.2. <br /> Based on visual lithologic descriptions of test wells, intervals that appeared to be the <br /> most transmissive were targeted for injection. The targeted unit in well M-1A was a <br /> gravelly sand located at 109 to 117 feet below ground surface (bgs). In well M-113, the <br /> target interval was coarse-grained sand from approximately 30 to 37 feet bgs. <br /> Geomatrix installed two inflatable straddle packers in well M-1A at 109 feet bgs to isolate <br />