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6 <br /> 3.5 Data Analysis <br /> Geomatrix calculated in situ carbohydrate utilization rates (k) using the method <br /> described by Schroth, et all This method is based on the following equation: <br /> In[Cr(t)/Cbr(t)l= b — k(t) <br /> Where : <br /> Cr = the concentration of the reactive solute <br /> Cbr= concentration of the conservative tracer, bromide <br /> t = time <br /> b =axis intercept <br /> As shown on Figure A.2-3, application of this method results in estimated carbohydrate <br /> utilization rates. The results for M-1A are 0.035 per day (half-life of 20 days) and the <br /> results for M-113 are 0.03 per day (half-life of 23 days). Results for well M-1A follow a <br /> linear trend, supporting the assumption that the reaction is a first-order process. Results <br /> for well M-1 B also generally follow a linear trend, except for two samples collected at the <br /> end of the test at approximately 22 and 29 days after injection. <br /> 4 CONCLUSIONS AND CONSIDERATIONS <br /> The purpose of this study was to: (1) identify an area for implementing the ISB remedy; <br /> and, (2) collect information to facilitate the development a pilot test program for the ISB <br /> technology. This information was collected by conducting a treatment zone delineation <br /> effort using CPT and depth-discrete groundwater sampling and aquifer testing to assess <br /> groundwater flow velocity, carbohydrate utilization rates, and effects to water quality due <br /> to carbohydrate addition. <br /> 4.1 Conclusions <br /> The data collected during this study indicates the following: <br /> 1. Transformation of TCE to cis-1,2-DCE in groundwater samples from well M-1A <br /> did not change appreciably during this test. This is possibly due to the higher <br /> groundwater velocity estimated at this location. <br /> 2. Transformation of TCE to cis-1,2-DCE was observed during the M-113 PPT, <br /> indicating limited reductive dechlorination occurred. <br /> 3. Increases in dissolved selenium and arsenic in groundwater were observed <br /> above background levels, with concentrations returning to background levels <br /> after 30 to 99 days, depending on proximity to the injection point. These <br /> increases in concentration to above-MCL levels in groundwater are a significant <br /> concern for any in-situ reductive dehalogenation treatment option, given the <br /> presence of drinking water wells in the Ripon Study Area. <br /> 4. Carbohydrate utilization half-lives of approximately 20 days were observed over <br /> a 30-day period. <br /> 5. The transformation of TCE to cis-1,2-DCE was observed; however breakdown of <br /> TCE to ethene was not observed during the test at either injection location. <br />