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0 <br /> LFR Inc. <br /> Ethane and Ethene. Ethane and ethene are both by-products of reductive <br /> dechlorination. The presence of these compounds within a plume is a strong indicator <br /> of reductive dechlorination processes and that complete reductive dechlorination is <br /> occurring. In other words, the presence of ethane and ethene indicates that reductive <br /> dechlorination is not stagnating at cis-1,2-DCE or vinyl chloride. <br /> As shown in Table 3, ethane and ethene concentrations were detected at the highest <br /> concentrations in groundwater from B-zone wells MW-205B (ethane: 3.8 µg/1 and <br /> ethene: 0.28 µg/1) and MW-020B (ethane: 0.161Ag/1 and ethene: 0.12 µg/1). Ethane was <br /> not detected in wells MW-108A and MW-208B (<0.025 µg/1), located in the proposed <br /> ERD treatment zone and downgradient. Ethene was detected in wells MW-108A and <br /> MW-208B at concentrations of 0.029 µg/l and 0.038 µg/1, respectively. The presence <br /> of ethane and ethene within the three B-zone wells indicates that active and complete <br /> anaerobic reductive dechlorination is occurring. However, the absence of ethane and <br /> the minor detection of ethene in A-zone well MW-108A, in the proposed ERD <br /> treatment zone, provides evidence that anaerobic activity may be present but is not as <br /> active as within the B zone and can likely be enhanced by ERD injection. <br /> Hydrogen. The presence of hydrogen concentrations is also an indicator of anaerobic <br /> activity. Hydrogen concentrations ranged from 0.950 to 1.6 nanoMolars (W). The <br /> highest hydrogen concentration was found at upgradient B-zone well MW-020B (1.60 <br /> DNI), which may be attributable to natural reductive dechlorination occurring in the <br /> historical source zone. The hydrogen results can be used to help determine which <br /> electron acceptor(s) are active within an anaerobic environment. The hydrogen results <br /> indicate that sulfate-reducing conditions may exist in the proposed ERD treatment zone <br /> and downgradient in the A zone and B zone. <br /> 3.2.3 Field-Measured Geochemical Results <br /> Results of field-measured geochemical parameters are summarized in Table 4. General <br /> water-quality parameters (temperature, pH, and specific conductivity), which are used <br /> to monitor stabilization of parameters in groundwater during purging to ensure that a <br /> representative groundwater sample is collected, are included in Table 4. <br /> Oxidation-Reduction Potential. Low or negative ORP values are indicative of a <br /> reductive environment. ORP measurements ranged from -97.3 milliVolts (mV) in <br /> A-zone well MW-108A to -134.7 mV in B-zone well MW-020B. The ORP results in <br /> the three B-zone wells indicate a strongly reducing environment. The ORP result in the <br /> A-zone well indicates a less reducing environmental. <br /> Dissolved Oxygen. Low DO concentrations are a good indicator of anaerobic conditions <br /> favorable for natural attenuation of PCE. The DO measurements shown in Table 4 were <br /> obtained by using a DO meter in a flow-through cell. In the three B-zone wells, the DO <br /> results were less than 1 mg/1. DO concentrations that are less than 1 mg/1 are indicative <br /> of reductive conditions that are more favorable for natural attenuation. DO <br /> concentrations in A-zone well MW-108A had a DO of 2.16 mg/1, in the immediately <br /> Page 12 wp-PhV_IRA-Sep07+i=1-06750.dmJfr <br />