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Oxidation-Reduction Potential. The ORP of groundwater is a measure of electron activity and is ' an indicator of the relative tendency of a solution to accept or transfer electrons. Oxidation- reduction reactions in groundwater containing organic compounds are usually biologically mediated, and therefore, the ORP of a groundwater system depends upon and influences rates of biodegradation. Reductive dechlorination is generally considered to be possible as long as ORP is below approximately 50 mV, although it is more likely to be significant in a more reducing environment (i.e., ORP of—100 mV or below). ORP measurements at this site were all positive ' with the exception of measurements from MW-4B, MW-713 and MW-813; however over time, these measurements were not consistently below zero at any of these three wells. ' pH. The pH of groundwater has an effect on the presence and vigor of microbial populations in groundwater. This is especially true for methanogens. Microbes capable of degrading chlorinated compounds generally thrive in a pH environment between 6 and 8 standard units. The pH of groundwater samples at the French Camp site vary between approximately 4.0 and 8.8; however, the majority of the samples fall within 6 to 8 standard units, which is within the ' range conducive to reductive dechlorination. 4. Chemical Characterization of the Amendment The proposed amendment to the aquifer consists of injection of zero-valent iron (ZVI) with a guar and an enzyme breaker to assist in the dehalogenation of carbon tetrachloride. Guar gum makes the slurry viscous and allows the granular iron to be suspended and pumped into the injection well. Guar gum is a food additive used to increase the viscosity of products, ' such as cream cheese and ice cream. The enzyme breaker is added to the biodegradable slurry to reduce the viscosity of the biopolymer once the fracture is emplaced in the subsurface. Appendix A contains the Material Safety Data Sheets (MSDS) for each product. The only listed ' hazardous chemical ingredient in the enzyme breaker is sodium chloride. The ZVI contains less than 0.2% chromium on a weight basis. Therefore, this parameter has been added to the monitoring schedule. In 2001 a similar installation method was used to install a permeable reactive barrier (PRB) at a former DuPont facility in Oakley, California. The PRB was constructed biy using vertical ' hydraulic fracturing to inject a mixture of granular iron and biodegradable slurry . The ZVI mesh ranges from — 18 to + 84, similar to mid-sand size, this ZVI has been previously used in California, including the Central Valley. Appendix A contains iron leaching data supplied by ETI; no separate testing of the iron is proposed. ' 5. Contineency Plan/Capture Zone The proposed action is located in the central portion of the property well within the property ' boundaries. The groundwater velocity is considered low (likely less than about 10 feet per year) and the plume is considered stable. The compliance point for the aquifer would be monitoring well MW-413. Adverse effects on the groundwater at this location would be abated according to ' the type of constituent encountered. This same iron was also used at BP-Gardena(LA Water Board)and Sierra Army Depot(Lahontan Water Board and Sacramento DTSQ. RACONTGRAMCC14Cargill\French Camp\Waste Discharge Application\supp info 6-29-04.doc 12