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INFORMATION SHEET ORDER NO. R5-2008-0149 4 IN-SITU GROUNDWATER REMEDIATION AT SITES WITH VOLATILE ORGANIC COMPOUNDS, NITROGEN COMPOUNDS , PERCHLORATE, PESTICIDES, SEMI-VOLATILE COMPOUNDS AND/OR PETROLEUM HYDROCARBONS periodically. The soluble substrates are consumed rather quickly and must be frequently replenished . Substrates that are viscous are less mobile than soluble substrates , but they tend to last longer in the subsurface. Slow release materials such as vegetable oil or HRCT"", which are intended to be long lasting , may require a single or limited number of injections. The low mobility of viscous substrates may lead to non- uniform distribution and require different application mechanisms to achieve the desired distributions . These substrates are relatively immobile and rely on advective and dispersive qualities of soluble compounds (lactic acid for the HRC and metabolic acids for the oil) to deliver them throughout the subsurface (ITRC , 2007) . Moderate viscosity fluids such as emulsions of vegetable oil have a relatively high mobility as compared to solid or highly viscous materials that allows more uniform distribution within the aquifer. Emulsified oils slowly release hydrogen through fermentation of fatty acids . Other moderate viscosity substrates that could be used include , chitin , whey and oleate. Oxidative Environment Processes As with reductive processes, oxidation processes can be either chemically or biologically induced . A chemical oxidant removes electrons from constituents in the vicinity of the oxidant and the oxidant becomes reduced. In a biological oxidation process , one compound is the electron donor and another compound is the electron acceptor. An example of biological oxidation happens with fuel contaminants in groundwater. In an aerobic environment, fuel can provide the carbon and the electrons for microbial metabolism , and the oxidizing agent is oxygen, which is the electron acceptor. In the absence of oxygen , nitrate also serves as an electron acceptor. The fuel becomes degraded as it is oxidized . Remediation of groundwater pollution , including VOCs , benzene , toluene , ethylbenzene, xylenes, organic pesticides, munitions (i. e. , HMX, RDX) , petroleum hydrocarbons or MTBE can potentially be achieved using chemical or biological oxidation processes. This involves injecting oxidants directly into the source and the downgradient plume , or delivering oxidants by means of a groundwater recirculation system. The oxidant reacts with the pollutants , producing innocuous substances such as carbon dioxide , water, and chloride. The four main chemical oxidants used are permanganate, peroxide , persulfate and ozone . The ability of the oxidant to react with a certain contaminant in the field depends on kinetics , stoichiometry, thermodynamics and delivery of the oxidant. On a microscale, kinetics or reaction rates are the most important. The rates of