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INFORMATION SHEET OER NO: R5-2008-0149 • 1 <br /> IN-SITU GROUNDWATER REMEDIATION AT SITES WITH VOLATILE ORGANIC <br /> COMPOUNDS, NITROGEN COMPOUNDS, PERCHLORATE, PESTICIDES, <br /> SEMI-VOLATILE COMPOUNDS AND/OR PETROLEUM HYDROCARBONS <br /> Volatile organic compunds (VOCs), petroleum hydrocarbons, perchlorate and <br /> fumigants have impacted groundwater at numerous sites within the Central <br /> Valley Region and cause or threaten adverse impacts to existing and potential <br /> beneficial uses of groundwater resources. Those sites are being required to <br /> clean up the pollution and restore the beneficial uses of the groundwater. This <br /> cleanup can take many forms. The two most common methods of cleanup of <br /> groundwater pollution are pump and treat, and in-situ remediation. The operation <br /> and discharge of a pump and treat system is generally regulated under site- <br /> specific or general waste discharge requirements. Prior to this General Order, in- <br /> situ groundwater remediation projects have had site-specific waste discharge <br /> requirements issued. The process to develop and adopt site-specific waste <br /> discharge requirements can be lengthy. Many in-situ treatment processes have <br /> common components and issues that can be regulated under general waste <br /> discharge requirements. <br /> In-situ remediation of groundwater pollution at most sites includes the use and <br /> application of biological, chemical, and/or physical treatment processes. These <br /> processes include addition of oxygen, chemical oxidation/reduction, and the <br /> addition of nutrients, carbon and/or bacteria to enhance biodegradation. The <br /> method of delivery can be via injection to soil or groundwater insitu, or via <br /> groundwater recirculation (extraction and treatment with return of treated <br /> groundwater to the impacted aquifer zone). In most instances the in-situ <br /> remediation processes will cause reducing or oxidizing conditions within the <br /> aquifer in order to either reduce or oxidize the target pollutant. The remediation <br /> processes can result in exceedances of water quality objectives that are <br /> generally limited in duration and/or in a relatively small portion of the aquifer. <br /> These waste discharge requirements allow exceedances of water quality <br /> objectives to occur while oxidation/reduction processes are taking place, but only <br /> within the treatment zone. <br /> Oxidation/reduction reactions take place when an electron is transferred from <br /> one compound to another. The electron donor becomes oxidized, and the <br /> electron receptor becomes reduced. These are always coupled reactions. If a <br /> compound is reduced, another must necessarily be oxidized to provide the <br /> electron. Reducing environments are typified by the absence of oxygen and are <br /> also referred to as anaerobic environments. Oxidative environments contain <br /> oxygen and are also referred to as aerobic environments. <br /> Reducing Environment Processes <br /> The primary reduction processes that are effective on perchlorate and VOCs are <br /> anaerobic in nature as aerobic processes are generally not effective on most <br /> highly chlorinated VOCs. Aerobic dechlorination or aerobic cometabolism of <br /> perch loroethylene (PCE) and trichloroethylene (TCE) has not been successful at <br />