Groundwater well injection—Oxidants may be introduced to the treatment zone through existing or new groundwater monitoring wells as a liquid, gas, or solid. This method relies on the natural migration of oxidants from the well into the formation. Injection wells need to be adequately spaced to allow for oxidant delivery to the entire treatment area.
Groundwater recirculation—A groundwater recirculation system may be used to extract groundwater from within or at the downgradient edge of the contaminated area, introduce oxidants and amendments aboveground, and reinject the groundwater upgradient of the treatment area. This approach can be used to increase the flow-through of oxidant through the treatment area, as well as to achieve downgradient containment of a contaminated groundwater plume.
Lance injection, jetting, and fracturing—Use of a high-pressure lance can create microfractures in soils that increase soil permeability and allow for direct injection of oxidants and amendments into a desired treatment area without the need for an existing or new groundwater well.
Soil mixing—For lower-permeability soils, soil mixing using tilling for shallow soil or an auger for deeper soil can be used to introduce oxidants to a treatment area.
PRB—Oxidants can be injected into the treatment zone of a PRB to oxidize the groundwater that flows through it. This approach can be used as a containment approach for a contaminated groundwater plume. Also, a PRB could be placed upgradient or within a treatment area allowing the oxidized groundwater leaving the PRB to flow through the treatment area.
There are also technologies that use electrical or other forms of energy to generate oxidizing and reducing radicals in aqueous solution and thereby destroy contaminants such as MTBE and other oxygenates. These technologies include ultrasound and electron beam (E-beam) treatment, and are primarily used in ex situ applications. Recently, however, ultrasound treatment has been proposed as a potential in situ application by incorporating ultrasonic transducers into a robotic self-powered mining head.82
Additional information relevant to the application of ISCO at sites in general or contaminated with MTBE and other oxygenates is available in the following Refs. [75,82-86].
24.8.4 Types of Projects Used in ISCO Treatment of Oxygenates
From the 323 MTBE projects in U.S. EPA's MTBE Treatment Profiles dataset, 21 projects were identified where MTBE was treated using ISCO. No ISCO projects reported treating other oxygenates. Four of the projects used ozone and 17 used hydrogen peroxide, either alone or with Fenton's chemistry.
Most of the 21 ISCO projects were performed at full scale (17 projects) at the time that their profiles were compiled. Eight of the 21 projects were identified as completed, and the remaining 13 as ongoing. In addition, while most14 of the projects used ISCO alone, seven projects supplemented ISCO with air sparging, pump-and-treat, SVE, or MPE.
24.8.5 Performance of ISCO in Treatment of Oxygenates
Tables 24.15 and 24.16 summarize performance data for the eight completed and 13 ongoing ISCO projects. The data presented in these tables show that ISCO (either alone or in combination with other technologies) has been used to remediate MTBE in groundwater from concentrations
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