Perchlorate contamination arises primarily from the manufacture and disposal of ammonium perchlorate—an oxidant found in solid rocket fuel, flares, and munitions. Known to inhibit iodide uptake by the thyroid, perchlorate's health effects at low-level exposure are controversial; however, it is an especially sensitive issue due to its high solubility and mobility in groundwater.
Since perchlorate is readily biodegradable by bacteria, in situ bioremediation is as an affordable and effective treatment option. To optimize the biodegradation process, CDM has developed a new in situ bioremediation technology called gaseous electron donor injection technology (GEDIT). This CDM-patented process involves the injection of electron donors as a gas, rather than as liquid, into the soil to stimulate anaerobic, biological reduction of perchlorate. In situ methods involving water injection are unlikely to succeed because the liquids are not easily distributed through the soil.
While shallow soil contamination can be effectively treated using excavation, perchlorate deep in the vadose zone—the soil located above the water table—represents a long-term source of continuing groundwater contamination due to perchlorate's leachability and the impractical and costly remediation challenge of using deep excavation methods. GEDIT may be the only technology that is capable, practical, and effective for treatment of perchlorate in deep soil.
GEDIT is based on, but the reverse of, bioventing—a common in situ remediation process used for remediation of fuel hydrocarbons, such as gasoline and jet fuel. Bioventing involves injection or drawing of air into the ground to provide oxygen to promote biodegradation of hydrocarbons. In addition to perchlorate, GEDIT also stimulates the biological degradation of nitrates, chlorinated compounds, halogenated organics, energetics, and other pollutants. It is estimated that average savings per site could be $6.6 million over excavation and disposal, and $2.6 million over excavation and ex situ bioremediation.
For more information, please read Looking Deep to Remediate Perchlorate (PDF).