At the U.S. Army Natick Soldier System Center (NSSC) in Natick, Massachusetts, groundwater is being pumped and treated to provide containment of an historical trichloroethene (TCE) plume. Upon discovering 1,4-dioxane (an emerging contaminant not previously monitored) at one of the monitoring wells above the Massachusetts Department of Environmental Protection drinking water goal of 3 µg/L, the existing on-site groundwater treatment system required augmentation to continue maintaining plume containment and meeting allowable discharge limits. Existing treatment consists of air-stripping and granular activated carbons, which both have a low efficiency for treating 1,4-dioxane. The concentration of 1,4-dioxane in the TCE plume requiring treatment is less than 100 micrograms per liter (µg/L) and approximately 10 to 20 µg/L in the 4 to 6 gallon per minute (gpm) combined discharge stream from three new extraction wells. Because 1,4-dioxane was only identified in a isolated portion of the TCE plume and not in the 75 to 90 gpm flow to the existing treatment system from this TCE plume and others, a goal was to provide in-situ or wellhead treatment for the 1,4-dioxane and not to treat the 75 to 90 gpm flow.
An engineering study was conducted to evaluate 1,4-dioxane and TCE treatment options, with key considerations being that 1,4-dioxane was detected at a low concentration, the extracted water was high in total suspended solids (TSS) and iron oxides, flow-rates needed for containment were small (< 6 gpm), 1,4-dioxane was highly localized, and the size of the physical plant had to be small. Viable options that were considered included the following Advanced Oxidation Processes (AOPs): Fenton's Reagent, hydrogen peroxide with ultraviolet (UV) light, hydrogen peroxide with ozone, and catalyzed persulfate.
Based on the engineering study, ex-situ application of Fenton’s Reagent was selected as a practical cost-effective solution. Bench-scale jar testing demonstrated that naturally occurring iron found in the water was sufficient to provide the metal catalyst needed for the Fenton’s reaction, and that stoichiometrically over-dosing hydrogen peroxide would decrease treatment residence-time necessary for achieving remediation goals and compensate for hydrogen peroxide dissipating side-competition reactions.
Kiker, Jackson H.; Connolly, James B.; Murray, Willard A.; Pearson, Stuart C. Pearson; Reed, Stanley E. Reed; and Tess, Robert J.
"Ex-Situ Wellhead Treatment of 1,4-Dioxane Using Fenton's Reagent,"
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy:
Vol. 15, Article 18.
Available at: http://scholarworks.umass.edu/soilsproceedings/vol15/iss1/18