John Valkenburg, P.E.

Treating 1,4-Dioxane Commingled with Chlorinated Ethanes Using Extended-Release Potassium Persulfate

John Valkenburg, P.E., Senior Engineer & Technical Sales Manager Soil & Groundwater Remediation, Evonik Corporation

Background:

1,4-Dioxane is a probable human carcinogen and emerging contaminant of concern in the United States and in other countries.  Historically it was commonly used as a stabilizer with chlorinated solvents. 1,4-Dioxane is readily degraded by powerful oxidative radicals, but only biologically degraded under very specific circumstances. It is most often present at sites co-mingled with the chlorinated solvents it stabilized. The co-mingling of 1,4-Dioxane with chlorinated solvents complicates site treatment as 1,4-dioxane is typically treated using an oxidative or aerobic pathway and the chlorinated solvents are best treated with reductive pathways. Properly activated, persulfate forms both oxidative and reductive radicals, making it ideal for simultaneously addressing 1,4-dioxane and chlorinated ethanes. 1,4-Dioxane is atypical as compared to these comingled contaminants as it is miscible in water and has a very low organic carbon partitioning coefficient (Koc). As a result of these unique partitioning and transport characteristics, it is relatively more present in groundwater than on soil as compared to these comingled contaminants. Accordingly, smaller volume injections of extended-release potassium persulfate slurry are generally preferred for establishing oxidant/contaminant contact while avoiding ‘pushing’ out the more aqueous-phase 1,4-dioxane plume.  

Approach:

In Situ chemical oxidation using activated potassium persulfate was evaluated at two separate sites contaminated with a mixture of 1,4-dioxane, chlorinated ethenes, and chlorinated ethanes. The sites were first evaluated in a series of column reactors where site groundwater was run through the columns until the potassium persulfate had been consumed. Two different activation chemistries were evaluated at the bench: (1) iron activation using zero-valent and (2) alkaline activation using hydrated lime. Although both activation chemistries demonstrated complete treatment of 1,4-dioxane to below the detection limit, hydrated lime was selected for the subsequent pilot and full-scale field implementation due to its ability to also treat the full suite of contaminants present, including dichloroethanes (1,1-DCA and 1,2-DCA).    

Results:

Field data not only evaluated treatment effectiveness and the potassium persulfate persistence  under flow-through conditions in a Permeable Reactive Barrier (PRB) configuration. Performance monitoring showed a reduction of 1,4-dioxane, chlorinated ethene, and chlorinated ethane concentrations to below the detection limit within the PRB. Significant reductions in groundwater concentrations were also observed downgradient from the PRB over time. The geochemical data indicated that the potassium persulfate was persisting as expected based on the observed groundwater velocities and temperature.     

John has over 40 years of industry experience and is a professional engineer (Michigan). John and his wife enjoy their dog, cat, and 3 horses.