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Sustained In Situ Chemical Oxidation (ISCO) of 1,4-Dioxane and cVOCs Using Slow-Release Chemical Oxidant Cylinders Patrick J. Evans, Jennifer Hooper, Michael Lamar, Dung Nguyen, Pamela Dugan, Michelle Crimi, Nancy Ruiz and Michael Pound Abstract Slow-release oxidant cylinders are an excellent fit for large, dilute dioxane plumes because (1) the slow-release feature is compatible with the low reaction rates; (2) the slow-release feature can be used to intercept plumes in a permeable reactive barrier (PRB) or funnel and gate (F&G); and (3) the technology is less expensive than conventional pump and treat with advanced oxidation. The approach is also versatile. It is applicable to an array of geology/geochemistry settings – the appropriate oxidant can be selected based on geology and geochemistry. This flexibility allows for system design that matches oxidant release rate, the dioxane transport rate, and the dioxane oxidation rate. The objective of this project is to demonstrate use of slow-release chemical oxidant cylinders to treat large dilute plumes of dioxane and CVOCs in situ. Permanganate and unactivated persulfate are capable of oxidizing dioxane albeit at low rates. A laboratory treatability test was conducted and determined that unactivated persulfate was capable of oxidizing dioxane and chlorinated VOCs. A demonstration was conducted to evaluate use of slow release persulfate cylinders for in situ treatment. Results demonstrated that dioxane and chlorinated VOCs were destroyed by more than 90% in areas where persulfate was delivered. Increases in sulfate and oxidation-reduction potential and decreases in pH correlated to destruction of contaminants. Persulfate sunk after it was released from the cylinders leading to predominate destruction of contaminants in deeper zones of the aquifer. Some destruction was observed in shallower zones. Technology Description Demonstration Results Performance Objectives Demonstration Approach Conclusions • Sodium persulfate with natural activation was capable of oxidation of 1,4-dioxane and CVOCs. • Greater than 99% contaminant destruction was observed. • High oxidant concentrations can lead to density-driven flow, especially in aquifers with small horizontal gradients. • A narrow radius of influence for the cylinder technology must be considered when designing a remediation system. "Funnel" Impermeable Barrier Wall "Gate" Oxidant Cylinders Points Groundwater Flow Slow-release oxidant cylinders are composed of either potassium permanganate and/or sodium persulfate formed into a cylinder with a paraffin wax binder. The cylinders can be placed in wells, in a permeable reactive barrier, or in the gate of a funnel and gate system. As aqueous contaminants flow past the cylinders, the oxidant is released and destroys the contaminant. The demonstration was conducted at Naval Air Station North Island Operable Unit 11 where 1,4-dioxane and chlorinated solvents are present. Two 18-inch boreholes were emplaced with sodium persulfate oxidant cylinders, which served as a mini-permeable reactive barrier. Groundwater was pumped to provide hydraulic control for the study because of the flat natural gradient. Total VOC (1,1-DCE, 1,1-DCA, cis-1,2-DCE, and TCE) concentrations (a) and percent removals (b), and persulfate concentrations (a and b) from CPT boring groundwater samples along the flow path downgradient of the persulfate cylinders and from the deep interval 12.5–14.5 ft below the water table. Geochemical parameters supporting natural persulfate decomposition and activation from the 12.5–14.5 ft interval along 289° (a) and 295° (b) flow paths downgradient of the persulfate cylinders. Oxidant Cylinder Wells Performance Objective Data Requirements Success Criteria Results Technology Effectiveness 1,4-dioxane and chlorinated ethene concentrations 90% reduction in 1,4-dioxane concentration or concentration reduced to <3 µg/L Exceeded; 99.3% reduction 90% reduction of chlorinated ethene co-contaminants Exceeded; 99.0% reduction in sum of 1,2-DCE, 1,1-DCA, cis-1,2-DCE, and TCE Sustainability / Longevity Oxidant and contaminant concentrations along flow path Rate of oxidant concentration change at any given location ≥0 mg/L/d over 1 year Not met; observed exponentially decreasing persulfate concentrations over time in cylinder wells with 9% predicted to be remaining after 1 year 90% contaminant removal is sustained for at least 4 weeks Exceeded for dioxane in cylinder wells; 90% reduction after 134 days; uncertain for CVOCs (See text for explanation.) Oxidant Transport and Destruction Oxidant concentrations along flow path Oxidant consumed to below detection at final down- gradient monitoring point or trends support its destruction along the flow path Met; 21 mg/L in deep sample from boring B21 7.9 m downgradient compared to 2,100 mg/L in deep sample from boring B14 4.3 m downgradient; trends also support further attenuation Technology Implementability / Secondary Impacts pH, ORP, persulfate, filtered metals (As, Ba, Be, Cd, Cr, Cu, Hg, Pb, Se, Tl, and U), bromate Filtered metals and bromate below background (upgradient well concentration) in the final downgradient monitoring point or demonstrated decrease in concentration along flow path; pH, ORP, and persulfate concentrations will be used to evaluate attenuation trends Met for pH, ORP, and persulfate; not analyzed for bromate and metals
