RELEASE FROM A WELL-BASED REACTIVE BARRIERS USING CONTROLLED-RELEASE KMNO4: A LARGE TEST CELL STUDY

Controlled-release KMnO4 (CRK) scheme has been recently developed as a semi-passive approach for long-term control of aqueous-phase plumes of chlorinated solvents in groundwater. A large-scale groundwater test cell facility (WúILúID = 4 m úI8 múI2 m) was constructed and used for investigations of release and spreading mechanisms associated with CRK in saturated porous media. The sandy medium in the large tank was characterized for hydraulic property and natural oxidant demand (NOD) using dispersion tests and batch experiments. Total of 110 field size CRK solids (OD x L = 5 cm x 150 cm; mass of KMnO4 = 1,764 g) were prepared by dispersing KMnO4 granules in matrices of wax-silica mixtures. A well-based reactive barrier system (W x L x D = 4 m x 2 m x 1.5 m) comprising three discrete barriers installed at 1-meter interval downstream normal to groundwater flow (1.72m/day) was constructed in the test cell for the release test. Each barrier comprised 40 delivery wells spaced in 10 cm intervals, and contained one CRK. Rates of permanganate release from a CRK in flowing water were initially high at ~8.7 g/day, and gradually decreased to ~0.2 g/day in 61 days, showing first-order release kinetics typical for a monolithic matrix-type controlled-release device. Permanganate concentrations in the test-cell ranged from ~1 to ~63 mg/L over 42 days, with generally higher concentrations in the reactive barriers and at depths, suggesting consumption by natural materials and density effect. These observations were described using model simulations. Release kinetics of controlled-release solids can be optimized by adjusting agent/matrix ratios or matrix structures to meet the specific goals of remediation. Such versatility of the controlled-release systems would provide target-specific remedial approach for contaminant plumes of variable nature.