Date of this Version
Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro-1 ,3,5-trinitro-1 ,3,5-triazine (RDX). Laboratory and pilot-scale experiments were performed to quantify the efficacy of permanganate to remediate RDX-contaminated groundwater. Laboratory investigations were conducted to determine the effects of permanganate concentrations and temperature on RDX destruction kinetics as well as to determine the Permanganate Soil Oxidant Demand (PSOD) and permanganate (Mn04-) transport properties.
Batch and column experiments showed that the Todd Valley aquifer sands contained a low PSOD indicating that permanganate mass consumption by the aquifer would be minimal. PSOD experiments also showed that the PSOD of the aquifer increased as the permanganate concentration increased. Batch experiments showed that the presence of Todd Valley aquifer media had little effect on RDX destruction kinetics and that RDX destruction kinetics and RDX mineralization increased with increasing permanganate concentrations. Batch experiments were conducted using RDX contaminated groundwater from the permanganate injection site (Co = 210 μg/L) where there where no appreciable changes in RDX degradation kinetics. Additional batch studies were conducted to observe temperature effects on RDX degradation kinetics where it was shown that lower temperatures slow down RDX degradation.
To evaluate the efficacy of permanganate to remove RDX under field conditions, a pilot-scale demonstration was performed in a 9 m by 15 m well field. Groundwater was extracted from a center extraction well, spiked with permanganate and bromide, and fed into two injection wells. Groundwater was then sampled biweekly for 8 weeks in monitoring wells down gradient of the injection zone. Results showed that RDX concentrations decreased 73 to 80% following injection. Despite problems encountered in getting the permanganate uniformly distributed across the injection zone, pilot-scale results provide proof-of-concept that permanganate can be used for in-situ chemical oxidation of RDX-contaminated groundwater.