In Situ Remediation of Explosives Contaminated Ground-Water with Sequential Reactive Treatment Zones

摘要

Most explosives that occur as groundwater pollutants at DoD sites are nitro aromatic compounds (TNT, trinitrobenzene, and various di- and mono- nitrotoluenes) or nitramines (RDX, HMX, and Tetryl). Under favorable conditions, nitro aromatic compounds (NACs) react rapidly with zero-valent iron (Fe0), which suggests that permeable reactive barriers containing zerovalent iron (FePRBs) might be useful in the remediation of groundwater contaminated with explosives. Unfortunately, reduction of NACs by iron metal produces aromatic amines as the primary products, and these products are still substances of regulatory concern. As a result, fullscale implementation of FePRBs to treat explosives contaminated groundwater has been delayed until an effective treatment for the amines has been developed and tested. The goal of this project was to develop an oxidative treatment step to treat the products of nitro reduction, so that the combination would form a sequential reactive treatment zone (SRTZ) that could be used to reach treatment goals for TNT- contaminated groundwater under field conditions. To generate simulated effluent from an FePRB we prepared bench scale columns, packed initially with 100% construction-grade, granular iron metal. We found that 100% iron columns, even at flow rates as high as 125 ft/day, produced no TNT or degradation products. Some of the columns were operated for approximately 1600 pore volumes with no TNT or any reaction products detected (by HPLC) in the effluent. The capacity of these columns to reduce TNT and sequester all of the reduction products suggested that simple FePRBs (with out the additional treatment zones associated with an SRTZ), might be sufficient for full-scale remediation of TNT-contaminated groundwater.