Passive in situ biobarrier for treatment of comingled nitramine explosives and perchlorate in groundwater on an active range.

Abstract

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and perchlorate (ClO4-) are common, and often co-mingled, contaminants at military ranges worldwide. This project investigated the feasibility of using a passive emulsified oil biobarrier plus a slow release pH buffering reagent to remediate RDX, HMX, and ClO4- in a low pH aquifer at an active range. A 33 m biobarrier was emplaced perpendicular to the contaminant plumes, and dissolved explosives, perchlorate, and other relevant parameters were monitored. The pH increased and the DO and ORP decreased after emulsified oil injection, leading to >90% reductions in perchlorate, RDX, and HMX compared to upgradient groundwater. Some nitroso breakdown products were observed immediately downstream of the barrier, but generally decreased to below detection limits farther downgradient. First-order rate constants of approximately 0.1/d were obtained for all three contaminants. Dissolved metals (including As) also increased in the wells immediately adjacent to the barrier, but attenuated as the plume re-aerated in downgradient areas. Biobarrier installation and sampling were performed during scheduled range downtime and had no impacts to ongoing range activities. The field trial suggests that an emulsified oil biobarrier with pH buffering can be a viable alternative to remove explosives and perchlorate from shallow groundwater on active ranges.