Concerns exist about the potential impact to the surrounding environment from release of energetic compounds during live-firing range exercises conducted within military training ranges in Hawaii and elsewhere in the Pacific Region. The Makua Military Reservation (MMR) on Oahu has been in operation since the 1940s and currently contains the only combined-arms live-fire training range available in Hawaii. At MMR, the energetic compounds RDX, HMX, and DNT have been detected in Open Burning/Open Detonation (OB/OD) area soils and vadose zone pore water at concentrations above Environmental Protection Agency Region IX Preliminary Remediation Goals. The objectives of this demonstration/validation project are to evaluate (1) in situ degradation of energetic compounds within OB/OD soils as a result of natural plant-mediated degradation and (2) in situ enhanced aerobic and anaerobic bioremediation with low-cost additives to promote the degradation of energetic compounds within the shallow vadose zone pore water and tropical soils.

Technology Description

Phytoremediation represents a potential preventive treatment for areas receiving new RDX, such as the live-fire training impact area. This project will evaluate the effectiveness of plants at reducing residual energetic contamination in near-surface soils within the root zone. A total of four lined test cells will be constructed within the OB/OD unit and filled with site soils impacted with a known initial concentration of energetic compounds. Some cells will contain Guinea grass (Panicum maximum). The concentration of energetic compounds in the soil, leachate, plant root, and plant shoot will be monitored to evaluate the effectiveness of the naturally occurring Guinea grass in reducing residual energetic compound levels in MMR soils.

Bioremediation addresses contamination remaining from OB/OD operations at deeper depths than the root zone. This project will evaluate the effectiveness of in situ enhanced aerobic and anaerobic bioremediation of RDX and HMX dissolved in vadose zone pore water in tropical soils beyond the root zone. Food-grade carbohydrate reagent solution (molasses) at a dilution of 1:20 will be applied with irrigation water to stimulate indigenous soil microbiota and allow enhanced growth of the indigenous microbes on two 25 x 25 foot test plots at the OB/OD area. Concentrations of energetic compounds will be monitored to study the effectiveness of the bioremediation methods.

Implementation Issues

If proven successful in tropical soils, the phytoremediation and bioremediation technologies will provide low-cost alternatives for remediation of RDX and HMX in shallow soils and vadose zone pore water. Such alternatives will assist the Department of Defense in meeting environmental requirements and sustaining live-firing range exercises at MMR as well as other live-fire training ranges throughout the Pacific Region. (Project Completed - 2008)