Ranges and other areas used by the Department of Defense (DoD) for testing new ordnance and for training personnel are common sites for environmental contamination with explosives. The munitions used by DoD contain a number of different explosive compounds including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in the fuse. Residues from munitions are dispersed over the soil surface and then serve as point sources for explosive compounds that can migrate into the soil and eventually contaminate the underlying groundwater. Technologies are needed to reduce the impact of range activities involving munitions on environmental resources.
This project evaluated a surface-applied material composed of peat moss plus crude soybean oil (PMSO) as a technology to prevent and mitigate near-surface soil contamination with explosive compounds, thereby protecting the subsurface and groundwater at active DoD ranges. The primary quantitative objective was to assess the effectiveness of the PMSO technology with respect to reducing the flux of dissolved explosive compounds in soil emanating from surface-deposited munition residues. This objective was examined during the Soil Plot 1 (SP1) demonstration. The primary qualitative objective was to assess the compatibility of the PMSO technology with DoD training activities at ranges. This objective was examined during the grenade range (GR) demonstration.
The PMSO technology was tested in two different types of demonstrations:
SP1 Demonstration - Nine aboveground plots containing native uncontaminated soil were established at the Massachusetts Military Reservation (MMR). Plots were instrumented for the collection of soil pore water and pore gases, as well as with soil moisture probes; a weather station was also set up to collect meteorological data. Three plots served as controls and received no PMSO, three received a 10 cm layer of PMSO (1:1 peat moss:crude soybean oil, PO1), and the remaining three received a 10 cm layer of PMSO (1:2 peat moss:crude soybean oil, PO2). Composition B detonation residues of approximately 1-mm size from an 81-mm mortar round were applied uniformly over the surface of each aboveground soil plot. Soil pore water samples, as well as drainage water samples, were collected over the course of 1.5 years and analyzed for explosive compounds. At the end of the demonstration, the plots were deconstructed and the concentration profile of residual explosives in the soil was determined. Results were used to calculate the explosive compound flux, and results from the different treatments were compared. Data were also used to refine the PMSO effectiveness model developed during an earlier Strategic Environmental Research and Development Program (SERDP) project (ER-1229).
GR Demonstration - A 10 cm layer of PMSO (1:1 peat moss:crude soybean oil, w:w) was applied across the surface of a 10 m x 10 m area in a single grenade range bay. After the PMSO was applied, hand grenade training continued. The redistribution of the PMSO was monitored and recorded using digital photography and image analysis.
The results from both the SP1 and GR demonstrations yielded the following conclusions:
- The PMSO material was very effective at reducing the migration of RDX into and through the soil when it was dissolving from surface-applied Composition B residues. The RDX flux reduction ranged from 25- to 100-fold in the PMSO-treated plots (10 cm depth of 1:2 peat moss:soybean oil) versus the control plots. MNX flux was also reduced 12- to 50-fold, depending on the depth. Dissolved TNT and HMX were not detected with enough frequency to allow calculation of fluxes of these compounds, but based on the previously developed model, the effectiveness for these compounds would be expected to be very high as well.
- It is expected that the PMSO would be effective at reducing the transport (flux) of other munition and propellant compounds including 2,4- and 2,6-DNT, nitroglycerin, and nitroguanidine based on the physico-chemical properties of these compounds, as wells as some preliminary laboratory results.
- Surface-applied PMSO would not likely be drastically affected by grenade (or other munition) detonations themselves, but it would be redistributed horizontally and mixed vertically into the soil in the treated area.
- Explosive ordnance disposal (EOD) activities that employ large quantities of C4 could result in smoldering of a surface-applied layer of PMSO.
Based on current results and model predictions, the PMSO material would be effective as a barrier to reduce explosive compound transport (flux) if it were either (1) applied and buried under a layer of soil 30 to 60 cm (1 to 2 ft) deep or (2) mixed into the top 15 to 30 cm (0.5 to 1 ft) of soil. These types of application would avoid most of the issues involving smoldering and generation of excessive fugitive dust. The exact depth of burial or mixing would be dependent on the type of training area at which the PMSO was being applied. For a hand grenade range, cratering is usually less than 45 cm (1.5 ft) deep, so PMSO burial at 60 cm should be sufficient. At a mortar target area, deeper burial may be needed due to deeper cratering, while treatment at a mortar firing point to capture and treat propellant residues might require burial at only 15 cm (1 ft), depending on the amount of heavy equipment or track vehicles that would be expected to be moving across the treated zone (i.e., the PMSO would need to be buried deep enough to prevent the vehicle traffic from digging up and removing the PMSO layer).
The PMSO technology is most applicable for portions of the range where unexploded ordnance (UXO) is not of concern, such as open burn/open detonation (OB/OD) areas and EOD training areas, as well as grenade training areas and mortar firing points. PMSO would also be applicable for inclusion as a sustainable range management technology for use in areas that have been cleared of all past UXO.