Environmental impact of military explosive munitions at General De La Rey Training Area, Potchefstroom

Abstract

Explosives are manufactured in the industry using energetic chemicals such as 2,4,6-Trinitrotoluene (TNT), Hexahydro-1,3,5-Trinitro-1,3,5-Triazinanane (RDX), Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine (HMX), Composition B and Tetryl, 1,3,5-Trinitrobenzene (TNB). Propellants generally contain Nitrocellulose (NC) combined with other energetic compounds. Published literature has shown that explosives are not completely consumed by detonation or deflagration during a firing event and this results in deposition of some of the explosive residues onto the ground, thereby causing contamination. Heavy metal contamination also occurs in training areas due to metal fragments from munitions castings and explosive additives. This study was conducted at General De La Rey Training Area to investigate the environmental impacts of explosive munitions. The unexploded explosive ordnance (UXO) locations were investigated by foot and vehicle reconnaissance, recorded and quantified. Soil and water samples were collected within the training area and two control areas adjacent to the study area and analysed for explosive residues using HPLC and for heavy metals using Microwave Assisted Acid Digestion and ICP MS. Nine areas used as UXO disposal and Open Burning/Open Detonation (OB/OD) sites were located and the amount and diversity of UXO determined. A total of 181 samples were collected of which 133 were soil samples and 48 water samples. Contamination from RDX and HMX contamination were dominant in control water samples from in orders of 100 μg/kg. Soil samples from all sectors of the military training areas (MTA) contained low concentrations of High Explosives (HE) in the order of 10 μg/kg. TNT transformation products were the most frequent detections. The study area was also contaminated with various concentrations of heavy metals. Most of the contamination was in soil samples from UXO sites and explosion craters. MTA soil samples exhibited higher metal concentrations, particularly Mn, Cu and Cr, than control samples. Hg and Cd exhibited the lowest concentrations in control soil samples. Contamination in water samples was minimal. Little overall variability existed between MTA and control water samples. The MTA exhibited slightly higher concentrations of heavy metals than control environments. More than 1000 UXO items from various types of explosive munitions were counted within the MTA. A total of nine UXO sites were found in the study area. The UXO consisted of mortars, 155 mm shells, antitank rockets, hand grenades, etc. UXO was only counted from the surface due to safety considerations. The overwhelming majority of UXO were 60 mm and 81 mm mortar bombs, which accounted for 38 % and 31 % of the total UXO.

The study concluded that contamination from both explosive compounds and heavy metals was detectable but not severe enough to warrant urgent clean-up operations. Although no indices were found for determining intervention level contamination for explosive compounds, toxicity data indicated that the detected concentrations were much lower than reported toxic levels. This was also the case with heavy metals. Individual samples exhibited hot-spots of high concentration where remediation may be required, such as the OB/OD sites at Sector B. The study further concluded that mere existence of UXO is an explosive hazard and recommended that all UXO must be rendered safe and cleared from the MTA. The SANDF needs urgent development of characterisation, monitoring and remediation strategies for controlling these impact of explosive munitions before contamination reaches costly toxic levels.