ENERGETIC MATERIAL TRANSPORT IN THE VADOSE ZONE AT THE ARNHEM ANTI-TANK TRAINING RANGE, CFB VALCARTIER, CANADA

The Arnhem anti-tank training range has been used at the BCF-Valcartier military base since the 70’s. The ammunition used for training is the M72 rocket which has an explosive charge made of 300 g of Octol (60% HMX, 30% TNT and 10% RDX). The misfires of M72 rockets leave unexploded charges at the soil surface and the rain and snow melt waters dissolve and transport energetic materials (EM) into the ground water through the vadose zone. Since 1998, a hydrogeological study has been on-going at the range to understand the behaviour and the fate of EM in the unsaturated and in the saturated zone. The first characterisation phase mainly focused on the saturated zone and the data obtained were integrated in a 3-D numerical model representing groundwater flow and solute transport. This paper reports on the second characterisation phase focusing on the unsaturated zone.

The characterisation of the unsaturated zone began in 2000. Five lysimeter boxes were installed at 0.5 and 1 m depths in three different locations around the anti-tank range. Octol and tracer (NaCl) were placed on the top surface of each lysimeter box to monitor water infiltration and EM transport during 10 months. These lysimeter boxes provide a mean to evaluate the biodegradation and the retardation factors of EM on site as well as an evaluation of the infiltration rates. The preliminary results showed that TNT may be partly adsorbed and partly biodegraded and photodegraded. The same is not applicable to RDX and HMX. A small quantity of HMX and RDX probably goes in solution in water. When HMX and RDX are in solution, a small part can mineralise or degrade under UV light whereas the majority of the mass in solution goes down to groundwater.

Laboratory experiments were also made to reproduce the behaviour of EM under unsaturated conditions. Four large sand column (0.21 m diameter) experiments were carried out with lengths of 0.5 m (2 columns), 0.9 m and 3 m. The columns were all put under the same conditions of irrigation and temperature and were all kept in darkness except for one of the two small columns (0.5 m long) which was placed under a UV lamp to determine the amplitude of EM photodegradation. Microcosm experiments were also carried out to evaluate EM biodegradation and mineralisation rates under unsaturated and aerobic conditions.