You are 13 years old, playing in the woods behind your friend’s country house, you glance down and notice a long shiny metallic object, you poke at it with a stick, you move it with your foot, you bend down to pick it up….
Just over half a century ago, the world was at war. The threat of global war still remains. Fortunately Canadian soil has been free from modern warfare; however, our hands are far from clean. Over 200 military instillations and/or training centers were established to support the war overseas and to defend Canadian borders. Each of these sites is classified by the Canadian Government as “Unexploded Bombs (UXO) Legacy Site”. There are an additional 1,100 UXO Legacy Sites offshore in Canadian waters and several hundred former US military bases protecting Canada’s northern border. Sixty years later and we have a big problem! Thirty percent of the munitions fired in training never detonated. These are what we call UXO. They are typically just below the surface as they burrow over time. These also become unstable over time. They were deposited during training (thankfully). Most of the real gunners were already at war or had been lost at war, and historical reports describe sixteen year old farm boys being recruited as gunners out of necessity. The inaccuracy reflects this; we have located bombs 5 kilometers from the target, in what was now a playground!
A little known fact is that over two dozen people have been maimed or killed by UXO in Canada or the US in the past two decades. The number is larger if you go back thirty or forty years. In addition to individual bombs from training, there are thousands of dump sites contaminated with UXO. The method of cleanup sixty years ago was to dig a hole and bury UXO or throw them in the water. This was done with complete disregard for future human occupancy and the existing wildlife. This is where the geophysicists come in. Our job is to locate the buried items, characterize the anomaly produced by the item, and then instruct former military specialists where to dig. The military specialists were part of the Explosive Ordnance Disposal (EOD) branch of the military and are known in the civilian world today as UXO technicians.
Geologists and geophysicists often study large features such as salt domes, which are the size of an office building. UXO, however, can be as small as a human thumb. For this reason positioning is as important as detection. We use magnetic and electromagnetic methods to detect the items and sub-centimeter GPS for positioning. Technological advancements have introduced new methods of detection, including ground penetrating radar (GPR) and acoustic methods. The deployment method for the detection system is typically ground-based but there are marine systems as well as airborne detection systems for larger UXO. Although the UXO are typically found in the first meter below surface, there are numerous challenges in detecting and recovering the items. As mentioned, a 20-mm projectile is about thumb size. A grenade is about as big as a baseball. The magnetic signature from these items is very small; therefore the data must be corrected and leveled to maximize the signal-to-noise ratio. The most popular detection instrument is the EM61 which is a time-domain electromagnetic all-metal detector. The GPS antenna is mounted directly over the detector for positioning. The geophysicist then processes the results and produces a map showing anomalies,which may end up as targets to be dug by UXO technicians. The data is processed using Geosoft Oasis Montaj software.
In the end, the contractor provides the government with a certification stating that the site remediation has been performed to the limits of the existing technology. One hundred percent risk can never be removed, but surely the efforts of the geoscientist and everyone involved with these projects has made our country a safer, cleaner place for now and the future.