A Metallic Past
May 14, 2008
Along a large swath of remote northeastern New Brunswick land, a handful of men stand still. Their expectant eyes fixed on the same point. Then it happens. A deep sound like the forceful downbeat of a drum cracks the air, and the dirt-caked ground explodes in a dusty plume of metal and sand. When the clouds dissipate, the men, satisfied that the WWII munition is sufficiently destroyed, move on to their next target. That was eight years ago.
Today, survey and dig teams in brightly colored vests walk sections of this same land armed with different weaponry: high-powered metal detectors, real-time kinematic (RTK) GPS receivers and shovels. Their mission shares the same goal--except this time it isn’t as loud or as dirty. The goal, in short, is to verify how thorough the previous unexploded ordnance (UXO) clearance program of the former Tracadie Range military training base was conducted and how much, if any, residual risk of UXO still remains within Tracadie’s 18,000 hectares (44,479 acres) of public land.
“In the past, the clearances in Tracadie were conducted using very simple metal detectors and manual records,” says David Parkinson, manager of AMEC’s New Brunswick operations, the engineering consulting company managing the residual-risk project. “With advanced GPS equipment and geophysical technology, we can produce a map showing exactly where the equipment went, the anomalies detected, their precise location and their UXO potential. That assuredness lends much more credibility and defensibility to the findings and is a far more effective tool for assessing residual risk.”
The confirmation campaign is part of Canada’s Department of National Defence’s (DND) UXO and Legacy Sites Program, which aims to capitalize on today’s technological advancements to assess the effectiveness of the past’s clearance techniques. Initiated three years ago to reduce the risk of UXO remnants on all “legacy sites”--any property not owned by the DND that contains UXO--the DND began selecting target sites last year for UXO residual-risk assessments. First up on that list was the Tracadie Military Range.
Winning ProofThis first-of-its-kind project was also an opportunity for AMEC to propose and test Trimble’s ( www.trimble.com ) R8 GNSS (Global Navigation Satellite System) RTK solution. AMEC believed the system would meet the accuracy requirements of the project and provide the reliability and improved productivity needed to meet tight budgetary and project timelines.
Though AMEC had never before used the Trimble R8 GNSS system for UXO risk projects, Parkinson says the millimeter accuracy and technological capabilities of the GNSS system were instrumental in winning the Tracadie project.
“For this project, we need to have real-time accuracy to pinpoint anomalies and record the precise location of each anomaly to within twenty-five centimeters,” Parkinson says. “Achieving that same level of accuracy with post processing is possible but impractical. With the R8 system, we have that precision in real time, enabling us to verify in seconds that we are investigating the right targets and to accurately record what we find at each anomaly. Being able to demonstrate how we could achieve that level of accuracy was a definite determinant in winning this project work.
“Data quality objectives are intense on these projects, and with the reliability and precision of the Trimble technology, we can confidently present our results to the DND for further analysis and decision making,” he adds. “We predict the impressive performance of the technology will set the standard for the future approach for these projects.”
Tracing TracadieFor 55 years, from 1939-1994, Tracadie was the temporary home for thousands of army and air force soldiers as they honed their weapon-firing skills. In 1994, the range was deemed surplus by the DND, and the property was transferred to the province of New Brunswick in 1997 with the provision that the lands be cleared sufficiently of UXO to permit forestry, blueberry cultivation and recreational uses. For the next four years, the DND carried out UXO clearance work to mitigate the UXO risk to a satisfactory level.
In 2002, however, the province assessed the clearance work and became concerned that the residual UXO risk might be higher than anticipated. So, the DND commissioned AMEC in 2006 to conduct a comprehensive residual-risk audit (RRA) of the former range. After extensive study and fieldwork, AMEC teams concluded that additional UXO risk-mitigation measures were required in some of the former artillery-impact areas. The team prioritized those areas and recommended that geophysical and GNSS technology be used to further assess the specific areas.
In June 2007, DND assigned AMEC to pick up where it left off, launching the Legacy Program’s first substantial UXO residual-risk project and sending AMEC teams back to Tracadie in search of the telltale metallic signs of the range’s former life.
Testing a TechniqueBecause AMEC had conducted the 2006 RRA for Tracadie, project members had already compiled a comprehensive GIS database on the region complete with orthophotos, land-use maps, archeological constraints, environmental constraints and, most importantly, a map of all the previous clearance data--what was found, where it was found and at what depth it was found. They also had the prioritized list of particular areas that needed further study.
One of the first high-priority areas was known as the east risk zone, a 400-hectare (988-acre) area at the northern end of the range. The initial objective was to sample a percentage of the study area for possible UXO in order to characterize the UXO potential of the whole area based on the sample results and sophisticated statistical methodology.
Using the Trimble R8 GNSS system, a two-person crew first marked out a study grid of 40 1-hectare blocks. They pinpointed the southwest corner first and then positioned the three remaining corners, marking out 1-meter lanes for the crews to walk.
An R8 GNSS receiver was then mounted to a high-powered electromagnetic sensor to perform a digital geophysical survey of 25 percent of the 40 sample blocks. A team member pulled the sensor over the area of interest to detect the presence of all metallic items in the ground and to record their signal strength while the R8 GNSS system provided real-time positional accuracy of the sensor’s movements. The readings from the electromagnetic sensor, coupled with the continuous GNSS readings, were then post processed by sophisticated software to generate coordinates of anomalies or suspected UXO.
Through the considerable post processing of the geophysical survey data, the AMEC teams of up to 45 field workers at any one time plotted positions of the suspect UXO on maps and digitally flagged them through color-coded points. The field teams then used RTK-GNSS to re-acquire and flag the points of potential targets detected by the geophysical survey. At this stage, Parkinson says the RTK technology proved critical to the project.
“When you are going back into the field to re-acquire target positions, you need to be able to navigate back to them and to be sure you are at the right target,” he explains. “We rely on that fact--that we can accurately come back to points with the R8 GNSS receiver and be able to confirm that we are at the right position based on the real-time accuracy of the GPS and the signal strength of the item detected by the sensor.”
With the location and signal strength confirmation, the crews staked the target with a pin flag at its precise position for specialized UXO technicians to investigate. Using handheld magnetometers, the technicians again verified the positive signal presence of metal and gingerly dug it up. Any munitions found were carefully inspected to determine if they needed to be destroyed. All discovered ordnance was properly and precisely recorded, including the type of ordnance found, its position and status (live or nonexplosive), and the collected field data was uploaded into the GIS.
“Based on the number of anomalies, their signal strength and the number of solid shot rounds and munitions debris we found, it became clear that there was a main area of concern to the south and west of the area,” Parkinson says.
Turning their focus to the south and west of the first risk zone, a field team once again marked out eight 1-hectare sample blocks using the RTK receiver. For this more concentrated study site, they performed a complete geophysical survey of the entire grid, processing and analyzing the integrated data stream from the sensor and the GNSS unit to identify anomalies by size and strength. In studying the data, personnel identified the hot spots of greatest concern. The field teams then imported those coordinates into the survey controller software before going back into the field to accurately locate the targets for the UXO specialty teams to intrusively investigate.
All of the data collected for the east risk-zone study was then used to compile a complete map of the potential risk of UXO for the entire zone--a result, Parkinson says, that would not have been as accurate without the GNSS technology.
“With the real-time millimeter accuracy of Trimble equipment, we are able to stand behind our data and show with confidence the findings for each and every sample block in the east risk zone. That’s incredibly important when you are managing such a substantial public-safety mission.”
Expanding the UXO SearchIn parallel to the field teams at work in the east risk zone, crews were also employing RTK-GNSS technology in other high-priority zones in the northwest and south.
In the northwest, teams faced a much larger study area of 18 hectares (44 acres). Using a similar approach, they first used the Trimble R8 GNSS system to mark out a study grid. However, because of the larger study area, AMEC crews used a larger towed-array electromagnetic unit that provided a 3-meter-wide sensing swath. The sensors were physically pulled over the area of interest to detect the presence of all metal items in the ground and record their positions. The sensor and GNSS readings were then post processed to generate coordinates of suspect anomalies.
Crews would have then returned to the field to re-acquire the points of potential targets. But the inevitable snow dumps of New Brunswick forced the project team back inside. When the snow clears this spring, Parkinson says they’ll begin to investigate the hot spots.
“We know what anomalies we have, and thanks to the accurate positioning of the Trimble equipment, we know exactly where they are so we can easily go back and relocate those anomalies most likely to be UXO,” he says. “And from that exercise we can start to build a picture of the potential for the risk of UXO within the rest of that area.
“With 18,000 hectares of ground to cover and a delay in returning to the field, we need to have that precision and reliability to navigate back to those points,” he adds. “Without centimeter accuracy, it’s easy to question if you’re looking at the same target as before. Trimble provides us the assurance that what we’re looking at is the same target flagged yesterday.”
To date, AMEC teams have completely covered the 400 hectares of the east risk zone and have completed the geophysical survey of all 18,000 hectares of the two northwest zones. AMEC’s recommendations for the east risk zone were presented to the DND’s explosive risk rating subcommittee and are being evaluated to determine the best risk-management strategy for that zone.
Parkinson says that the accuracy they depend on in the field will also prove reliable for DND decision makers as they develop sound risk-management strategies.
“Previously, you couldn’t know with certainty if particular areas or anomalies were checked,” he says. “The accuracy of the Trimble technology provides a precise digital record of our work and results that will stand the test of time. That is credibility for today and for tomorrow.”