"Cleanup Duty," Feature Article, February 2008

cleanup duty

Remediation of an old military landfill illustrates trends in environmental engineering.

by Don Plenderleith

Managing environmental impacts is a high priority for Canada's Department of National Defence. And when it learned that an old military landfill was posing a potential risk to a water course near the capital, the DND knew it had a new duty to perform for the country.

Public Works and Government Services Canada, which manages many of the military bases in the Ottawa region, commissioned the environmental and geotechnical firm Golder Associates Ltd. to provide engineering supervision and support for remediation of the site. The remediation of the former military landfill site, conducted in February and March 2006, not only cleaned up a polluted part of the Earth, it also pointed to some of the current best practices being used to protect the environment when working on military properties.

While having civilian organizations involved in military base remediation projects is common in some parts of the world, as far as we know, this is the first time such a remediation was done in this way in Canada. Outsourcing to the private sector freed up DND's resources for other work.

Downrange: Cleanup of an old dump near an active firing range required caution in managing personnel and hazardous wastes.

The landfill site is adjacent to the Delta Range of the Connaught Ranges and Primary Training Centre, an active facility used by the Canadian armed forces. It lies close to the shoreline of the Ottawa River, northwest of the city of Ottawa, and contained a variety of materials that were dumped over a period from the 1940s to the '70s. Site investigations revealed that the landfill contained some mechanical debris from target maintenance, paint cans with paint residue in them, broken concrete, and hydrocarbon-impacted soils. Its location close to the river and the leachable nature of some of its contaminants made it a high priority with DND for site remediation.

Small plumes of hydrocarbon-contaminated groundwater were identified within the landfill, but sentinel wells along the shoreline showed that the chemicals had not yet reached the shoreline or the river. Overland erosion was occurring, though, and metals-impacted soil was being transported from the landfill to the shoreline to fall to the bottom as metals impacted sediment.

Golder Associates worked on this project from 2002 to 2006, with a scope of work that included conducting environmental site investigations, ecological and human risk assessments, remedial options analysis and recommendations, and developing the remediation plan. It also involved developing tender specifications, monitoring excavations of contaminated zones, quality control, wildlife-protection measures, and final project delivery.

Remove or contain: Protecting the Ottawa River was both the motive for the cleanup and one of the chief concerns of the cleanup contractor.

Magellan Engineering of Ottawa provided real-time air monitoring, and Hazco Environmental Services of Calgary was contracted for earthworks.

On the two-hectare (five-acre) site, three priority areas were excavated and backfilled with clean material. Inert waste, such as concrete, bricks, and steel, were segregated from the contaminated soil on-site, which reduced the amount of material that had to be trucked off-site as contaminated material. In all, some 2,200 metric tonnes (2,425 U.S. tons) of impacted soil were removed from the site, but since about 500 tonnes (550 U.S. tons) of inert waste remained on-site, this reduced disposal costs and saved landfill space.

A permeable landfill cap of sand and silt was installed, with an angle of four degrees for drainage, covered with topsoil and planted with trees and grass. Shoreline protection was installed to protect the cap during river ice breakup and flood conditions.

Meeting the Goals

Essentially, this response used a combination of source removal (dig-and-dump) and risk management (covering lightly contaminated areas with the soil cap) to meet DND's goals.

The site posed some special challenges due to its military past. Over the 40 years that the landfill site was in operation, it was used for disposal of a wide range of military waste. This meant there was potential for unexploded ordnance, and special measures had to be taken.

Initial site investigation found evidence that hospital laboratory waste had been disposed of on-site, meaning there was a need for measures to protect workers from chemical and biological hazards. The worker protection level was Level C, which required hazardous materials (HazMat) suits with chemical-resistant gloves and boots and full-face masks and filtered air supply using canister-type filters.

Other contamination came from hydrocarbons, including accelerants used to burn waste, possibly including diesel fuel and stove fuel.

Parts of the Connaught range continued to be used for live firing exercises during the remediation process, so employees had to be diligent about signing in and out, and staying strictly within the designated site limits. The work had to meet a tight deadline so the military's spring training could start on schedule.

The Connaught landfill cleanup project also faced environmental challenges due to its location beside the Ottawa River and adjacent to two wetlands. Growing understanding of the importance of protecting groundwater and surface water from contamination meant that the project had to meet particularly stringent regulatory requirements. Mitigation steps included having the work carried out in winter, when potential contaminants are least volatile.

Protecting the Birds

The site is a federally protected migratory bird sanctuary, and a designated area of natural and scientific interest by the Ministry of Natural Resources of the province of Ontario. Some of the property is Class 1 provincially significant wetlands. This put the project under time pressures beyond the military's training needs. Work had to be completed before the start of the birds' spring nesting season.

The Ottawa River freezes up to a foot thick with ice in January and February. Ice breakup and high water due to snow melt in late March, while the remediation project was under way, posed its own construction challenges, due to potential erosion of the shoreline. Sediment could have been washed into the water if shore-protection measures had not been completed on time.

Floating silk curtains were installed in the parts of the river that were free of ice cover to contain potential sediment releases during construction. The curtains were made on-site by sewing a sleeve on the top and bottom of standard linear silt fencing. Long noodle-shaped swimming pool floats were put into the top sleeve and a length of chain was put into the bottom sleeve. The floating silt curtain was staked in place at a distance from shore so that the bottom of the curtain touched the river bottom. It thus prevented any sediment from the earthworks from being carried into the river beyond the curtain. As it turned out, good site management helped ensure that, in fact, no sediment was released into the river, but if that had occurred, the team was prepared to recover this material and dispose of it along with the other potentially contaminated soil.

Nesting instinct: Golder had to factor into its plans the relocation of the nesting site for a colony of turtles to protect the landfill cap.

Once site remediation began, plans had to be changed quickly, because Golder discovered that parts of the landfill site were dotted with holes that indicated it was being used as a turtle nesting site. This caused concern that, in building their underground nests, the turtles would dig through the landfill cap and expose contaminated soil. This meant a need to create a replacement turtle nesting habitat in a safe area, and find ways to encourage the turtles to use it rather than the area covered by the cap.

Through a literature review, Golder's bioscientists determined what kind of aggregate would be most acceptable to the turtles as nesting material—a specific mix of sand and gravel, rounded to protect the turtles' feet from cuts. Because this aggregate mix was not available off the shelf from any local supplier, it had to be custom-prepared.

As the landfill site's Ottawa River shoreline would be covered with rip rap—loose rock underlain with finer aggregate, in turn underlain with filter cloth to hold the fines in place—it would have been difficult or impossible for the turtles to reach the new nesting site from the water. Accordingly, a sand-covered turtle pathway was built through the rip rap.

Happy Turtles

Much to everyone's relief, the turtles liked their new facilities. In the spring of 2006, 20 nests were found in the alternative nesting habitat, with hatched eggs in them.

Now the only sign that a small landfill is present is a slight rise in the topography. The landfill cap is vegetated with grass and shrubs to consolidate the soil cover layers and prevent their erosion. Given that the site is behind the target area for one of the firing ranges, it doesn't get much human traffic, but its landscape is in keeping with the surrounding area, and the site poses no more threat to the local ecosystem.

Success in this project was based partly on solid planning, a good understanding of the client's needs, and the combination of several disciplines, including the biosciences, to reach the right result.

Don Plenderleith, a professional engineer, is senior project manager and federal client service team leader in the Ottawa office of the environmental and geotechnical firm Golder Associates Ltd. Melanie Talbot, an environmental advisor managing the environmental portfolio with Public Works and Government Services Canada in Ottawa, contributed information to this report.