Steel’s Legacy Contained – Remediation of the Sydney Tar Ponds and Coke Ovens Site in Sydney, Nova Scotia
The former Sydney Tar Ponds and Coke Ovens sites resulted from a century of steel-making in the heart of downtown Sydney, Nova Scotia. From the turn of the last century until 1988 when the coke plant shut down, the lands were subjected to a...
The former Sydney Tar Ponds and Coke Ovens sites resulted from a century of steel-making in the heart of downtown Sydney, Nova Scotia. From the turn of the last century until 1988 when the coke plant shut down, the lands were subjected to a barrage of contaminants. Present on the site were heavy metals, polychlorinated biphenyls (PCBs) and coal tar — a mixture of benzene, xylene, toluene, and polycyclic aromatic hydrocarbons (PAHs). These chemicals migrated downstream to the Muggah Creek estuary via the Coke Ovens Brook where they formed a tar-like sediment up to 6 metres thick. As a result, the estuary became known as the Tar Ponds.
As well, Coke Ovens Brook and nearby Wash Brook drain a 22.5 square kilometre urban watershed that conveyed combined sewage to the Tar Ponds until 2002 when an interceptor system and treatment plant were installed. Slag, a relatively inert steel plant by-product, was also deposited into the estuary, effectively moving the northeast shoreline up to 800 metres southwest.
The combined North and South Tar Ponds covered an area of approximately 31 hectares and contained approximately 650,000 tonnes of impacted sediments.
To the east, the adjacent Coke Ovens Site covers approximately 68 hectares. Long batteries of steel frame ovens lined with refractory brick processed coal into metallurgical coke. Rail tracks ran across the site to transport coal to the ovens, and coke from the ovens to the steel mill. A coal-tar refining plant operated adjacent to the site.
After the coke plant shut down, numerous abandoned buildings, open pits, large smoke stacks, storage tanks, asbestos debris, service tunnels and piles of coal, coke and sulphur remained. Under the site a maze of abandoned sewers, process and coke oven gas lines was left in place.
The nuisance of the abandoned facility and by-products, legacy contaminants and unsafe physical conditions led to the pressing need for remedial action. The quantity of materials with concentrations exceeding risk based site-specific target levels remaining on the Coke Ovens site was estimated to be 1,300,000 tonnes.
The Clean Up Trail
Sydney (population 9,000 in 1901, now 3,200) had developed around the steel mill and the adjacent coke plant. Residential, commercial and transportation infrastructure literally took root at the plant boundaries. Even after the steel works closed, the site continued to release tar-like byproducts into Coke Oven Brook, and at low tide, tar and sewage odours from the tar ponds were noticeable in the adjacent downtown commercial and residential neighbourhoods.
In 1982 Fisheries and Oceans Canada found PAHs from the tar ponds in Sydney Harbour lobsters, which led to the shutdown of the lobster fishery in the South Arm of Sydney Harbour. The commercial fishery remains closed to this day.
In 1986, Canada and Nova Scotia signed a $34-million agreement to dredge the tar ponds and pump the sediments through a mile-long pipeline to a fluidized bed incinerator and power plant. The incinerator was completed and passed required air emissions tests in 1994, but the pipeline system proved unable to handle the thick, lumpy, debris-laden sediment. It was also discovered that some of the sediments contained PCB’s that the incinerator was not approved to burn and the project was terminated in 1995.
A second clean-up option was explored in 1996 when Nova Scotia discussed a plan to bury the tar ponds under steel plant slag. By this time the project had attracted local and national public interest. With their concerns about being exposed to contaminants and long term environmental consequences, the local public insisted on having a voice in the development and evaluation of the clean-up.
In 1999, a community organization, the Joint Action Group (JAG) with a mandate to seek community consensus on the clean-up options was founded and our company, Conestoga-Rovers & Associates (CRA), was retained by Nova Scotia as the project management consultant. We provided technical leadership, project management, and guided the consultative process. JAG held more than 1,000 public meetings. People expressed a strong preference to use proven technology, but it was not possible to determine a clear consensus on the preferred clean-up technologies.
Two years later, the Sydney Tar Ponds Agency was formed by the Government of Nova Scotia to manage the current remediation effort. Around this time, the remaining coke oven structures were demolished, the adjacent municipal landfill was capped, and surface drainage improvements were made to divert water away from contaminated portions of the site. An interceptor sewer system was constructed to divert raw sewage away from the tar ponds.
By May 2004 the Governments of Canada and Nova Scotia had announced a 10-year plan to clean up the site at a cost of up to $400 million. A remedial action evaluation report (RAER) had been conceived by a consortium of consulting engineering companies that included Jacques Whitford, Dillon, ADI and CBCL (JDAC). They recommended solidification/stabilization as the primary tar ponds treatment technology, with incineration of tar ponds sediments that contained PCBs. The Coke Ovens contaminated materials would be managed in place, with groundwater collection and treatment used to protect realigned and lined surface water channels. An independent Joint Review Panel held under the Canadian Environmental Assessment Act held during April and May 2006 determined that incineration would be dropped from the plan. Otherwise, the RAER conceptual remedial plan is the one that has been implemented.
Remedial Action – Solidification, Stabilization
and Coping with Surface Water
The preliminary remediation work had included the re-routing of surface water around the Coke Ovens Site and the construction of a rock barrier at Battery Point, the boundary between the Tar Ponds and Sydney Harbour.
The primary remedial action at the Tar Ponds themselves was solidification and stabilization of the sediment with cement powder. The entire contents of the ponds were thoroughly mixed with cement powder in-situ, using either a large track hoe or a specialized mixing auger mounted on a track hoe. The sediments reached 6 metres down and were mixed in cells that varied between 150 and 300 cubic metres. Depending on the sediment’s water content, each cell received one truck load of cement powder of approximately 35 tonnes. Steel mill slag was added to some solidification/stabilization cells to improve the mix performance at specific locations. Each cell was typically built adjacent to a previously mixed cell, with production varying between 4 and 14 cells per day depending on the work area logistics and cement availability. Sediments from Coke Ovens Brook and its connector were transferred and incorporated into the Tar Ponds mix.
The resulting monolith has a thickness that varies from approximately 2 to 6 metres. The solidified material had to meet a minimum unconfined compressive strength of 0.17 MPa, a maximum permeability of 1×10-6 cm/s, and a maximum site specific leachate criteria for numerous contaminants before being accepted as complete.
With Coke Ovens Brook and Muggah Creek, two major urban water shed surface drains, crossing the work area, temporary dams and pumps had to be put in place for three years to allow the solidification and stabilization activities to be performed under dewatered conditions. A new Muggah Creek Channel lined with armor stone was constructed in the solidified sediment. Measuring up to 20 metres wide and 2 kilometres long, this new channel now conveys upstream urban run-off surface water through the remediated site, while accommodating the influence of ocean tides on the flow.
The stabilized tar pond sediment is being protected with a low permeable soil cap consisting of a vegetated layer over a 1.1 metre thick cohesive soil that has a maximum permeability of 1 x10-6 cm/second. It overlays a geosynthetic drainage layer.
The old Ferry Street
Bridge that provided access to the steel mill across Muggah Creek has been replaced with an eloquent new 33-m precast concrete girder structure. The new bridge provides a valuable new public road link between downtown Sydney and Whitney Pier, east of the former steel mill.
On the former Coke Ovens site the remedial action included injecting cement grout into abandoned underground sewer, process and gas lines in order to prevent them conveying impacted groundwater to nearby Coke Ovens Brook. The brook was rerouted, a pipe and media groundwater collection system was installed, and a groundwater treatment plant was constructed. An engineered low permeable soil covers the entire site.
When finished, the remediated Coke Ovens site will permit commercial development, although it will be subject to covenant restrictions on the type of foundations that can be used and the depth of new utilities.
A New Vital Public Space
The once contaminated marine estuary and former coke ovens are now remediated and the land will be transferred to the Province of Nova Scotia to maintain and monitor for a minimum of 25 years. A public celebration is being planned by the Province of Nova Scotia to mark the completion of the project and the opening of the new park on Labour Day weekend this year.
The lands now include public space with walkways along the new channels and an outdoor amphitheater. As part of the project’s “Future Use” plan there will be permanent art exhibits, a children’s playground, sports fields, concession and washroom facilities, and parking. Final construction work on these amenities is expected to be complete in the fall of 2013, ahead of the March 2014 conclusion of the Canada-Nova Scotia cost share agreement.
Long Time to Complete
It has been suggested that the Sydney Tar Ponds and Coke Ovens remediation project has taken a very long time to complete. There are many complex reasons, but in short, as this was one of Canada’s first major environmental cleanup projects, a long learning curve was required before there was sufficient information about the problem to justify committing tens of millions of taxpayer dollars to develop the appropriate remediation approach.
The extensive public participation added to the timeline, but this was a major contributor to the project’s success and was necessary after two successive clean-up attempts had not been fully successful. Once the May 2004 memorandum of agreement between Canada and Nova Scotia occurred, the design and construction of the remedial action progressed as rapidly as possible while remaining consistent with fiscal responsibility for the public purse.
With multiple work activities taking place on the project simultaneously, one of the greatest challenges was coordinating the efforts of the many entities (consultants, contractors, regulators, etc.). In this, the governance model put in place by the Governments of Canada and Nova Scotia which included having an independent engineer was critical to the project’s success. As Canadians are faced with more large scale remediation projects, it is imperative that the lessons learned from the Sydney Tar Ponds and Coke Ovens be carefully analyzed and employed on future projects.cce
Alan Van Norman, P.Eng. is vice-president with CRA based in Waterloo, Ontario, He is project director for CRA on the Sydney Tar Ponds and Coke Ovens site remediation project.
Client-owner: Nova Scotia Transportation and Infrastructure Renewal /Public Works & Government Services Canada
Project manager, 2000-2003 & Independent engineer for owner, 2005-present: CRA (Alan Van Norman, P.Eng., Jeroen Winterink, P.Eng., Holly Sampson, P.Eng., Hilary Fitzgerald)
Detail design engineer, construction oversight, final clean-up: AECOM (Bruce Noble, P.Eng.). 2006 environmental assessment: AMEC . Other key players: Dillon (env. monitoring); Stantec (quality assurance/design engineer for Future Site Use project); All-Tech (air monitoring); exp (quality control, construction).