Questions abound over plan to firm up the tar ponds
Weekend Feedback - Marlene Kane
Cape Breton Post
Sat., May 21, 2005
Early in March I asked Frank Potter of Sydney Tar Pond Agency why stabilization-and-solidification (S/S) was chosen for the majority of the tar ponds sediment when it has limited success on soils with high concentrations of organic contaminants. Parker Donham submitted my question and Potter's response, two months later, to the Post for publication (Weekend Feedback: Structural Stability the Main Aim, April 30).
My question came almost verbatim from a Joint Action Group government document called Considering Technologies Fact Book. Knowing that the tar ponds contains high concentrations of organic contaminants, I wondered why this method was chosen when it had only limited success, according to government's own document.
Several technologies showed "much promise for efficient and effective remediation of the Sydney tar ponds sediments" during the 2001-02 technology demonstration program. Some showed suitability and feasibility in producing commercial fuels from much of the tar ponds sediments, while others significantly reduced PAH and PCB levels in the sediment. Unfortunately, government selected none of these technologies.
During the demonstration process, the sediment was not actually stabilized, and long-term immobility of some organic compounds was not proved. This may be problematic because the tar ponds contains high concentrations of organic compounds.
The technology track record states that while S/S was successful commercially on materials with high inorganic impacts, it had less experience on organics. S/S did show "some indirect benefits in terms of improving sediment handling capabilities but its suitability and feasibility depend on further definition of specific remedial action objectives."
According to the government's plan for remediating the tar ponds, 120,000 tonnes of PCB-contaminated sediments will be excavated, dewatered and incinerated in a temporary incinerator less than two kilometres from Cape Breton University, and much closer than that to many residences. This technology was chosen despite the fact there were no PCB incineration test burns of tar ponds sludge during the demonstration.
Emissions from incinerating PCB sediments from the tar ponds have not been measured and the resulting ash from that process has not been tested, yet STPA vows it is safe. The plan is to construct an incineration facility first and then conduct a test burn.
Next, depending on which government report you refer to, either the top one to two metres (unspecified tonnage) or all of the remaining contaminated material (580,000 tonnes) in the tar ponds will be solidified and stabilized in place using a cement-like additive. Bearing in mind that the addition of solidifying agents like Portland cement can almost double the volume of contaminated material, it presents quite a vision.
Instead of getting rid of the tar ponds once and for all, the government
plan is to increase the volume by 40 per cent. This material will then be capped, likely using fill, layers of drainage material, and topsoil.
During the technology demonstration, complications were experienced within drummed samples of tar ponds sludge when methane gas was generated from the decomposition of sewage organics. This pressure forced some of the drums to become deformed, which required all to be vented to atmosphere. How will this methane gas and the pressure it creates affect the outcome of the S/S process and the surface cap?
If indeed only the top one to two metres of sediment is to be treated with S/S, how will the added weight of the top processed material affect the sludge underneath? Would the weight force the bottom material to move in one direction or another? Will methane be generated in the lower sediments, and if so how will it be vented so as not to damage the solidified sediments and the cap?
Potter writes: "The purpose of S/S is normally twofold: 1) to improve the structural stability of the material and 2) to reduce the leaching characteristics of the material to acceptable criteria." However, he goes to say: "The tar ponds sediments meet the leachate criteria even before the application of the S/S technology."
So the main objective of S/S then becomes improving the structural stability of the sludge and increasing the bearing capacity to allow a stable working surface for final grading and future use. The technology demonstration reported that the S/S process improved the handleability of the sediment, while its bearing capacity was relatively low. Will this processed sediment, with its low bearing capacity, be able to achieve the main objective?
Potter says the tar ponds sediments tend to have low leachability characteristics, meeting the leachate criteria even before the application of the S/S technology. However, the technology demonstration report states that while the samples used in this demonstration "represent a range of the type of sediments that exist, it is not conclusive that all the sediments in the ponds will behave the same." In addition, it is noted that all sediment samples used during the demonstration came from the South Pond; none came from the North Pond.
The only way to ensure all the contaminated soil mixes with the binding material (Portland cement) is to excavate the sludge and then mix it above ground, which is how it was dealt with during the demonstration and how it was proposed to be dealt with for full-scale treatment (the big "cleanup").
However, this is not what government plans to do. It plans to conduct the S/S process in place, leaving the sludge in the tar ponds while an attempt is made to mix it with Portland cement powder. How will that affect the outcome and how effective has in-situ S/S treatments proved to be in other full-scale, 580,000 tonne projects?
The fact that Potter says the project expects "to gain experience from the S/S work that will be undertaken on the cooling pond" doesn't inspire a lot of confidence. It seems there are more questions than answers.
Why did government waste millions of dollars and several years conducting a technology demonstration and then disregard the results? Area residents clearly chose removal and destruction technologies as the most acceptable options during the JAG, workbook sessions. Why ask their opinion and then ignore their chosen option?
It's a sad day when after 20 years of studies and millions upon millions of wasted taxpayers' dollars, the best government can come up with is to add some cement to the tar ponds, increasing the volume, and have our children and their children's children monitor it and maintain it indefinitely.
Marlene Kane, a volunteer advocate on
environmental issues, lives in Sydney.