Tar ponds cleanup plan undergoes some minor revisions

By Nancy King
Cape Breton Post
Wed., Nov. 28, 2007

SYDNEY - A component of the Sydney tar ponds cleanup plan is undergoing a significant design change, with the decision to abandon construction of a steel channel through the site.

The Sydney Tar Ponds Agency is now reviewing a recommendation by design engineer Earth Tech/CBCL to pump water flowing from two brooks around the tar ponds to isolate the area during solidification and stabilization work while constructing the channels in the hardened cement mixture. It is now considering the design recommendations and will soon decide how the project will proceed.

The initial design called for using steel sheet piling to construct the channel to build a new brook alignment, with water from the two brooks that pass through the ponds, the Wash Brook and the Coke Ovens Brook, flowing through it. The channel, which was expected to take about 18 months to complete, would manage water flow during the solidification and stabilization of the tar ponds and allow brook water to move freely to the harbour, and prevent flooding of surrounding communities.

Last winter, a drill rig collected core samples from both the north and south tar ponds to ensure officials knew such things as the height of the bedrock and the soil conditions. "When that information came back, it was more detailed information than what we had before," noted Frank Potter, CEO of the Sydney Tar Ponds Agency. "There were two issues that came up, one was that the bedrock was higher than we had seen in other bore holes that were randomly picked in the ponds and there was more of a sandy material down there than initially thought."

As a result, the design consultant had to change the style of the steel sheet piling to be used in the channel, to a more expensive material. But as they proceeded with the design work and determined the length and depth of material needed, it was discovered it would add significantly to the cost, placing it over budget, Potter said.

Instead, the consultant re-evaluated alternative options and recommended blocking off the two brooks and pumping water around the ponds while the solidification and stabilization proceeds. "The original approach would have had us spend 18 months building the brooks and then let the water flow through for the remaining six or so years," Potter said. "This way what we’ll do is simply just block it off and pump it. We don’t have to pump the whole amount all the time but we’ll pump it as we work in certain areas."

The change won’t have any impact on the overall timeline for the cleanup project, although the short term schedule will change because the pump around solution is actually quicker, he noted. Depending on weather conditions and other factors, solidification could begin next year, a bit ahead of schedule, Potter said. "We’re still dealing with the water, still moving it around, but instead of flowing the water through a newly constructed channel we’re going to physically pump it around the portions of the site that we’re working in," he said

As for whether the situation should have been foreseen, Potter said these sorts of projects begin with a concept and a limited amount of information and then go on to the detailed design stage to ensure they don’t encounter any surprises later on that would force them to change course midstream.

There have been some other small changes to other components of the cleanup effort as more detailed information was obtained, Potter added, such as deciding to construct a larger building than originally envisioned on Ferry Street to wash trucks and clean debris coming out of the tar ponds.