The decision on whether two dams at Colliery Dam Park will be removed, remediated or replaced now lies solely on the shoulders of city council with the completion of conceptual cost estimate reports and a peer review by a professional engineering firm.
Both reports were released Thursday.
The peer review, performed by Hatch Ltd., also considered several options put forward by representatives of the Colliery Dam Preservation Society and determined that the lowest cost option overall at $6.3 million, including 30 per cent contingencies, is the removal of both dams.
Rebuilding both dams is estimated at $11.2 million including contingencies while the estimate to replace only the lower dam is $9.5 million.
Estimates to rehabilitate both dams is $30.7 million while removing the middle dam and rehabilitating the lower dam is $17.5 million.
“We’re meeting with the city and we have a few questions regarding these numbers,” said Jeff Solomon, spokesman for the Colliery Dam Preservation Society, which organized to preserve the dams and the natural and social values of Colliery Dam Park. “The contingency costs, for one thing, could go either way. They could be 30 per cent more, but they could also be 30 per cent less. What they’re saying is they don’t really know what the numbers are. The numbers we’re seeing aren’t anywhere near as far off as we were concerned about as far as replacing the dams go.”
Solomon points out that the Hatch Ltd. report says, without contingencies, the estimate to replace both dams is $8.6 million while the removal of both dams is $5.5 million.
“That’s much closer than originally thought,” said Solomon.
Tom Hickey, general manager of community services, noted that when comparing estimates, capital costs and contingencies should be used. He also noted that rehabilitating the dams is considerably more expensive than replacement because of specialized techniques that would internally reinforce the dams with concrete, and widening the spillway which would require expensive rock removal along the spillway channel.
The firm of Klohn Crippen Berger was retained by the city to complete its own cost estimate review and perform the work last fall.
In October, when the issue originally surfaced after the provincial Dam Safety Branch deemed the dams a potential threat to human life, city council directed staff to commence with the removal of both dams and drainage of both lakes.
In December, after considerable public disapproval, council directed staff to carry out the peer review and conceptual cost estimates to establish potential alternatives.
Though the issue will go before council again on Monday (May 6) and once more on May 13, unless council changes its mind on its current direction no other motions will be voted on.
“It’s a bit of a dilemma for council,” said Mayor John Ruttan. “There are multiple choices to consider, all of them very expensive, so we’re going to have to see how council members look at this. Nine people will have a chance to speak on it and render their opinions.”
Council has allocated $7 million in the 2013 budget to do the work.
“Any options other than dam removal will have a huge financial impact,” added Ruttan.
The lower and middle colliery dams are 100 years old and were originally built as a means to wash coal.
Though the resulting lakes and trails have become a significant recreational area, engineering studies have concluded the dams pose a serious threat to neighbourhoods and schools downstream in the event of an earthquake or extreme precipitation event, most notably heavy rain on a deep blanket of snow.
Solomon said the Colliery Dam Preservation Society will meet with the city again to go over the new reports, and has scheduled a public meeting for 6 p.m. on May 10 at John Barsby Schoo Secondaryl to pass the new information on to interested residents.