Mactaquac dam life extension through full rebuild on site ruled out

A full section-by-section rebuild of the Mactaquac Generating Station in its current location is not a feasible option to extend the life of the dam beyond 2030, NB Power states in its latest update on the multi-billion Mactaquac project.

The Crown corporation must decide by the end of this year whether it wishes to build a new dam, complete with power generation, maintain the dam to keep the headpond but give up power generation at the site, or remove the dam and allow the river to return to its natural state.

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NB Power has also been exploring options to extend the life of the current dam beyond 2030, when it is projected to reach the end of its life due to a chemical reaction known as alkali aggregate reaction in its concrete. The chemical reaction has been taking place since the 1980s and causes the concrete in the spillway and powerhouse to swell.

In an update on its due diligence studies, NB Power said teams were looking at ways to extend the dam's life beyond 2030, perhaps even to the intended 100-year end-of-service date in 2068

"The full in situ rebuild, a section-by-section replacement of all concrete in its current location, was considered and was not found to be feasible," stated NB Power.

However, a partial rebuild of the current structure was determined to be worthy of evaluation.

"Under this approach, only some of the concrete around key mechanical components would be replaced," states the report. "The remainder would be left in place.

"Other civil and mechanical work would be performed to extend the life of the assets."

Another team is exploring possible ways to extend the dam's life beyond 2030 by putting more emphasis on the necessary interventions with mechanical equipment rather than with the dam's structure itself.

"As these two approaches evolve, it is possible that the two will converge into one as NB Power further assesses their potential benefits or drawbacks."

NB Power says if extending the life of the existing dam through such methods is found to be both technically and economically feasible, it will then compare that course of action to the three options that have been under study.

3 options

The three options that were initially put forward carry a cost of between $2 billion and $5 billion. Those options are:

Repowering the dam by constructing a new powerhouse, switchyard, fish passage facility and spillway. The existing concrete structures would be partially removed following construction. NB Power estimates the project would take 10 years to complete and require an average of 500 full-time employees during the construction period.

Retaining the headpond by replacing the spillways to maintain downstream flow control of water, and constructing a fish passage facility, but not allow for power generation. Existing concrete structures would be partially removed. NB Power estimates the construction project would take up to seven years and require an average equivalent of 300 full-time employees.

Restore the river by removing the powerhouse, main spillway and associated infrastructure, and decommission and remove the earthen dam. NB Power estimates that option would take four years to complete and require 150 full-time employees during construction.

Renewable energy

The Mactaquac station's generation capacity is 668 megawatts and NB Power notes in the report that any reduction in energy produced by Mactaquac must be replaced by other renewable energy, such as solar, wind, hydroelectric, ocean-power, biomass, biogas and sanitary landfill gas.

The provincial government requires NB Power to develop renewable energy resources to meet 40 per cent of in-province electricity sales by 2020.

"On average, Mactaquac produces approximately 1.6 terawatt-hours of energy per year, which would need to be replaced by equivalent, eligible renewable energy if the station is not rebuilt," states the report.