Construction on the John Hart Dam, slated to begin within the next four years, is expected to put the city’s drinking water at risk.
BC Hydro has told the City of Campbell River that its John Hart Dam Seismic Upgrade Project, which is set to get underway in 2021, will likely impact the water quality in John Hart Lake, where the city draws its drinking water from.
“This is anticipated to put the city’s filtration deferral at risk and unless mitigated, may also result in boil water advisories,” said Jennifer Peters, the city’s utilities manager, in a report to council.
Stephen Watson, spokesperson for BC Hydro, said in order to upgrade the 800-metre long concrete and earthfill dam so that it can withstand a one-in-10,000 year earthquake, construction crews will have to lower the water level in the John Hart Reservoir. Watson said Hydro hired a consultant last year to look at potential water quality issues associated with lowering the reservoir level over a period of years.
“The consultant’s assessment concluded that no matter how much the water level drawdown is, the water quality would at times exceed the one NTU requirement for domestic water supply,” he said. “Turbidity would get into the reservoir mainly through fluvial erosion from the various tributaries that enter the reservoir.”
Peters said that “repeated turbidity events in John Hart Lake and boil water advisories would put the city’s filtration deferral at risk.” The deferral system moves the water from the intake (at John Hart Lake) to the city’s UV and chlorine disinfection system.
Because of the risk, Hydro has formed an external Water Quality Technical Advisory Committee and has included the city, Island Health, First Nations and other stakeholders in the process.
The committee is working to come up with solutions.
“Now we are looking at the technical feasibility of a few mitigation options, with one of them potentially drawing water from the Ladore Dam or from the Lower Campbell Reservoir to feed into the city system while the construction work takes place,” Watson said, adding that, “investigative work is just beginning.”
Peters said mitigation options will “decrease the probability of boil water notices while the (John Hart) lake is at a lower level and is essential to minimize the impacts of the BC Hydro project on the community’s drinking water.”
Peters said all indications are that once the project is complete and the lake is returned to its normal level, water quality is expected to return to normal conditions.
Peters added, however, that water quality will likely have to be monitored for at least one year after those levels are restored, meaning that whatever mitigation measure is in place, it will have to remain until 2025.
Hydro is expected to review the mitigation options this fall.
“The protection of water quality for fish and domestic water supply has always been very high on our radar screen from the beginning of this project,” Watson said. “We share the city’s concern on the challenge of maintaining good water quality for the community water system while at the same time upgrading the John Hart Dam so an uncontrolled release of water from the reservoir does not occur after a major earthquake – we’ve been open about this with the community on the interim downstream risk until the dam is seismically upgraded.”
The John Hart Dam project is currently in the feasibility design stage. The work is aimed at ensuring the dam, which was built in 1947, is strong enough to withstand a one in 10,000 year earthquake.
Hydro intends to implement a significant upstream berm, as well as a passive spillway at the dam so that when reservoir levels rise, water will naturally free-spill over that area.
Note: The John Hart Dam project is a separate project from the currently under construction John Hart Generating Station Replacement Project.