Construction crews successfully completed an underwater rock blast night as part of the John Hart Generating Station replacement project.
BC Hydro contractor InPower BC performed the blast within the John Hart reservoir to remove a rock area and create an approach channel to the new water intake works at the John Hart Dam.
The blast took place at about 11:30 p.m. on Tuesday night, and was part of the scheduled work for the generation project.
“This is an important milestone and another potential project risk that has been overcome by our contractor,” says Stephen Watson, BC Hydro project spokesperson . “We’re pleased to see this event completed successfully with no impacts to the project, dam, nor to the City of Campbell River’s domestic water supply – the city draws water from the reservoir only a few hundred meters away from the blast area. It was very carefully carried out.”
“A lot of planning went into this blast event to ensure that it went successfully,” says Paul Sawyer, InPower BC CEO. “There were many facets to it, and from an external perspective, that also included engagement with government fish agencies, BC Parks and the City of Campbell River. It all went according to plan.”
Sawyer said that about 154 holes were drilled into the rock outcrop area for the placement of the packaged explosives. The specifications of the blast were to have very little ground vibrations, which was achieved.
Some of the planning for the blast included the timing, with the blast happening at night as this is the period when city domestic water withdrawals from the BC Hydro penstocks are lowest. Also, to nearly eliminate risk to the city water supply from potential turbidity issues and a resulting public boil water advisory, the John Hart Generating Station was temporarily shut down and all the downstream water flow was re-directed down Elk Falls Canyon. The closed off BC Hydro penstocks were kept full of water and became the short-term reservoir for the city water supply.
“The water release down Elk Falls Canyon went from 20 m3/s to 100 m3/s before the blast, and for a few hours after the blast, to draw any potentially turbid water away from the penstocks and toward the spillway section of the dam and down the canyon,” says Watson. “We then re-directed the water back through the generating station when it was known the turbidity in that area was compliant. It was operationally all completed before daylight.”
The Campbell River flows below the John Hart generating station remained unchanged at 100 m3/s to ensure spawning salmon were unaffected.
The double silt curtains are now back in place to protect water quality in the John Hart reservoir by separating the work area from the reservoir. InPower BC will now begin the process of removing about 3,000 cubic metres of loose rock from the reservoir bottom by crane and clam-bucket. The new rock approach channel allows water to enter the water intake works and the power tunnel down to the underground powerhouse.
The John Hart project remains on schedule for the new facility to be in full operation by fall 2018.
