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Laura Seitz/Deseret News

Kennecott making seismic improvements to protect Magna highway

By Dennis Romboy  |  Posted Jun 3rd, 2016 @ 9:02pm


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MAGNA — Drivers on a stretch of state Route 201 in Magna likely don't know that a century's worth of Bingham Canyon Mine tailings formed the bluff paralleling the highway.

Rio Tinto Kennecott, though, is well aware of the estimated 2 billion tons of fine sand-like material, and what could happen to the slope along 1.8 miles of road in the event of a major earthquake.

Due to the water content, the company estimates the tailings could ooze across all four traffic lanes like paste, stopping just short of the Copper Club Golf Course and a cow pasture.

A recent study predicting a magnitude 6.7 earthquake or bigger shaking the Salt Lake Valley in the next 50 years accelerated Kennecott's efforts to stabilize the area. The company unveiled its $27 million plan Friday.

"It certainly raised our attention and it's not a risk we want to take, and so we're starting this project," said Paula Doughty, Kennecott manager for tailings and water services. "We want to get it where nothing will end up off Kennecott's property."

Since the mid 1990s, 46 dewatering wells and 1,500 wick drains — similar to a candle wick — have pulled 5 billion gallons of water out of the tailings over most of the 5,700-acre site. The water goes to a clarification canal where it is reused in mining operations.

Kennecott will now focus its attention on the toe of the hill next to the highway.

Starting next week, the company plans to install 12 dewatering wells and 22 monitoring wells to gauge how the new units are working over the next six to 12 months. It then intends to put in another 92 wells the year after that.

"Our goal is to draw down the water an additional 10 to 15 feet, and that is predicted to stabilize the slope," Doughty said. "Once we do that, this should be stable even if the big one hits."

Tailings from the Bingham Canyon mine have been piled outside Magna since 1906, reaching 230 feet high over what the company calls the south impoundment area. Kennecott stopped transporting tailings — the material left over after extracting precious metals from the ore that is crushed to the consistency of fine sand — to that site and started another impoundment area to the north in 1998.

Doughty said the pile grows 6 to 8 feet per year over the 3,300-acre north site, and its height will match the south area in 2029 or 2030. She described the tailings as "clean" and said they're comparable to Western soils.

Kennecott has reseeded the south area with native plants. Ranchers now run cattle and beekeepers maintain hives on the land.

Company spokesman Kyle Bennett said there are no plans to develop the property but the potential exists.

Contributing: Keith McCord

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