Commuters driving to Salt Lake have come to accept enormous, man-made hills along I-80 as part of the landscape, but that landscape could look very different in the future if Kennecott Utah Copper's reclamation plans for the area come to fruition.
It may be hard to imagine now, but the massive, dry hills of dirt could someday be covered in native vegetation and provide a home for wildlife — although mining will have to end first for that to happen.
The 3,200 acres of dirt many Tooele Valley commuters see on their way to work are Kennecott's north tailings impoundment. Tailings are a byproduct of the ore mining process, in which large amounts of dirt must be taken out of the ground to yield a relatively small amount of usable metals. After rock is taken from the Bingham Canyon Mine, it goes through the Copperton Concentrator where it's ground down to a sand-like material. During this process, metals — primarily copper but also precious metals like gold — are extracted. After the rock is void of value, the leftover waste — tailings — are sent in slurry form through a 15-mile pipeline to the north tailings impoundment.
Kyle Bennett, communications and media relations specialist with Rio Tinto, Kennecott's parent company, said levels of metal concentrations found in the tailings aren't dangerous.
"With the exception of copper, the tailings are very similar to underlying native soils," he said.
Kennecott has already reclaimed its south tailings impoundment, adjacent to the north impoundment. The south impoundment was used from 1906 to 2001. In the late 1980s, seismic information about the stability of the impoundment revealed the 200-foot-high impoundment shouldn't be any higher because of the probability of a massive earthquake. So construction on the north impoundment began.
All of the south impoundment's 5,700 acres have been reclaimed with native vegetation and turned into wildlife habitat for animals like deer, coyotes and owls. The area has even provided seasonal grazing land for cattle.
"When we finish mining and we have no more tailings, we'll start reclaiming the north tailings impoundment," said Paula Doughty, manager of tailings and water services with Kennecott Utah Copper. Although there are no specific plans for development in that area, it is a possibility. Those plans will be determined closer to the time of closure. The same types of native grasses and shrubs planted on the south impoundment will also be used at the north impoundment when it is reclaimed.
Until that day comes, Kennecott will keep watering the tailings piles to keep dust down. It's difficult to quantify the amount of water used in this process, Bennett said, because the water used for dust control is the same water used to transport the tailings.
"We recycle a lot of that water back, and obviously there will be some loss," he said.
The tailings consist of two materials — one coarse and one fine. From the concentrator, the tailings come through two different cyclone stations where they are separated. The outer part of the impoundment is actually built with the coarse material and the interior is filled with the fine one.
To control the dust, the fine tailings — water-based slurry tailings — are distributed through spigots to dampen the outer edges of the impoundment as well as the interior. This is done through rotation every four days. In addition, a massive sprinkling system using recycled water is used to moisten portions of the impoundment.
The sprinkling system of recycled water is used as need dictates. A synthetic polymer mixed with water is also distributed from water trucks to control the dust on the outer slopes of the impoundment. Kennecott is currently looking at whether or not it's feasible to distribute the polymer through the sprinkling system.
Using recycled water is part of Kennecott's commitment to sustainability, said Bennett. That dedication to sustainability also carries over to Kennecott's Inland Sea Shorebird Reserve.
When the company was expanding the impoundment in the '90s, some wetlands were lost. As mitigation for the lost wetlands, Kennecott purchased 3,700 acres on the south shore of the Great Salt Lake and created the reserve, which serves 150,000 migratory and nesting shorebirds that visit each year, Bennett said. The reserve was recognized in 1999 as the Outstanding Environmental and Engineering Geologic Project by the Association of Engineering Geologists.
swest@tooeletranscript.com
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