Blackfoot Bridge: A New Way to Mine

Blackfoot Bridge will be among the most environmentally advanced phosphate mines in North America. This mine will protect water quality, wildlife and vegetation in the area--while still delivering high-quality phosphorous, a key tool in global agriculture, and a necessity for feeding the world’s growing population.

What Makes Blackfoot Bridge Different?

We know residents of southeast Idaho are concerned about Blackfoot Bridge’s proximity to the Blackfoot River. We’ve thought about it, too. That’s why we are committed to and will put into place environmental safeguards that will protect the Blackfoot River from detectable increases in selenium.

Digging up and moving selenium-containing rock cannot be avoided when mining phosphate ore. Selenium is a trace mineral that is essential for good health, but is required only in small amounts. Too much selenium can produce a condition called selenosis. Selenosis is a rare, but potentially serious, condition in humans, animals and fish. That is why the Blackfoot Bridge Mine will include important safeguards to prevent selenium from mined rock running off the mining site.

Many sedimentary rock formations contain selenium, including those that surround phosphate rock in Soda Springs. When this rock is removed so we can reach the phosphate ore underneath, it must be moved and buried in overburden piles to allow for the beginning of ecological restoration, or reclamation. In traditional reclamation practices, this rock is buried under layers of clay, rock, topsoil and vegetation.

In recent years, selenium has been identified in streams and vegetation close to mining sites. This could happen when water from rain and snow seeps through the many layers of soil, rock and clay, passes through the mined selenium-containing rock and washes the material into the surrounding environment.

A New Way Forward

We’re committed to ensuring Blackfoot Bridge will be among the most environmentally advanced phosphate mines in North America—one that prevents selenium contamination in the nearby Blackfoot River and surrounding vegetation.

There are many different types of cover systems and liners that help prevent contamination of nearby streams and water sources. We have reviewed many options to ensure we meet our commitment to protect the Blackfoot River. As a result, we now think one of the best ways to do this is to use a laminated geosynthetic clay liner (GCL) over the selenium-containing rock.

Laminated GCLs consist of a layer of natural clay woven between two layers of synthetic cloth. They are used in many industries including agriculture, aquaculture, storm water retention and waste containment, among others. Because of their success in other industries, we believe laminated GCLs are the right way to go. But this will be the first time it’s widely used in a western phosphate mine, making Blackfoot Bridge an environmentally advanced mine unlike any others in the industry.

However, we’re not stopping there. On top of the laminated GCL, we’re also adding 18" of topsoil, 12" of subsoil/clay material and up to 6” of coarse sand/fine gravel as a drainage layer. These additional layers will provide a more traditional cover on top of the GCL, and with the added protection of the laminated GCL, the two cover systems can work together to offer a very high degree of protection for local water sources.

Using this laminated GCL cover system will limit water movement to the selenium-containing rock to a tiny fraction of what could otherwise occur. And stopping the water runoff from infiltrating the mined selenium-containing rock means the Blackfoot River is protected from any detectable increases of selenium.

The placement of topsoil, clay and a drainage layer on top of the GCL also will enable vegetation to grow on this land, allowing Blackfoot Bridge to undergo the same award-winning reclamation efforts as our previous mines. And we won’t wait until the entire mine is completed before restoring the land. Mine reclamation will begin as soon as possible after mining starts, which is typically within one to three years, and will continue while we’re mining. Once mining has ceased, our goal is always to restore the land to the highest possible standards.