In small doses, selenium is critical for life, but it’s deadly in high concentrations—and a big problem for watersheds with coal mines in their midst
Selenium, a naturally occurring element, has been a hot topic lately—and not for good reasons. Unearthed through surface mining practices, the metalloid can seep from waste rock into the groundwater and passing streams, poisoning life downstream, from algae to fish to birds, and entering the food chain at potentially deadly levels.
Teck Resources Ltd. has monitored selenium levels near its five coal mines in B.C.’s Elk Valley for years. Following a study in 2009, the mining giant decided to invest $80 million in a selenium water-treatment facility at its West Line Creek coal mine. Expected to be in operation by next spring, the facility will treat 7,500 cubic metres of wastewater a day, the equivalent of three Olympic-sized swimming pools.
The West Line Creek water-treatment facility is the first of six that Teck plans for the Elk Valley. Together they are part of a selenium management plan that will cost a projected $600 million over the next five years and $40 million to operate annually.
The plan includes water diversion and treatment, and research into improved selenium management.
Operating on a $5-million annual budget, the Line Creek plant will use a biological treatment process to clump the element into particulates, which can then be captured through a multi-step filtration process.
Teck has faced pressure from local environmental groups for years, and as it prepares to ramp up production at its mines in the Elk River Valley, improving selenium management is a must. The image above illustrates a key part of how it plans to do so.
1. A tank collects incoming water from West Line and Line creeks.
2. Water passes through reactor tanks containing sand, which organic matter attaches to and grows; selenium attaches itself to the organic matter and is separated from the sand. A carbon source is added, which combines with the organic matter. As a result, selenium is reduced to an insoluble form.
3. Selenium is separated and removed from the water.
4. Water is treated so it won’t decrease naturally occurring oxygen when it is returned to natural streams.
5. Sand filters remove any remaining solids.
6. Solids are thickened.
7. The remaining water is removed from solids.
8. Trucks takes the residual solids—organic matter and selenium—from the treatment process for permanent storage in a fully contained facility that is located in close proximity to the treatment facility. Water is returned to creeks.