By Kristine Edwards
When I first visited the Crystal Mine site (part of the Basin Mining Area Superfund Site in Jefferson County, Montana) back in 2006, I was so shocked by how bad it looked that I vowed to myself to get it cleaned up before I retired.
Acid mine drainage from old mines is a big problem in historic mining districts across the U.S. The pH of mine water at the Crystal Mine is around 2.7, which is pretty acidic (on a scale of 1-14, with 7 being neutral pH and what we like to see in uncontaminated water), and carries significant concentrations of heavy metals. In order to treat the drainage, we're working with our contractor on a treatment system.
An environmental contractor was working on mine sites in Peru when they came across a locally grown material that showed a lot of promise for treating acid mine drainage. It's called sugar cane bagasse, a byproduct of sugar cane. The bagasse is a light weight fibrous material. Additional research at the University of Colorado (Boulder) using sugar cane bagasse showed promise even at low pH levels and low temperatures. Since the Crystal Mine site is at 8,000 ft elevation, it can get very cold there in the winter.
Sugar cane bagasse sample
The bagasse is permeable and promotes biological activity by sulfate-reducing bacteria. This converts sulfate in the drainage to sulfide. Dissolved heavy metals like cadmium, copper, iron, lead, nickel, zinc combine with these sulfides to adhere to the fibers, leaving the water much cleaner.
We're running a treatability study at the Crystal Mine to see if the sugar cane bagasse works better at treating the drainage from this site than the typical methods. The manure and hay, a step in the process, are coming from a nearby barn and the aged wood chips and saw dust are from a local post and pole operation. So, even though the sugar cane bagasse is coming from Louisiana, we'll be using some local materials as well.
This will be a test that, if successful, could simplify treatment of acid mine drainage at other remote mine sites in this region. It would also lower maintenance costs, if it works the way we hope it will. The study will run from mid-June to October, and then it will take us about a month to interpret the results.
I hope to have a make a decision on how to clean up the site and the design plan in place by June 2015. The Superfund cleanup process can be long and it's taken several years to complete the investigation of the site. This treatability study with the sugar cane bagasse will help us design the final treatment system and could be something EPA or the state could use at other mine sites with acid mine drainage. I could then retire with a feeling of having accomplished my goal of cleaning up this site, and perhaps help clean up other sites as well!
Kristine Edwards at the Crystal Mine Adit Portal
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