Byline: Diane Dietz / The Register-Guard

MINING'S TOXIC LEGACY

Miners often trigger acid-water discharge when they unearth veins of sulfide-bearing rock, exposing them to air and water.

When mixed together, the three ingredients - sulfide rock, water and air - set off

Katrina Edwards, a Massachusetts researcher, describes it this way: "You've opened up a big tap of sulfuric acid and broken the handle. You can't stop it."

The sulfuric acid drops the pH of water to the regions of battery acid or vinegar. The Formosa mine in Douglas County produces waters with pH that low. Stick a shovel blade in the stream flowing from the mine entrance and in a week or two, it will be gone, dissolved away.

Because the acidic waters dissolve metal ores, they are rich in elements such as cadmium, copper, lead and zinc. Running into creeks, the metal-bearing waters kill bugs, fish and plants. Zinc is especially deadly.

Oregon has yet to complete a census of mine-related stream damage. Nationally, the tally is as high as 10,000 miles of streams on federal land alone.

Once started in a mine, acid drainage is difficult and expensive to treat. Researchers have tried plugging mines, running the tainted waters through cow manure-stocked treatment filters, and pumping chemicals into the waters to raise the pH levels.

One type of filter uses acid-tolerant bacteria that spark a chemical reaction that causes metals to fall out of the water solution. The bacteria are housed in containers of manure plus wood chips or sawdust, into which the acid waters are channeled.

"You can feed in water that's almost like battery acid, and you can almost meet drinking water standards coming out," said Jim Gusek, an engineer with the global environmental engineering firm Golder Associates.

But the filters can be impractical because of size and cost. If the acidic waters emerge from a mine at more than a trickle, the reactor may need to be acres in size.

Another strategy is to suck water out of the old mine shafts and pump in antacids such as lime or soda ash to raise the water's pH. That causes the metals to fall out and form a sludge.

The technique can be costly because it requires staff to remove the sludge, plus stringing electricity to remote sites.

The Formosa mine probably will need that type of treatment, said Greg Aitken, a cleanup manager for the state Department of Environmental Quality. A DEQ contractor estimates that a system would cost $6 million to build and $270,000 a year to run for the first 30 years.

A more controversial method is for the government to pay a mining company to re-excavate a leaky, acidic mine. The hope is that miners would remove enough of the sulfide to reduce the creation of acidic waters.