Upper Tenmile Superfund site near Helen still active after almost 20 years

Posted at 8:00 AM, May 29, 2018
and last updated 2018-05-29 10:00:28-04

It has been almost 20 years since the Upper Tenmile Creek Mining Area was declared a Superfund site.

The town of Rimini is located in the middle of the site and the majority of Helena gets drinking water from Tenmile Creek. 

Cleanup for the site was originally planned to conclude by 2012 but the site remains active today. The site contains about 150 mines and is 53 square miles in size.

Congress established the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), or as it is informally called Superfund, in 1980.

Superfund allows the Environmental Protection Agency (EPA) to clean up contaminated sites and forces the parties responsible for the contamination to either perform cleanups or reimburse the government for EPA-led cleanup work.

There are 28 federal Superfund sites in Montana, 25 of which are on the National Priorities List.

In 1999, the EPA declared the area a federal Superfund site when it was determined to be contaminated with lead, cadmium, zinc, and other heavy metals hazardous to human health.

Mining began in the Upper Tenmile Creek area during the 1870s and continued through the 1930s.

Most of the mines were small operations that mined either zinc, lead, copper, or gold. The waste rock from these mines would either be deposited near the mines or used as building material for the town of Rimini, MT.

Dick Sloane of the Montana Department of Environmental Quality (DEQ) said the original miners would not have known that what they were doing would still affect the area.

“The people that were up here were following standard practices of the time and they didn’t realize the long-term potential impacts,” said Sloane.

Because of this and the relatively small size of the mines, no viable responsible party was determined.

The Upper Tenmile area presents a couple of unique challenges for the cleanup efforts.

To address the roughly 600,000 cubic yards of mine waste material, tailings, mine rock, and sediment have been excavated from properties and transported to a repository on the Continental Divide.

Most of the Rimini household lawns have been replaced and water has been provided to residents.

Six passive acid mine drainage treatment systems have also been set up to address outflow of water from several mines.

The city of Helena has five diversions for Tenmile Creek located above the major mine sites to ensure the water they’re taking is not from contaminated areas.

At the Tenmile Water Treatment Plant, the water is treated for a laundry list of contaminants such as heavy metals, nitrates, and other contaminants before being ready for public consumption.

City of Helena Water Production Superintendent Jason Fladland said one issue is the zinc level for aquatic species.

“It’s a secondary standard for us but there is also an MCL for the wastewater treatment plant," said Fladland. “It meets drinking water standards but not aquatic life standards.”

While zinc is relatively non-toxic to humans, it can have a harsh impact on macroinvertebrates and fish species.

According to the DEQ, the estimated cost for upgrading the facility to meet the zinc effluent standards is in excess of $50 million.

DEQ hopes that in the future they can reduce the zinc leading in the Upper Tenmile watershed drinking water to reduce the treated wastewater zinc levels so that they meet compliance.

Fladland said Tenmile is a great source of drinking water above the Superfund site though.

“It has very low alkalinity, very low hardness. Very low issues associated with taste and odor as well” said Fladland.

As for what’s next for the Superfund site, that depends on when funds become available from the EPA. There is a high amount of competition for Superfund money across the country right now.

The immediate risk to the public has been addressed for the site, but there are still 12 significant acid mine drainage sites that need to be resolved.

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