The owners of a leaking uranium mine west of Denver have begun a bold project to reduce contamination of a creek that flows into a metro drinking-water reservoir: physically rerouting the creek so that it no longer flows over toxic waste.

Nobody wants Cotter Corp.’s re-routing of Ralston Creek to be permanent.

Federal biologists say the pine-studded creek corridor through a picturesque canyon is habitat for the endangered Preble’s Jumping Mouse.

But government permits were issued because the latest data show uranium levels between 40 and 50 parts per billion — above the 30 ppb limit — in water destined for 1.3 million metro residents.

Cotter work crews on Monday were completing a 21-foot-deep concrete-and-steel structure designed to channel all surface and shallow groundwater through an 18-inch-diameter black plastic pipeline running 4,000 feet around the Schwartzwalder Mine, once the nation’s largest underground uranium mine. As a condition of its 10-year federal permit, Cotter must irrigate the creek corridor to ensure that trees and wildlife survive.

“This is a temporary bypass that will allow us to do the permanent fix,” Cotter vice president John Hamrick said. “We really are trying to do the right thing here.”

This is happening amid a continuing and costly legal standoff between Cotter, a Denver-based subsidiary of defense contractor General Atomics, and state regulators charged with protecting Colorado’s environment.

Cotter also has agreed to use excavators and seven sump pumps to remove uranium from contaminated groundwater near the mine’s 2,000-foot-deep shaft, where uranium levels top 24,000 ppb. The sump pumping and subsequent treatment of contaminated groundwater over the past 18 months has removed about 1 ton of uranium that otherwise could have flowed into metro drinking water. That uranium sits in a guarded facility here until it can be trucked to a radioactive-waste dump.

Dealing with Cotter’s defunct Schwartzwalder mine has become a top priority for state mining regulators. Cotter still owns the mine, and a surety bond of $2.8 million is meant to ensure an eventual cleanup.

“We have got to think long term about how to get this site remediated,” said Loretta Pineda, director of Colorado’s Division of Reclamation, Mining and Safety.

State mining-board members have focused on the source of the uranium — the mine shaft — and repeatedly ordered Cotter to drain the mine and then remove the uranium from water. They’ve imposed $94,000 in fines, so far, for failure to comply with state orders. Cotter is challenging these actions in court.

“We have got several things in play for this spring and summer for Cotter,” Pineda said. “We will just see if we can move forward with those.”

State mining inspectors say uranium-laced water inside the mine shaft “is finding other ways out of the mine pool” and into groundwater and the creek beyond the mine.

“The only way to fix that,” Pineda said, “is to draw down the mine pool and treat it.”

Cotter favors a different approach.

While Hamrick acknowledged there may be some underground pathways between the mine shaft and Ralston Creek, he and Cotter health physicist Randy Whicker on Monday said pumping toxic water out of the mine makes no sense.

Such a project would require construction of a large plastic-lined waste pond, with the cost likely to exceed $10 million, and perpetual pumping of groundwater that would continue to fill up the mine shaft and turn toxic through contact with exposed minerals.

Better, Cotter contends, would be to keep the super-toxic water inside the mine shaft and treat it in there. Mixing molasses and alcohol into uranium-laced water would cause bacteria already present inside the mine shaft to multiply, Hamrick and Whicker said. These bacteria would bond with uranium particles, separating uranium from water so that it could settle deep underground.

“If you are knocking down the contaminants in the mine pool, who cares if the water gets out?” Whicker said.

Building a big plastic-lined waste pond would ruin the picturesque canyon, they said, create new environmental risks and delay restoration of Ralston Creek.

Colorado’s Department of Public Health and Environment also has a role to play here as the agency charged with protecting the quality of water. CDPHE inspectors on Monday checked out the concrete structure.

Denver Water officials are monitoring the situation.

Drinking water in Denver, Arvada and other areas that rely on Ralston Reservoir remains safe, utility spokeswoman Stacy Chesney said, because Denver Water’s treatment systems adequately remove uranium.

“The pipeline is an adequate short-term fix, but we want to see Cotter pursue the long-term solution, which is cleaning up the mine pool,” Chesney said.

“We continue to be concerned about this issue and want Cotter to do the responsible thing and clean up its mine,” she said. “We want Cotter to comply with all orders of the Colorado Mined Land Reclamation Board, which means de-watering the mine pool.”

Bruce Finley: 303-954-1700, twitter.com/finleybruce or bfinley@denverpost.com