Don’t worry, the Rosemont Mine isn’t likely to pollute the well-loved Davidson Canyon or Cienega Creek southeast of Tucson, says the Arizona Department of Environmental Quality.

ADEQ has tentatively certified that the mine will meet state water-quality standards — with the final certification being a key approval needed for the mine’s construction.

Three other agencies, led by the Environmental Protection Agency, counter: Not so fast.

The EPA, the Arizona Game and Fish Department and the Pima County government have raised more than 20 written concerns challenging ADEQ’s findings. The EPA says the evidence indicates a “substantial risk” of violating state standards protecting fish, wildlife and habitat.

A final certification is needed for Rosemont Copper to get a Clean Water Act permit from the Army Corps of Engineers to dredge and fill several streams lying upstream of Davidson and Cienega. The EPA has veto power over the Corps permit.

At issue is whether the state has evidence to prove the creeks won’t be polluted, and whether it’s requiring enough measures soon enough from Rosemont Copper to prevent and mitigate pollution.

ADEQ says that as long as Rosemont Copper follows a long list of conditions and mitigation measures, it shouldn’t degrade Davidson or Cienega’s water quality, or cause pollution exceeding state surface-water quality standards at four tributaries — Barrel, McCleary, Scholefield and Wasp canyons — in or near the Santa Rita Mountains.

ADEQ says it doesn’t expect toxic materials in Rosemont’s dry stack tailings to seep into groundwater or into Barrel Canyon. It says Rosemont will build sediment-control structures to prevent large amounts of stormwater from flooding downstream canyons, causing erosion and water-quality problems.

To ensure compliance, the state will require Rosemont to find other water sources to replace a 17.2 percent expected reduction in flows into Davidson Canyon due to the mine after the mine is closed. These measures could include buying, retiring or transferring others’ water rights. The company must submit such plans 180 days after the Army Corps issues its Clean Water Act permit.

But the state should require Rosemont’s mitigation plan before, not after, approving the certification, said EPA and Army Corps officials.

Overall, ADEQ relies too much on plans for corrective action if pollution occurs and not enough on prevention, wrote Jane Diamond, water division director in the EPA’s San Francisco regional office, in an April 7 letter. The mitigations depend on various government-administrative actions that aren’t certain to occur, EPA said, so “EPA does not believe these activities may be relied upon” to prevent the creeks from being degraded, the agency said.

Game and Fish, while not predicting the mine will pollute water, cites several studies done for the U.S. Forest Service and Rosemont that raise the possibility of pollution. In his comments, Game and Fish assistant director Jim DeVos challenged the adequacy of much of ADEQ’s data and warned that the mine’s sediment-control facilities won’t hold up in big storms. He recommended much more detailed reviews by ADEQ of the potential for pollution by tailings, waste rock, heavy metals and copper oxide.

Rosemont Copper Vice President Kathy Arnold said the company expects a final ADEQ certification. The fact that ADEQ’s Rosemont groundwater and air-quality permits have survived opponents’ administrative appeals testifies to the department’s thorougness and thoughtful evaluation, Arnold said, and this case is another example.

“Many of the conditions in the ADEQ permits have more stringent conditions for Rosemont Copper than at other operations,” said Arnold, Rosemont’s vice president for environmental and regulatory affairs, in a written statement.

Lying amidst deserts and grasslands, Davidson and Cienega have been the centerpiece of the controversy over the copper mine. While neither carries nearly as much water as they used to due to a decade of drought, both still have rich stands of cottonwoods, willows and mesquites. The state classifies three miles of Davidson and 28 miles of Cienega as outstanding waters that can’t legally be degraded.

One issue is whether the mine could pollute them by discharging chemicals or other waste materials into tributary Barrel Canyon. A second is whether the mine will make pollution more likely by cutting off water flows into the creeks, reducing their potential for dilution.

A third is whether the mine’s activities will send too much sediment downstream, potentially smothering fish. Or whether stormwater will scour out the streambanks with flooding, leading to erosion which also isn’t good for fish and plant life.

ADEQ counters that seepage of pollution is not likely to occur into groundwater or surface water from the mine’s waste rock or tailings. Rock buttresses built around the tailings should prevent precipitation from infiltrating through them, and the waste rock can neutralize acids, ADEQ says.

Game and Fish says that Rosemont Copper’s own report shows the majority of water seepage from the dry stack tailings will flow into Barrel Canyon for 500 years. The department quoted the Rosemont environmental impact statement as saying that if tailings seepage does reach Barrel Canyon, levels of six heavy metals, including lead, cadmium and silver, would exceed surface-water quality standards, although the statement also predicts such seepage is unlikely.

Contact reporter Tony Davis at or 806-7746. Follow on Twitter @tonydavis987.