Copper World's proposed aquifer protection permit too weak, Pima County says

Arizona needs to strengthen aquifer-protection requirements for the massive proposed Copper World mine to guard against groundwater pollution beneath it, Pima County officials say.

The county officials say the Copper World proposal offers less protection for the aquifer than did the Rosemont Mine earlier proposed at the Santa Rita Mountains site southeast of Tucson.

“Under this current application, Hudbay proposes to use water to convey tailings in a slurry pipeline, operate an unlined tailings facility, leave waste rock dumps uncovered at closure, and deploy inadequate monitoring systems,” officials of three Pima County agencies wrote to state regulators.

“The planned processing facilities include a heap leach and other facilities that will process significant amounts of acid, and they will be located much closer to Tucson and Sahuarita’s municipal water supplies and rural domestic wells than was formerly the case.”

“Local communities deserve greater protection from pollution than is reflected in the draft permit conditions as currently written,” they told the Arizona Department of Environmental Quality.

ADEQ has proposed that the mining company, Hudbay Minerals Inc., be granted an Aquifer Protection Permit, which lays down the rules to protect against contamination. Pima County submitted 20 pages of highly detailed technical comments from the three county agencies and County Administrator Jan Lesher on the draft permit.

But Hudbay says not only does its project meet all industry standards, it will comply with all environmental laws. The state’s draft permit and supporting material accompanying it demonstrate that, Hudbay said.

The company also says its tailing seepage will be pure enough to meet drinking water standards.

“The statements that Pima County has submitted, along with those of other interested stakeholders, are contributing to a robust public comment period which both ADEQ and Hudbay have encouraged,” the company said in a written statement to Arizona Daily Star.

“Community’s water supply”

County officials want ADEQ to add tougher permit conditions, design requirements and review procedures if it approves the Aquifer Protection Permit.

The mine would operate on private land, largely on the west slope of the Santa Ritas, 28 miles southeast of Tucson and 12 miles southeast of Sahuarita.

The operation would also include the large open pit formerly proposed for the now-defunct Rosemont project on the mountains’ east slope — a facility now called the East Pit. It’s by far the largest and deepest of the six open pits planned.

The goal of a strengthened permit and tougher design requirements should be “to better ensure the design of this mine is more protective of the aquifer,” Lesher said in a note introducing the detailed comments.

In cases where ADEQ legally can’t require Hudbay to deploy industry standards to minimize pollution, the agency should encourage Hudbay to voluntary use such standards, county officials said. ADEQ’s “Best Available Demonstrated Control Technology” that it currently relies on in judging permit applications “is no longer the best available when it is outdated and less than industry standards,” the county said.

“Compromising the quality of our community’s water supply due to outdated standards in Arizona law in the name of reducing Hudbay’s costs is unacceptable,” Lesher wrote.

But while county officials say Copper World’s monitoring plan needs expanding, Toronto-based Hudbay says the project plan already meets ADEQ’s standard monitoring conditions for mines. The monitoring is aimed at detecting water contamination from a mine before it can seep too deeply into a neighboring aquifer.

The company’s steps will include installing monitoring wells to measure compliance with state groundwater quality standards around the mine’s perimeter, and management of various solutions from the mining process in processing ponds, the company said.

The draft permit requires more inspections than typically required for Arizona mine tailings facilities, the company said. Those include annual inspections of tailings disposal areas by an engineer and safety reviews of tailings dams by both an Independent Technical Review Board and an internal Tailings Review Board, Hudbay said.

But in criticizing Hudbay’s planned monitoring well network of 10 wells at the mine site’s edges, county officials noted that for Pima County’s sewage treatment plants, “ADEQ has required the county to have (monitoring) wells up to 7 miles downstream of discharge locations.”

The county also takes the mining company to task for omitting a highly innovative, although untried on a large scale, technology known as dry stack tailings. The dry stack method, which had been a prime feature of the previous Rosemont Mine proposal, would press and filter tailings to reduce water buildup that could potentially leak pollutants into the aquifer.

Dry stack tailings were heavily promoted for the Rosemont project that Hudbay and an earlier owner had proposed for the Santa Ritas’ east slope. Some environmentalists opposing that mine were skeptical of their feasibility.

Not only would the dry stack tailings be less likely to pollute the aquifer, they would use much less water, Rosemont’s proponents said during the 2010s.

“Pima County would like to return to Hudbay’s original design of dry stacked tailings as a demonstration of environmental stewardship,” county officials said in their comments on Copper World.

But Hudbay said limitations of available land on the west slope, topography and logistical challenges in processing and transporting make dry stack tailings not viable for the project’s first phase. That’s the phase covered in the draft ADEQ permit.

“Future phases may allow for the implementation of dry stack tailings, pending further study and additions to the land configuration. The current proposed tailings storage facility meets ADEQ standards and is consistent with industry practices for similar mines in Arizona,” Hudbay said.

Discharges from 16 facilities

The ADEQ permit would regulate discharges from 16 Copper World facilities including five of its six open pits. The East Pit is excluded, on the grounds that it’s considered a “hydraulic sink.”

Hudbay and ADEQ expect it will lose more water to evaporation than it will gain by groundwater seepage and rainfall runoff. So pollutants contained in the pit lake left from mining will stay, and not be discharged into the aquifer, they say.

Other facilities to be regulated by the permit include two mine tailings disposal areas, a large waste rock storage facility, and seven ponds used to capture stormwater and to store various solutions left from mineral processing.

Also covered would be a pad used for heap leaching. Hudbay proposed it in a preliminary economic assessment of the project in 2022, then dropped it when releasing a preliminary feasibility study last September.

Responding to the Star, Hudbay said, “Heap leaching remains an option for the project pending additional testing.

“It’s important to note that the (feasibility study) is not necessarily the final plan and industry practice typically involves updating mining plans and permits throughout development and operations to optimize projects.”

By far the largest permitted facility would be the waste rock storage area. That’s where most excavated rock with metal concentrations too low to be economically processed would be dumped, although the company would backfill three smaller open pits with waste rock, too.

The waste rock area could store up to 528 million tons although it’s currently planned to hold 477 million, ADEQ says. About 85% will come from the East Pit, the permit says.

Next largest would be two tailings disposal areas, with respective storage space of 231 million and 47 million tons. A primary settling pond will store any water reclaimed from the tailings areas. It will be up to 20 feet deep and cover a little more than five acres.

The draft permit says the mine operator “shall operate and maintain all permitted facilities to prevent unauthorized discharges,” as defined by state law, that would stem from the failure or bypassing of the site’s best available pollution control technologies.

Such discharges could result from liner failure, uncontrollable leakage exceeding the maximum storage capacity of a permitted impoundment, berm breaches that trigger unexpected fluid losses, and spills.

The permit says that unless otherwise specified, all required monitoring shall start during the first full monitoring period after the permit is issued, and last for the permit’s duration, regardless of the mine’s operating status. At the monitoring wells at the mine site’s perimeter, either eight monthly rounds or eight consecutive quarterly rounds of monitoring are required.

At the East Pit, which isn’t otherwise treated as a discharge facility, the mine operator shall develop a monitoring plan and maintain a monitoring well network, to verify that the pit is acting as a hydraulic “sink” to keep contaminants from flowing out, the permit says.

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Key concerns and responses

Pima County’s letter to ADEQ compiled a long list of specific concerns about the permit.

Here are some of the key concerns, with responses from Hudbay.

1. No tailings liner. Many of Copper World’s ponds and its possible heap leach pad would be underlain by plastic membrane liners to prevent pollutants from seeping into the aquifer. Tailings areas — officially called Tailings Storage Facilities — won’t have liners.

“The Tailings Storage Facilities have among the largest potential for aquifer pollution, and yet are prescribed among the least amount of protection,” the county said. “The (facilities) will be receiving tailings slurry that will inevitably produce seepage that will reach the aquifer, and it is unclear why ADEQ has approved a plan in which the tailings facilities and associated seepage collection system are not lined.”

ADEQ’s general standards for a Best Available Control Technology call for a tailings storage area to be lined with a 60 millimeter plastic liner atop a foot of compacted, native soil, the county said.

Lined tailings disposal areas would have less than a gallon per minute of seepage compared to 17.4 and 1,136 gallons per minute using two other storage plans without liners, the county said.

Responding, Hudbay said: “The Copper World Project fully complies with all ADEQ design standards and requirements to safeguard the aquifer. It is also consistent with other tailings facilities that have been recently permitted in Arizona.”

The ground’s geology underlying tailings areas function as a natural liner, allowing capture of 98% of all seepage through the tailings in “underdrains” and collection trenches built underneath them, Hudbay said.

Also, Hudbay says that in its application, “We have demonstrated to ADEQ that the tailings seepage water is expected to meet all Arizona Aquifer Quality Standards and even EPA’s Primary Drinking Water Standards. So the 2% of seepage that is not captured will not create groundwater quality issues.”

The underdrains will convey liquid that seeps through tailings to a lined impoundment, ADEQ said.

Also, ADEQ said it’s concerned about stability issues with a liner underneath tailings, because to ensure stability, tailings piles require consistent compaction of their materials that would be hard to insure with a plastic liner underneath. Consistent compaction will allow for appropriate drainage to engineered structures such as an impoundment, ADEQ says.

But these concerns are eliminated if the tailings would be filtered or pressed dry, as had been proposed for the Rosemont Mine, county officials said in reply.

ADEQ appeared to decide on a cheaper, less protective design for the tailings facilities “because of the perceived hardship on Hudbay that would be caused by construction of appropriate, protective facilities,” the county said.

“This is an unfair compromise between environmental protection and practicality,” county officials said.

2. Stormwater pond capacity. Runoff likely to be generated by a 100-year storm, on the scale of one expected to occur once in 100 years, will be a lot more than Hudbay projects, raising questions about the capacity of the mine’s main stormwater pond, the county says.

That pond has capacity to hold 18.8 acre-feet of runoff from the plant site during a 100-year storm lasting 24 hours, the draft permit says. But data from a nearby station shows that runoff from a 100-year storm over 24 hours is 42.5 acre-feet, the county says.

“Something is not adding up with this calculation and draft permit,” the county said.

Figuring out the pond’s capacity is not as simple as the county implies, Hudbay countered.

For example, the water in that pond can be pumped out and used in the mine’s processing plant, “so as it begins filling up with stormwater, we will begin pumping it out,” Hudbay said.

The capacity of the Process Area Stormwater Pond was determined through a complex water balance analysis and a Site Stormwater Management Plan, Hudbay added.

3. “Hydraulic sink.” County officials say the large East Pit should be regulated as a discharging facility despite statements by the company and ADEQ that it’s a “hydraulic sink” that will lose more water to evaporation than it takes in, eliminating the likelihood of discharge.

Because it will take time for the pit to act like a hydraulic sink, “there will be some period of time that the East Pit will be a discharging facility,” the county said. So monitoring wells must be installed in areas lying downstream of the pit to verify Hudbay’s claims about a hydraulic sink, the county said.

Hudbay hasn’t demonstrated that discharged pollutants in that area will be captured and hydrologically isolated in the depressed water table around the pit during early mine operations, the county said.

The county is wrong, Hudbay responded, in asserting the East Pit may not function as a hydraulic sink at first.

Before Hudbay begins excavating the pit, wells installed to “dewater” the area will pump out groundwater, lowering groundwater levels in the pit area.

“It is a basic hydraulic principle that groundwater does not travel upwards. Therefore, once dewatering begins, no water from the pit area will flow out into adjacent groundwater,” Hudbay said.

When mining stops, a pit lake will start to form because water will no longer be pumped out, the company said. That will establish a permanent hydraulic sink, Hudbay said.

“The pit’s design and our operating procedures will ensure effective containment and management of water throughout the project’s lifecycle,” Hudbay said.

4. Timing. The permit is premature because Hudbay hasn’t applied to the U.S. Bureau of Land Management for permission to build tailings pipelines across federal land and for rebuilding a tailings facility roadway across federal land, a project shown on Hudbay’s state permit applications, the county said.

While the State Land Department’s Board of Appeals has issued a separate right of way to allow pipelines to cross its land, it’s being challenged in court by opponents, and “it’s not clear if it’s legally valid for the pipelines,” the county said.

The county requested that “if a state permit is granted, the permit be contingent on receipt of all applicable federal and state permits.”

In response, Hudbay told the Star, “The State Land right-of-way is final and legally effective, eliminating the need for any BLM approvals. ADEQ’s APP (Aquifer Protection Permit) program focuses solely on protecting groundwater and does not include other permits or land use authorizations.”

5. Mine life. ADEQ’s draft permit says this will be a 15-year project, but the county says that phrasing is “intentionally and inappropriately misleading,” because the project’s total life could stretch 44 years.

That would happen if the company can someday procure the federal permits it will need to deposit some of its mine tailings on federal land, the county said, noting it was that issue that stopped the original Rosemont Mine from proceeding.

The permit’s actual term is valid “until it is suspended or revoked by ADEQ,” the county said.

A two-phased approach for a 44-year mine life, with a 15-year first phase, was presented in Hudbay’s 2022 Preliminary Economic Analysis (PEA) for the mine, the county said. But last year’s Copper World Preliminary Feasibility Study redesigned the project into a single, 20-year plan, the county said.

But because the company discussed a 15-year mine life in its state permit application, that indicates “their plan is once again for this Phase 1 and Phase 2 as presented in the PEA,” the county said.

“It is difficult to believe that Hudbay will do all this work, construct these facilities, and then leave the remaining ore body unmined,” the county said.

In response, the mining company said: “Hudbay has been clear that it intends to develop the Copper World Project, with the first phase starting on private land and requiring only state and local permits. With an investment of $1.7 billion allocated for Phase I construction, the project is anticipated to generate over 400 direct jobs and contribute hundreds of millions in tax revenues for Arizona communities.

“The project currently being permitted is constrained to the amount of private land that we have available for development.”