The New Magma Irrigation and Drainage District, a 26,900-acre farming area in Pinal County between Queen Creek and Florence, is about to capture water from an unusual source.
Formed in 1965 to receive Colorado River water via the Central Arizona Project, the district will start getting an additional 2,500-gallons-a-minute of treated water from an old mine shaft near Superior beginning about April 1.
Participants believe it is the first instance of mine water being reused for agriculture in Arizona.
The water will be delivered through a 27-mile pipeline built by Resolution Copper Co. to the Queen Creek area. It will be mixed with larger amounts of CAP water and distributed to farmlands in the New Magma district at low cost to the farmers.
The old mine contains billions of gallons of groundwater that have seeped in over the past decade, and draining the shaft is necessary to develop the new underground Resolution copper mine, said officials of the mining company, a unit of British mining giant Rio Tinto PLC.
But use of the mine water has dug up controversy. A group called the Concerned Citizens and Retired Miners Coalition, which opposes the massive multi-billion-dollar Resolution mine in general, fears the water will be too contaminated for safe use by crops and animals.
“When that water is given to horses, cows, sheep, it eventually makes its way into the food chain,” said Sylvia Delgado-Barrett, a former mine worker in Superior and now a Queen Creek resident. “They are putting it through treatment, but it can’t be that clean if it has to be diluted with 10 parts of CAP water for every one part of mine water.”
She thinks a better use of the water would be in mining processes in the Globe area, where the land is already contaminated.
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Manuel Ortega, chairman of the coalition, is concerned that chemicals put in the water to treat it will damage the soil in the irrigation district. He said the effects of the treated water have not been studied sufficiently.
“Resolution doesn’t do studies,” he said. “They do whatever they want.”
He said Resolution originally planned to discharge the water into Queen Creek outside of Superior, but that plan was dropped after it was opposed by Boyce Thompson Arboretum officials who said the water could have killed plants and damaged the soil.
Delgado-Barrett and other coalition members have brought their concerns to the town councils in Queen Creek and Superior and to state legislators, but so far no one has taken an interest.
“Everyone seems to have signed on to this without asking questions,” Delgado-Barrett said.
But she said the coalition will continue to appeal to Congress to reject a federal land swap that Resolution needs to fully develop the new mine.
Officials of Resolution and the irrigation district insist the water is safe for crops.
The copper company will process the water at a modern treatment plant in Superior before sending it to Queen Creek, said Brad Ross, Resolution’s manager of infrastructure.
“The water starts out slightly acidic,” he said. “It has some metals. There is some copper and other small constituents. You mix it with lime at carefully regulated levels, which makes the water slightly basic. The metals adhere to the lime and fall to the bottom of the tank. You remove the solids, and what you have left is nice treated water.”
The water will then flow through the pipeline, which follows the route of the old Magma Railroad to Magma Junction southeast of Queen Creek. It will be deposited into the irrigation district’s canal system at one of the points where the district taps into the CAP canal, he said.
A water quality permit was not required because the fluid is considered naturally occurring groundwater, not wastewater from an industrial process, Ross said. Company officials said the effluent emerging from the treatment plant will meet state water quality standards in any event.
The company did have to obtain a permit from the Arizona Department of Water Resources to withdraw the groundwater, an aquifer-protection permit from the Arizona Department of Environmental Quality to allow sludge storage in an impoundment area lined with an impermeable barrier, and a special use permit from the U.S. Forest Service to allow construction of part of the pipeline through the Tonto National Forest.
Ross said the water will be continually tested for quality, as will the soil and plants.
The company anticipates the flooded mine will be drained in about two years. At that time, water will still be available for the irrigation district at a much lower rate to keep the shaft dry, Ross said.
Eventually, however, the groundwater will be needed for operation of the new mine, said Resolution President David Salisbury. The dried-out shaft will be used for ventilation and access to the mine, he said.
Resolution officials didn’t disclose the cost of the draining operation.
TAP WATER NOT IN PLANS
Bill Van Allen, general manager of the irrigation district, doesn’t believe the water quality will be a problem.
“A University of Arizona water specialist is working with us to make sure everything is high quality,” he said. “We have a blending plan and a testing plan, so we are thinking it’s going to be fine.”
He said none of the mine water will be used for tap water in homes within the district.
Farmers will pay about $20 per acre foot for the mine water, versus $33 for CAP water, so they’ll get an economic break, Van Allen said.
The consultant on the project, Jeffrey Silvertooth, head of the Department of Soil, Water and Environmental Science at the University of Arizona, said the mineral content of the treated mine water is not very different from the natural groundwater.
But he does slightly share critics’ worries about the treatment chemicals — specifically the use of soda ash to make the water less acidic.
That will increase the liquid’s sodium content, and too much sodium can cause the soil to become crusty and less able to accept water, he said.
Silvertooth said the soil will be watched closely to make sure the buildup isn’t excessive.
“From what I can see, it will be fine,” he said, adding that he considers the project an important recycling effort.
“We live in a water-short place ... We need to be innovative,” he said.