By now, you’re drinking water from C.C. Cragin Reservoir.
Call it an Independence Day gift for Rim Country, since the gush of 3,000 acre-feet annually will assure the region’s water independence in an increasingly water-short state.
Payson’s been eyeing that water for decades, ever since Phelps Dodge built the dam that created the 15,000 acre-foot reservoir on top of the Rim back in 1962. The mining company created the reservoir to have water to trade for the water it needed to run its mines in eastern Arizona. So it swapped water rights with the Salt River Project, which brought it within reach of Payson.
The town finally sweet talked Congress into approving its rights to water from the reservoir in 2007, but it took another decade to finally build the system of pumps and pipelines necessary to deliver the water to Payson taps.
And that demanded technical solutions to a host of vexing questions.
For starters, how do you mix mineral-free snowmelt with mineral-laden groundwater, without a water quality nightmare?
Then how do you stash perhaps 2,000 acre-feet of water underground each year for future use?
And finally, how can you use this gush of water to wash away old political conflicts, while securing the region’s future?
The chemistry of water
For starters, the system poses a major challenge in chemistry — mixing the almost mineral-free, “soft” snowmelt from the C.C. Cragin Reservoir atop the Rim with the mineral-laden, “hard” water pulled from Payson’s aquifer, which has encrusted all the pipes and valves in the whole system with calcium and other minerals.
When Tucson took delivery of water from the Central Arizona Project, sludge sputtered out of Tucson water pipes when the soft water from the river dissolved the calcium coating the pipes. The dreadful looking water caused a scandal — and years of expensive retrofitting.
“We don’t want to do a Tucson, that’s for sure,” said Tanner Henry, Payson Water Department manager.
The water first goes into what’s called a “flocculation basin,” where the plant operators add a chemical that makes all the little particles in the water clump together so they’re easier to remove. An electric charge then makes the clumps grow larger.
“Gordon Dimbat is the water quality engineer at the town and he’s making sure everything is functioning properly, really on the molecular level.”
From the flocculation basin, the water goes to a maze of tubes with microscopic holes. The tubes filter out everything over a certain size — perhaps .01 micron. This removes all the solids, leaving only pure water. After passing through the microfiltration tubes, the water goes through a series of filters using granulated activated carbon, which removes the byproducts from the earlier processing and all organic carbon.
Ironically, the next step adds back in minerals, with the injection of carbon dioxide.
“The water from C.C. Cragin is really soft. The pH is too high. So this brings it down a bit — adds a little hardness,” said Tanner.
Next the water goes to giant mixing tanks, before heading into the pumps and into the town’s existing water system. Setting things up for the new water required the town to put new connections between its existing, separate well fields, so for the nine months the water from the reservoir flows into town, every house and business can use the Cragin water.
The town had to go through an expensive and time-consuming process to get permission from the state Department of Water Quality to mingle reservoir water with an existing drinking water system.
“So we want to match the chemistry as closely as possible. We don’t want to break loose any formations in the pipes. Over the years, we’ll slowly transition to softer water. We don’t want to make the same mistake Tucson did. So maybe over a number of years we’ll dial back our chemical usage,” said Henry.
Storing Payson’s future water supply
And if that’s not enough, Payson also has an unusual, “perched granite” aquifer, which means the water underground is stashed in crushed and complicated layers of granite. Sometimes, water flows easily from well to well along faults in the granite. Sometimes, the water levels in one well remain completely independent of a nearby well. The town has 42 wells, 37 of them feeding water into the system. Six 400- to 1,000-foot-deep wells will inject C.C. Cragin water into the fractures of the “Payson Granite” underlying the town.
“We honestly don’t have any idea how that will really work because there’s no way to predict it, although we contracted with a hydrogeology firm — ATC — and we’ve conducted tests over 48 hours. But we’ve never had a plentiful supply of water where we could run them full tilt for a month.”
Most towns and cities draw water from layers of alluvial material — sand and gravel deposited over thousands or millions of years by rivers. Those loose, uncompressed layers hold and release water readily. But Payson has an entirely different situation, since the water’s trapped in much less porous layers of granite.
“We don’t know if the logic of an alluvial basin applies, that’s what makes it really difficult. Everyone else has always injected into an alluvial basin, so we had to get the state to agree to our monitoring protocol to make sure we’re not surfacing water and making it come out of the ground in places it hasn’t before.”
The water levels in the network of town wells dropped 70 or 100 feet in many places before the town imposed tough water restrictions, shortly before the recession. Well levels stabilized about 10 years ago, still far below historic levels.
During the nine months a year the pipeline runs, the town will get all its water from the pipeline.
Not only will the town stop pumping water from the water table during the period, the six injection wells will add something like 1,000 acre-feet to the existing underground supply.
The town will resume pumping groundwater during the winter, when snows shut down the pipeline on top of the Rim.
The town’s not sure whether the water put underground through the six injection wells will spread out and replenish the diminished levels in other wells throughout the system. It costs about $100,000 to turn a normal well into an injection well. This involves reversing the flow at the bottom of a well, so instead of pulling water in from the surrounding rock, it pushes water back out into the ground.
“The question is how do you control a valve 800 feet underground?”
The answer involves a $75,000, stainless steel valve in the bottom of each injection well. “Stainless steel valves are not widely used in other places, so we’re getting inquiries all the time. Obviously, everyone’s concerned about spending that kind of money. They want to see if it works. So far, they’ve been a great success.”
In the final part of this series on Cragin, we will look at the politics of wastewater and wells.
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