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Arizona's aquifers remain at risk from 'unsustainable' pumping
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Arizona's aquifers remain at risk from 'unsustainable' pumping

The goal of balancing the groundwater we pump with what we can replenish through natural and human forces is increasingly out of reach in Arizona, a new ASU study finds.

The goal of balancing the groundwater we pump with what we can replenish through natural and human forces is increasingly out of reach in Arizona, a new study finds.

The study raises a long list of concerns about the state’s ability to balance groundwater supplies with pumping. That balance is an idea commonly known as “safe yield” — and it’s the cornerstone of Arizona’s pioneering 1980 groundwater law.

Only the Tucson area will be at safe yield by 2025, when the law said safe yield is supposed to occur in much of urban and suburban Arizona.

It is not clear how safe yield will be reached in the Phoenix and Prescott areas and in Santa Cruz County, the study says. The law does not plan for Pinal County to reach safe yield.

But these aquifers would still be in jeopardy even with safe yield because Arizona continues on a path of unsustainable groundwater pumping, the study says. That pumping affects localized aquifers within broader groundwater basins.

“If Arizona is to prosper into the next century, our focus needs to turn to what is essential for our future — the preservation of our groundwater and our increasingly fragile aquifers.

“Our own survival is at stake,” says the study from Arizona State University’s Kyl Center for Water Policy.

All indications are that we will have more demand for groundwater as Colorado River supplies for the Central Arizona Project shrink because of climate change and increased development, said Sarah Porter, the Kyl Center’s director and one of the study’s co-authors. Arizona will move into deeper overpumping if steps to fix it are not taken soon, Porter said.

“It is not too late for a course correction,” the study says, “but that will require that Arizonans face the truth and make bold choices. It will also demand courageous leadership.”

Dropping, like Lake Mead

The report compares our aquifers to the “iconic images of the bathtub ring around Lake Mead, caused by falling water levels that have been viewed by millions around the country and the world.”

If aquifers were equally visible, rather than underground, “many of them would be showing similar signs of stress as groundwater levels fall, the aquifers collapse, land subsides, and minerals and pollutants concentrate in the diminished supply that is left,” the report says.

The study is titled “The Myth of Safe Yield,” said co-author Kathleen Ferris, a Kyl Center senior research fellow.

“We’ve been striving for it for 40 years. We can’t quite figure out what it means to be in safe yield. We’ve had changing numbers over the years, about how close we are, and how far we are,” Ferris said. “And even if we get there, what does it mean? We’re not saving all this groundwater. We’re not protecting all of our aquifers.”

Law gets some credit

Ferris’ history with the groundwater law dates to the late 1970s, when she was director of the Arizona Groundwater Management Commission, which developed the law’s earliest drafts.

Later, she sat next to then-Gov. Bruce Babbitt when he and the state’s warring water interest groups negotiated the compromises that made the 1980 law possible.

Then, in the 1980s, she was first chief counsel and then director of the Arizona Department of Water Resources.

The law established state active management areas to govern pumping in the Tucson, Phoenix and Prescott areas and in central Pinal County. A separate management area was established later for western Santa Cruz County.

Without the law, groundwater pumping over the last 40 years would have been far, far greater than what occurred, the study says.

“More land would have been cleared for farms, new high capacity wells would have been drilled for agricultural, municipal and industrial use, unrestrained by any limits, and the aquifers would be in critical condition,” it says.

Conservation requirements stemming from the law helped increase the efficiency of water use and and reduced demand. Local water agencies have invested billions of dollars in treatment plants for using surface water and reclaimed water.

Many large recharge basins have been built to store renewable Central Arizona Project supplies underground so they can be used later when shortages develop, the report notes.

What needs fixing

But Ferris and Porter singled out several ways overpumping continues.

One is the well-established practice in which municipal water users and private water companies pump one part of an urban aquifer while replenishing it — or paying someone else to replenish it — miles away.

This practice was legalized after the 1980 law passed, to allow development in areas lacking CAP water supplies, and to allow underground storage of CAP water and treated sewage effluent.

In much of suburban Tucson, pumping by water users with and without CAP supplies is done from SaddleBrooke on the north to Green Valley and Quail Creek on the south. The compensating recharge is done along Santa Cruz River and in the Avra Valley, far west of and in different groundwater sub-basins from the pumping.

In the Phoenix area, the law allows renewable supplies to be stored in the Hassayampa Basin far west of the city and allows pumping nearly 100 miles away in the East Salt River Valley from an aquifer that would never benefit from the stored water, the study says.

‘Assured supply’ issues

Another problem the study cites is that state law allows local governments and private parties operating in four of the five water management areas, including Tucson’s, to meet the 1980 requirement for a 100-year assured supply for new development when groundwater is pumped 1,000 feet deep.

Today, the assured water supply requirement “is becoming one of the biggest obstacles to sustainable groundwater use,” says the study.

The 1,000- to 1,100-foot limits are not based on any hydrological principle — they were picked because they were less than the 1,200-foot decline that was allowed before 1980, the researchers wrote.

The consequences of letting water levels fall that far “should be every bit as concerning as falling Lake Mead water levels,” the study says. “As Lake Mead’s water level falls, the supply of Colorado River water that can be delivered decreases accordingly.

Similarly, as groundwater levels decline, the availability of this resource for the future is severely reduced, “and like the over-allocated Colorado River, Arizona’s groundwater supplies are already over-committed in some areas,” the report says.

The 1980 law also allows massive “unreplenished” pumping by cities, farms and industries with existing groundwater rights dating back before the law’s passage, it says. Unlike new pumping authorized today, that pumping need never be compensated for by recharging CAP water into the aquifer.

From 2012 to 2016, these three users conducted 158,000 acre feet of unreplenished pumping in the Tucson area, and well over twice that in both Phoenix and Pinal County.

One cause of this is that the framers of the 1980 law assumed most future growth would occur on farmland, which would save water because homes use less than crops. Instead, new homes have principally replaced raw desert, the study says.

“Development on desert land does not result in one type of demand replacing another. It results in a new demand … resulting in significantly greater demands than originally assumed,” according to an ADWR report the new study cites.

The report said unreplenished pumping has been mentioned repeatedly in ADWR reports and management plans and discussed by advisory committees — with little action.

“It has been clear for at least 20 years that unreplenished pumping is the Achilles’ heel of the ability to reach safe-yield, but Arizona has been unwilling to take the steps needed to address this fundamental flaw in our formula to protect groundwater,” the study concludes. “Mined groundwater is lost to the AMA (Active Management Area) and water users forever.”

Contact Tony Davis at 520-349-0350 or Follow Davis on Twitter@tonydavis987.

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Federal officials say it's likely Lake Mead at the Nevada border will be low enough at the end of 2021 to trigger the first major cutback in CAP deliveries to the Arizona's parched midsection.

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