Has Tucson met its groundwater goal? Arizona officials don’t know

The state’s landmark 1980 Groundwater Management Act set the goal for the Tucson, Phoenix and Prescott areas to balance the amount of groundwater they pump with the amount of water they recharge by both natural and artificial means by 2025.

Today, Arizona Department of Water Resources officials can say for certain that the Tucson area had achieved that balance — a status commonly called safe yield — by 2019. But due in part to a variety of technical factors, they can’t say for certain whether this area remains in safe yield.

They also warn that future cuts in deliveries of renewable Colorado River supplies could push the area out of balance between pumping and recharge. Arizona's Colorado River allocation is being cut by nearly one-third in 2027, and additional cuts are likely if river flows continue to deteriorate.

A slide show ADWR presented at a public meeting in September said that as of 2019, the Tucson area was “at or around safe-yield. However, under Colorado River shortage conditions, it may be unlikely safe-yield is maintained.”

The uncertainty is a concern for several outside water researchers and experts who say it’s very important for the public to have the most updated information on groundwater pumping vs. replenishment. 

ADWR spokesman Doug MacEachern points out that the 2025 date was never a legally enforceable deadline. But it has loomed large in the eyes of experts and interested citizens for many years. It's a key benchmark for determining whether a region’s water use practices are on a path to being environmentally sustainable, said Val Little, who chairs a Groundwater Users Advisory Council.

“I want to know when we will know. It’s not good that we don’t know when. It’s important for us to know,” agreed Sharon Megdal, director of the University of Arizona’s Water Resources Research Center. “It could take time. They’re trying to do an awful lot,” Megdal said of ADWR. 

One reason for the time lag in determining safe yield status is turnover at ADWR as trained staff members regularly leave for higher-paying jobs with other agencies and the private sector. The experts who commented to the Star about the issue aren’t critical of ADWR, however — they say the Legislature doesn’t give the agency enough money to adequately carry out its duties.

But, Megdal said, “People do want to know where we stand ... and what they can do and should do."

Balancing water pumping and recharge has been seen as a way of preventing groundwater tables from declining, which in turn can stave off the risks that overpumping will lead to higher water costs and lower water quality as aquifer levels decline.

Perhaps most important, balancing pumping and recharge can ward off land subsidence, the collapsing of the earth due to depleted aquifers that often leads to earth fissures that can damage buildings, roads and other infrastructure.

ADWR officials know for certain that the Phoenix and Prescott areas haven’t met that goal, and have acknowledged they’re not likely to meet it.

The Tucson area's advanced water conservation practices and its adroit and intensive use of imported Colorado River water have gone farther than in Phoenix or Prescott towards bringing water use and recharge into balance.

While aquifer levels have declined significantly this century in unincorporated suburban areas such as Green Valley, Vail and SaddleBrooke, water levels have risen dramatically in much of the city of Tucson in the same period.

That’s because Tucson Water has replaced most of its pumped groundwater use with the use of Central Arizona Project water from the Colorado River. The water table has particularly risen in the city's central wellfield, located in its urban core and in midtown Tucson, and underneath the Santa Cruz River.

The area’s longtime over-pumping of groundwater — a practice commonly known as overdrafting — had halted starting about 2010, ADWR records show. Until then, the overdrafting of groundwater had been chronic both here and in the Phoenix area since about 1940.

But the department hasn’t been able to determine what’s happened to the balance between pumping and recharge since 2019 in what it calls the Tucson Active Management Area. One of eight such state-regulated water management areas, the Tucson AMA was set up by the 1980 law to regulate groundwater use while still allowing economic development and growth.

The state water agency has learned that groundwater demand in the Tucson area dropped 7% between the period 2015-19 and the period 2020-24, an ADWR slide shows. That decline was prompted mainly by farmers using 22% less groundwater over those years. 

Total water use in the region, including both groundwater and CAP water, has held steady in that time, rising only 3% between those two periods.

At the same time, ADWR's slide show indicates how dependent the region is on CAP water and, potentially, how vulnerable it could be to a major Colorado River shortage. CAP water accounts for more than 50% of the Tucson area's total supply mix from 2020 through 2024, the department says.

CAP's use here has increased 2% in that period. The use of treated sewage effluent has increased significantly in the same period, now representing 7% of the region's total water use.

But a key reason the state doesn’t know if we’re still in safe yield is that it hasn’t yet updated a groundwater computer model to help it make that determination. It’s scheduled to finish that task by the middle of 2027. But ADWR officials can’t say at this time how long it will take them to figure out if our pumping and recharge are still in balance.

That determination will have to be made by the modelers in conjunction with another ADWR office that oversees active management areas, Emily LoDolce, ADWR’s groundwater modeling section manager, said in a recent interview with the Star. 

“It’s impossible to speculate” when that determination can be made, added spokesman MacEachern.

One unknown at this time is how long the area must continuously be balancing pumping and recharge to meet the safe yield goal, LoDolce said.

Right now, “there’s no time frame associated with that. Is it a rolling average? Is it 10 years? Five  years? There’s no firm conclusion for the time period,” she said.

Just updating the groundwater model is a complex task by itself. ADWR has since the middle 1980s used modeling software produced by the U.S. Geological Survey to help it reach conclusions about safe yield, LoDolce said.

Every 10 years or so, there have been major upgrades to that software, “and there’s been quite a bit of software upgrading since 2013,” LoDolce said.

“The folks at the USGS as well as expert users of the software, they’re always figuring out ways to make the software match reality and run more efficiently,” she said. “We (also) have 13 years of data that the ADWR has collected (about water use and recharge) that we’ve incorporated into the calibration of the model. It’s going to have a longer period of record.”

But one key missing data point is the amount of water that has naturally recharged into the aquifer since 2019, through melting mountain snows or by streamflow through Tucson’s normally dry washes after big storms, ADWR officials said.

The agency has all the needed information about various trends in water use and in artificial recharge such as treated wastewater that flows down rivers. But for natural recharge, ADWR hasn’t yet aggregated all the information into its groundwater model, LoDolce said. 

As for staff turnover at ADWR, she said that’s “100%” a factor explaining why the safe yield calculation isn’t done yet.

“I’ve been here six years, and we’ve gone through three different teams of modelers,” she said. “Groundwater modelers are in high demand. Oftentimes they’ll go elsewhere for more money. I’ve seen this team change three times, and they don’t have to start from ground zero. We work really hard to document institutional knowledge. It’s not a gigantic setback, but there is a learning curve, a process of getting them up to speed so we can build up to the momentum that the previous team had."

MacEachern, who was present for LoDolce’s interview, added, “I think we have the best talent in hydrology right now that we’ve ever had. I think the talent is far less of an issue than it was in the early days of trying to determine what’s going on in each AMA."

But staff turnover's role in delaying a safe yield determination “is just so illustrative on how understaffed and underfunded the department is,” said Kathleen Ferris, a Phoenix-area water attorney and researcher who was an ADWR director in the mid-1980s.

“It’s really unfair to the state, to water management and to our citizens, to have such an underfunded agency that has this kind of importance in our lives and our future," she said. 

Sarah Porter, director of Arizona State University’s Kyl Center for Water Policy, said for many ADWR staffers, the department “is their wonderful training ground. They leave after 2-3 years to go to the Central Arizona Project or the Salt River Project or to the private sector. I don’t understand all the rules in state pay scales. But they’re trying to compete with agencies and places that can pay more.

“It is regrettable. It’s too bad,” said Porter.