State's likely OK of Marana's assured water supply draws group's protest

The path appears clear for Marana to gain a continuation of the state’s designation that it has an assured, 100-year water supply, despite a local conservation group’s strenuous objection.

Such a determination by the Arizona Department of Water Resources would allow continued, rapid subdivision development, mostly relying on groundwater pumping, for another decade in Marana, long one of the state’s fastest-growing communities. It would allow population to more than double by then within Marana’s water service area to about 72,000 people, town officials say.

The department recently signaled it’s likely to approve the town’s application to modify its existing assured water supply designation, first granted in the 1990s, by declaring it “administratively complete” about a month ago.

That action came after 18 months of negotiations between ADWR and Marana to repair what the state had previously said were deficiencies in earlier versions of the town’s assured water supply plan.

This determination shows the state believes Marana is close to proving it meets seven criteria established in regulations for showing it has an assured supply. They include having a water supply that is physically, legally and continuously available and demonstrating the financial capability of providing it.

The state can’t make a decision, however, until after it gives the public until Jan. 22 to file formal objections to Marana’s request. Then comes a review period of up to 60 days for ADWR to determine if the application’s substance meets state requirements. If the department decides to hold a hearing on any objections, that would push a decision back 30 more days.

An objection has already been filed by the conservation group Tortolita Alliance.

It contends the proposed assured supply status relies way too much on groundwater and that projected declines in the area’s water table due to pumping are excessive.

Town officials, however, say the projected declines are actually unlikely to happen.

Marana’s total population was nearly 56,000 in July 2022, the most recent U.S. census report shows. But many of the existing residents live in parts of Marana that get water from the Tucson Water utility rather than from Marana Water.

Marana Mayor Ed Honea has predicted the town could reach a total population of 100,000 by the late 2020s. The regional Pima Association of Governments has projected slower growth, reaching about 78,300 people by 2035 and 86,000 people by 2040, but Marana officials say the town’s growth has often outstripped others’ projections.

Lowering the groundwater table

Marana’s application, from May 2022, said its computerized models found its groundwater pumping over the next decade will lower the area’s water table as deep as 800 feet, and drop 120 feet below current levels.

The 800-foot depth is 200 feet higher than the 1,000-foot-limit allowed under state regulations.

“The modeling results indicate that the regional aquifer contains sufficient groundwater to meet Marana’s projected demands,” plus other water demands in nearby areas for at least 100 years, said the town’s assured water supply application, written by the hydrologic consulting firm Montgomery and Associates.

On Friday, Marana Water Director Jing Luo said the current application has met all the state’s standards for showing an assured water supply.

“We will be working with ADWR to address every concern and objection received through their public process. Marana remains dedicated to proactive, transparent, and comprehensive water resource management,” Luo said.

The Tortolita Alliance says such a decline wouldn’t be healthy for the aquifer since native groundwater, once pumped out, is likely gone forever.

Such concerns are shared by some private hydrologists and university water researchers who have in the past told the Star they fear water level declines on similar scales could trigger subsidence, or sinking of the aquifer, reduce water quality and make pumping much more expensive.

But Marana officials say the groundwater pumped will be replenished by artificial recharge of renewable Colorado River water into the aquifer through nearby, manmade basins, and that the water table most likely won’t drop 800 feet. Recharge would be done by a regional water agency, known as the Central Arizona Groundwater Replenishment District.

Colorado River shortages

The Tortolita Alliance still objects to the application. Its president, Mark Johnson, says Marana’s ability to qualify for continued assured water supply designation illustrates what he sees as a major disconnect between some requirements of state water law and what he considers “prudent land and water supply planning.”

He is particularly concerned about officials’ ability to keep recharging Colorado River supplies into the aquifer due to the likelihood of future river water shortages.

His objection letter said Marana’s projected future population and water demands are “unrealistic and unsustainable.”

While a 1,000-foot reduction in groundwater levels is allowable under state law, he said it would still leave the aquifer “severely impacted with significant drawdown” in water levels 100 years from now compared to today’s.

“No evidence has been provided that indicates the (state-mandated) goal to attain safe yield has been achieved,” Johnson wrote. Safe yield means a balance between groundwater pumping and natural recharge.

A replenishment district spokeswoman, DeEtte Person, however, said the district is developing a “portfolio” of backup supplies it can use for recharging in case of shortages.

A local water expert, retired U.S. Bureau of Reclamation Engineer Eric Holler, said that as things stand today, the recharge planned by Marana officials should indeed be able to offset its pumping and prevent major water table declines.

“The purpose of the groundwater modeling … is to consider worst-case scenarios absent recharge and replenishment. We do not believe the water table in the area served by the town is very likely to drop to 800 feet deep, or in the vicinity thereof, due to the existing and proposed water usage by Marana Water customers,” said Marana Water’s Luo.

“We want to emphasize our dedication to preventing water level declines and maintaining safe yield. The Town is obligated to replenish for its groundwater usage. Our membership in the Central Arizona Groundwater Replenishment District (CAGRD) helps the Town fulfill its obligation to replenish the aquifer,” Luo wrote.

Shorter projection periods

One restriction the state has placed on Marana is in the number of years the town can project its future water demands and supply.

One reason is the uncertainty of future Colorado River supplies to the state, which could face deeper cuts, as soon as the end of 2026, than have already been approved.

Marana’s original application in 2022 had predicted its water demand and total available supplies by 2041. But in July 2023, ADWR told Marana Water officials it would no longer consider an application whose term stretches longer than 10 years.

The department has taken the same position for pending modifications and extensions of assured water supply designations for other municipal water providers, including in Tucson and the Phoenix area.

David McKay, manager of ADWR’s assured supply program, cited “revised projections and ongoing assessments for water availability in the state,” Marana Water Director Luo wrote in a follow-up letter to McKay on Aug. 4, 2023.

That caused Marana to change its application period to the years 2023 through 2032. That means Marana must go through this same process in a decade for its assured water supply status to continue.

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Concerns about groundwater use

Marana’s reliance on groundwater as an assured supply comes as the use of groundwater to support growth is coming under question elsewhere.

Its assured water supply application from May 2022 notes, “The focus of this analysis for Marana is groundwater from the regional … aquifer.”

While Marana will use some of its renewable supplies of Central Arizona Project water and sewage effluent by recharging that water and recovering it by pumping it later, “this analysis assumes projected demands are met via groundwater withdrawal. Continuous and physical availability of groundwater to Marana for 100 years is demonstrated” by a groundwater model, said the application from Montgomery and Associates.

Tucson, which has a far greater CAP supply than Marana, gets most of its drinking water from CAP water. The water is artificially recharged into the aquifer and pumped back out before it’s sent to customers for drinking.

In Pinal County, the state hasn’t authorized growth based on groundwater pumping since 2019, when an ADWR computer model found inadequate groundwater to support additional housing development.

In the Phoenix area, the state in June 2023 announced it would not certify any new subdivisions relying on groundwater as having an assured supply — although cities such as Phoenix, Goodyear and Peoria that have their own designations of assured supply can keep growing.

Probably the fiercest case against the use of groundwater to support new development was laid out in a 2021 report from water researchers at Arizona State University’s Kyl Center for Water Policy. Titled “The Myth of Safe Yield,” the report made a detailed and passionate case against allowing new growth based on groundwater.

In particular, the report criticized the state groundwater act’s provision allowing groundwater to be withdrawn as deep as 1,000 feet in the Tucson, Phoenix and Prescott areas and 1,100 feet in the Pinal County water management area.

“These numbers are not based on hydrological principles of the sustainable amount of groundwater that an aquifer can yield,” said the report from Kyl Center Director Sarah Porter and senior research fellow Kathleen Ferris, a former ADWR director and chief counsel.

“Rather, they are arbitrary numbers, picked because they are less than the 1,200-foot depth to groundwater that was permitted under the state’s 1973 ‘adequate’ water supply program, in which 1,200 feet was the deepest well in the state at the time,” the report said.

In his objection letter, Tortolita Alliance’s Johnson wrote that Marana’s proposed sources of water supply include 72% groundwater, 15% CAP water from the Colorado River, 12% treated sewage effluent and 1% coming from state-approved credits allowing a little more pumping based on water supplies previously artificially recharged into the aquifer.

Marana’s application “should not be approved until additional permanent and renewable sources of supply are secured,” he wrote.

But in a recent email to the Star about Marana’s application, Ferris wrote that while she has concerns about pumping at deep levels such as the town proposes, “it’s still within the depth allowed by the rules” from the state.

Johnson argued that any over-drafting carried out by Marana doesn’t meet the state’s goal of reaching a balance between groundwater pumping and recharge. But Ferris said that argument can’t be used as a legal grounds to deny Marana’s application for having an assured water supply.

“Marana’s groundwater use would be consistent with the management goal” because the town belongs to the Central Arizona Groundwater Replenishment District, she said.

Being in the district meets the management goal because the district is required to replenish its “excess” groundwater pumping, which is most of it, Ferris said.

Replenishing aquifers

Critics of the groundwater replenishment district’s practices have focused on cases — some of which occur elsewhere in Pima County — in which the district replenishes aquifers with CAP supplies in locations far from where groundwater for new subdivisions is pumped.

But that’s not what’s likely to occur with Marana’s pumping and replenishment, former Reclamation engineer Holler says.

That’s because groundwater replenishment for Marana will be carried out in two major recharge projects that lie within town limits. The recharge areas also lie within the same Avra Valley sub-basin that the town lies in, meaning the recharged water will likely prevent Marana’s pumping from seriously depleting its aquifers, Holler said.

“They will stop it from falling to 800 feet. They will have an impact,” Holler said.

The town’s wells lie within what’s called the “area of hydrologic influence” of the two recharge projects, he said. They’re known as the Lower Santa Cruz Recharge Project and the Avra Valley Recharge Project. Both are very near the Santa Cruz River.

Treated effluent flowing downriver from Pima County’s two big sewage treatment plants upstream of Marana will also help compensate for the pumping, he said. “It has been flowing down the Santa Cruz River for the last 40 years, somewhere around 68,000 acre-feet a year.”

The only thing Holler said he would question is the impacts to groundwater quality from the mixing of three water sources, effluent, CAP and native groundwater, in a single aquifer. Otherwise, “it all looks kosher to me.”

Getting credits for storing water

The replenishment district’s long-term recharge capabilities have come under question because of the likelihood of additional cuts in renewable CAP supplies due to continued and possibly worsening Colorado River shortages.

The district, commonly called CAGRD, operates under 10-year plans that show where its renewable supplies will come from for the following 20 years. Its current operating plan expires in 2025 and a new plan is being developed.

Tortolita Alliance’s Johnson mocks the state’s granting of assured water supply designations based on 20-year plans for replenishment.

“You are not guaranteed over the century that the actual water will be available,” he said. “If I came out and said ‘I just bought 100 years of water but we only got it for 25 years’, they would have laughed me out.”

Holler disagrees, saying anybody who tries to look out even 40 years in projecting future renewable supplies is “wacky.”

“But a rolling 20 yeas, in which you have to go out again and plan (for) another 20 years, that seems reasonable,” he said.

Person, the replenishment district spokeswoman, told the Star that while the existing district operating plan provides supplies for 20 years, the next plan “will demonstrate the CAGRD has sufficient water supplies to meet anticipated demands (for replenishment) over the subsequent 20 years and beyond.”

The district currently owns permanent rights or leases 100-year rights to recharge 27,000 acre-feet of CAP water statewide for a century and more than 33,000 acre-feet for 25 years, she said.

To prepare for CAP shortages, it has also obtained long-term storage credits to additional CAP supplies allowing use of more renewable water for recharge, she said. Such credits typically allow entities that own them the right to pump groundwater because they’ve recharged renewable supplies elsewhere.

In the Tucson region’s state-run water management area, the district has more than 150,000 acre-feet of such credits, plus another 41,000 acre-feet set aside in a reserve account. For comparison, the entire Tucson area’s annual replenishment obligation in 2022 was 2,750 acre-feet, Person said. That gives the district 60 years worth of replenishment water for the Tucson area based only on the 150,000 acre-feet of long-term credits.