ADWR Releases Much-Anticipated Hassayampa Sub-Basin Groundwater Model

ADWR Releases Much-Anticipated Hassayampa Sub-Basin Groundwater Model

January 20, 2023
Alluvial aquifer in the Lower Hassayampa Sub-basin and small portion of West Salt River Valley (SRV) Sub-basin

Earlier this month, the Arizona Department of Water Resources released the Hassayampa Groundwater Model, a numerical basin-scale groundwater model that projects water usage by existing and planned development in an area west of the White Tank mountains and northwest of Phoenix.

The analysis finds a total unmet demand of 4.4 million acre-feet of groundwater over a 100-year period for the Hassayampa sub-basin. 

The projected unmet demand means ADWR cannot approve the development of subdivisions in the area that intend to rely on groundwater.  Multiple large master-planned communities, all of them subject to the Assured Water Supply program, are being proposed in the region. 

Arizona’s Assured Water Supply program is a critical element of its landmark groundwater-management laws.

An Assured Water Supply is one that meets certain prescribed criteria. 

The water supply must be physically, legally and continuously available for 100 years; it must meet water quality standards; the water supplier must demonstrate financial capability to construct the delivery system and related features; and, the water supply must be consistent with both the AMA’s explicit management plan and goals.

Depth to water in the model in 2116 ranges from less than 200 feet below land surface (bls) to over 1,200 ft bls

In 2021, the Department’s groundwater modelers found similar results in the Pinal Active Management Area

On June 28, 2021, ADWR presented an update of its modeling of groundwater conditions in the Pinal AMA to a group of area stakeholders. The results of that analysis showed that over a period of 100 years - 2016-2115 - unmet demand for groundwater supplies in the region exceeded 8 million acre-feet.

At that time, ADWR Director Tom Buschatzke informed the region’s stakeholders that in view of the modeling results, “the days of utilizing native groundwater for development in Pinal are over, it’s done.” 

He added that ADWR will not approve new assured water supply applications seeking to utilize groundwater within the existing Pinal model domain.

The Director’s conclusions this month regarding the results of the Hassayampa modeling were reminiscent of those observations following release of the Pinal model.

“ADWR previously worked with stakeholders in the West Valley that are subject to the Assured Water Supply program to seek solutions to the shortfall projected in the Hassayampa model,” he said on January 9.  

This graph shows the assigned demand in the historical and projection periods

“As Governor Hobbs signaled in her (January 9) State of the State speech, it is time to include legislators, the business community and all constituencies to address the challenges attendant to the Assured Water Supply program in the Hassayampa Basin and for all the water management challenges facing Arizona.”

In her January 9 State of the State address, Arizona Gov. Katie Hobbs announced the release of the Hassayampa model report and also launched the Governor’s Water Policy Council, which is dedicated to modernizing and expanding Arizona’s landmark 1980 Groundwater Management Act.

As in the Pinal AMA, identifying the challenges in the Hassayampa sub-basin – an area tabbed for considerable future development – is expected to enable important discussions about water supplies. 

As the Director indicated on January 9, those discussions may result in approvals of subdivisions subject to the Assured Water Supply program while maintaining the program’s vital consumer protection objectives.  

A slide presentation of the Hassayampa model’s findings, as well as ADWR’s report on the model, can be found here