The new Phoenix groundwater model: What it means and what’s next
On June 1, 2023, the Arizona Department of Water Resources (“ADWR”) released a new groundwater model for the Phoenix Active Management Area (“AMA”) through ADWR’s Assured Water Supply (“AWS”) program. The model covers the Hassayampa and East and West Salt River Valley sub-basins of the AMA, which captures most of the Phoenix Metropolitan Area. The model projects that at the end of a 100-year projection period—in the year 2123—four percent (4%) of the total simulated groundwater demand in the sub-basins will be unmet.
What it Means:
Arizona’s Groundwater Code was created by the Groundwater Management Act Of 1980. This groundbreaking legislation is a critical milestone in Arizona’s long and continuous history of proactively measuring, regulating, and planning for its long-term water security, a tradition that pre-dates Arizona’s statehood in 1912. No other state has such a robust tradition. For example, California did not adopt a groundwater management code until 2014.
The new model from ADWR is part of the regular effort to monitor Arizona’s water resources. The results of this week’s study are not surprising to Arizona cities or long-term landowners, and merely remind us of the need to continue ongoing efforts to both conserve existing supplies and identify new supplies and technologies to maintain a secure water future for our State. It bears repeating: the newest study identifies an issue that will accumulate over the next century. Arizonans know that living in the desert requires serious forethought and long term preparation.
Arizona communities within the Phoenix AMA rely on a mixture of surface water (from rivers), groundwater (from wells), and reclaimed water (treated wastewater). For some, like the City of Phoenix, groundwater makes up only a small portion of overall water use because the City has access to surface water. Other communities, such as the newer communities on the outskirts of Phoenix, primarily rely on groundwater. That is a problem because groundwater is a finite resource—meaning that once it is used up, it is gone.
The model does not mean that Arizona is out of water. Instead, it is demonstrating that Arizona’s finite groundwater supplies have already been allocated to existing and approved developments. Arizona communities still have access to their surface and reclaimed water supplies. Furthermore, the groundwater allocated to existing and approved developments can be used as planned. The new model means that the Groundwater Code is working as intended, because the groundwater for these developments is assured. However, the model does mean that creating new developments that rely solely on groundwater has become more complicated.
Why it Matters:
A.R.S. § 45-576 requires developers of subdivided land to demonstrate that they have an assured water supply. Developers can do that either by obtaining a certificate under the AWS program, or obtaining a commitment of water service from a designated provider that has its own AWS designation. Most new development occurs outside of areas already served by existing designated providers. Acquiring surface or reclaimed water is prohibitively expensive, so most developers pursue certificates based on groundwater. Among other things, this process requires demonstrating that there is enough groundwater satisfy all the existing and new groundwater demands for 100 years.
One of the requirements to obtain a certificate based on groundwater is preparing a model to demonstrate that the water is physically available. Under A.A.C. R12-15-716, that model must demonstrate that over a 100-year projection period: (i) the depth to water does not exceed 1,000 ft below the surface, and (ii) the additional groundwater use will not cause unmet demand—which occurs when wells run dry in the model. The new model makes it impossible to demonstrate the physical availability of groundwater within the Hassayampa and East and West Salt River Valley sub-basins of the AMA. This effectively shuts off the issuance of new AWS certificates that are based on groundwater supplies within the model area.
What Happens Next:
New developments that have been issued a certificate, but which have not yet been built, are not affected by the new model. These developments may still move forward, and their water supply is assured. However, based on the new model, ADWR will not issue additional AWS certificates that are based on groundwater supplies within the model area. New development may still occur—it will just require careful and strategic planning.
In the short term, new development in the model area may still occur with the service areas of designated providers, such as the City of Phoenix. Those providers have their own designation of assured water supply, and uses within their service areas are already accounted for as part of the new model. Outside of those service areas, developers may scrutinize the model and argue that they can still demonstrate the physical availability of groundwater. The reported 4.86 million acre-feet of unmet demand value sounds large, but it makes up just four percent of the total projected groundwater demand. That is not an insurmountable deficit. Making reasonable adjustments to the model’s methodology could account for that unmet demand. These adjustments could include accounting for when approved developments will actually be built, considering the scheduled acquisition of new water sources, or providing for the deepening or relocation of wells with unmet demand. Such changes are realistic, and may lead to a more realistic projection of future conditions.
In the long term, the new model makes it even more important for Arizonans to consider augmenting our existing water supplies. Even before this model was released, communities in the Phoenix AMA were already pursuing new water sources to reduce their reliance on groundwater. Among other options, communities are already considering acquiring existing surface water rights through the severance and transfer process, capturing new surface water resources by improving infrastructure, and constructing additional wastewater treatment plants. Longer term solutions, like constructing desalination facilities or importing other new water sources, are also being discussed.
All of those augmentation options are viable, but they are complicated and will take time and resources to implement. As Arizona communities transition away from relying on groundwater, the State Legislature should consider thoughtful amendments to the Groundwater Code. It is possible to uphold the consumer protection aspects of the AWS program, while also fostering continued economic development.
Arizona has and will continue to be a national leader in water stewardship. Although this new model sounds alarming, the fact that we are proactively planning our groundwater use for the next 100 years is a good thing. Arizona has a water supply problem, but it is one that we can solve. Gammage & Burnham is proud to be on the forefront of this issue and our continuing work to implement creative solutions that benefit Arizona communities.