7 Lessons in Groundwater Management from the Grand Canyon State

As California struggles through its fourth year of drought, it is worth remembering that other parts of the West are much drier than California and have been coping with water shortages for decades.  As the first state in the country to pass a comprehensive set of groundwater regulations in 1980, Arizona offers a potentially useful lens for its western neighbors managing increasing water demands and diminishing groundwater resources in an arid climate. 

Arizona’s Groundwater Management Act (GMA) took a centralized approach in establishing active management areas (AMAs) to protect groundwater resources.  AMAs cover 23% of the state’s land area but contain 80% of the state’s population, 50% of its total water use, and 70% of its groundwater overdraft.

Statutory requirements to control groundwater use in AMAs include prohibiting irrigation of new agricultural land, establishing a program of quantified groundwater rights and permits, developing a program whereby developers must demonstrate a 100-year assured water supply for new growth, requiring metering all wells pumping more than 35 gallons per minute, and mandating annual water withdrawal and use reporting.  Four of the five AMAs are managed to achieve safe yield by 2025.  Given that this is only 10 years away, what has Arizona learned so far?  What can California and other states learn from Arizona’s experience?

Here are seven lessons illustrating key successes, challenges, and questions in implementing Arizona’s groundwater program to date. 

1.  Assured Water Supply Program: Tying New Growth to Water Availability

One of the key successes of Arizona’s groundwater management is the Assured Water Supply (AWS) program for AMAs.  To comply, a developer must demonstrate a 100-year assured water supply for a new subdivision before recording plats or selling parcels (a subdivision is defined as six or more parcels with at least one parcel having an area less than 36 acres). A developer must be covered by a water provider whose service area includes the subdivision or otherwise prove that adequate quality water will be physically, legally, and continuously available to the subdivision for 100 years.  California has roughly parallel laws linking development to water supply availability in Senate Bills 610 and 221, but the threshold for the size of covered subdivisions is much higher (500 housing units instead of 6). 

Even Arizona’s far more demanding assured water supply program has had its challenges.  One such challenge is the prevalence of dispersed and smaller residential developments that do not trigger AWS requirements because they consist of fewer than six parcels.  Estimated groundwater withdrawal for these developments, which are primarily on small wells that are exempt from permitting, is believed to be substantial for the aquifers in some localized areas.   

2. Replenishment: Where’s the Water Going to Come From?

Renewable water supplies, such as surface water or reclaimed water, typically need to make up a majority of the assured water supply required for new residential growth in AMAs.  This has mostly been local surface water or Colorado River water from the Central Arizona Project (CAP).  Because many developers have no access to these water sources, the Arizona legislature created the Central Arizona Groundwater Replenishment District (CAGRD) to facilitate growth while meeting the AWS rules.  Developers or water districts can become members and pay a fee, and CAGRD will assume the developer’s responsibility for replenishing groundwater with renewable water supplies. 

The demand from developers for active replenishment under this program has been much greater than was expected, which leaves CAGRD with the question of where water for recharge or replenishment is going to come from, as the replenishment district has no permanent or assured source of recharge water. Most of CAGRD’s water has been purchased from CAP contractors who aren’t yet using their full allocation.  But with curtailments of Colorado River water expected soon and CAP contractors’ water demands rising, CAGRD will have an increasingly difficult time competing for renewable water supplies to meet its replenishment obligations.  One option is to pursue alternative renewable water supplies such as treated wastewater or stormwater for replenishment. 

Another issue is that where members withdraw groundwater and where infrastructure for replenishment is may be in different physical locations.  CAGRD’s statutory obligation is only to replenish within the AMA where groundwater withdrawals occur, which does not necessarily mean that the replenished water will be hydrologically connected to the pumping required for any specific development.  So in essence CAGRD membership offers no real assurance that there will be water physically available to serve a particular subdivision in the future.

Given that recharge will need to play a big part in California’s Sustainable Groundwater Management Act (SGMA), Arizona’s replenishment experience highlights the need to think now about where this recharge water will come from, how to diversify and secure sources to the extent possible, and ensure that recharge and pumping areas are hydrologically connected. 

3. Exempt Wells: They Add Up

Groundwater pumps with a maximum capacity of 35 gallons per minute or less are exempt from metering and reporting requirements in AMAs.  Such wells can be for domestic, stockwatering, commercial, and small industrial purposes.  Land subdivided into five or few parcels are not considered subdivisions and are not required to demonstrate assured water supply or replenish their groundwater withdrawals.  Exempt wells taken together are suspected of diminishing aquifers (including offsetting gains made in reducing overdraft), reducing river flows, and impacting riparian areas.

4. Metering, Reporting, and Enforcement:  Tools that work

Water users in AMAs with a pump capacity of 35 gallons per minute or greater are required to use measuring devices for wells and report this water use to the state annually.  This is valuable data for Arizona, and the state could not manage groundwater without it.  Having these water use databases is critical for monitoring aquifer conditions, planning, and tracking compliance.  In addition, the state has significant enforcement authority under GMA; violators of the Act can be fined up to $10,000 per day for illegal groundwater withdrawal. Although financial penalties are seldom collected, this authority provides significant incentive to comply with the Act.

California’s SGMA authorizes a range of groundwater management tools -- including mandatory well registration, mandatory measurement devices, pumping reports, and pumping fees -- that local groundwater sustainability agencies may elect to use.  Many agencies may choose not to use them, which means that statewide data availability will be far more limited than Arizona’s.   

5. Technical Modeling and Studies: Centralized Functions

The Arizona Department of Water Resources’ hydrology staff performs technical modeling and regional studies, including regional groundwater models for all of the AMAs.  Staff also assists in local planning activities relating to water availability, land use, and recharge planning.  ADWR’s centralized role in performing these functions offers a way to develop groundwater models and studies that can be more broadly agreed upon.  In California, for example, groundwater models are often a point of contention.  Different jurisdictions or management districts with overlapping authority may have different models for the same or connected aquifers.  In some adjudications and other disputes, opposing sides have hired separate consultants, creating a “dueling experts” dynamic that is costly in time and money. 

6. Surface Water and Groundwater Connection: Not Legally Recognized

Arizona’s surface water and groundwater is managed separately despite physical hydrological connections.  Surface water use is governed by the prior appropriation doctrine, while groundwater is subject to reasonable and beneficial use unless it is withdrawn in AMAs, in which case it is governed by quantified rights and permits.  The Santa Cruz AMA is one exception where its management goal – in addition to maintaining safe yield - also aims to prevent local water tables from experiencing long-term declines, which requires coordinated management of surface water and groundwater.

Surface water and groundwater are also regulated separately under California water law.  SGMA explicitly states that it does not affect or quantify water rights.  It does, however, allow for adverse impacts on local habitat and local streamflows to be considered in prioritizing groundwater basins.  Additionally, one of the “undesirable results” that must be avoided to achieve sustainability under SGMA is adverse impacts on beneficial uses of surface water.  

7. Safe Yield: What If It Isn’t Achieved?

Despite Arizona’s successes with many aspects of its GMA and related programs, the Prescott, Phoenix, and Tucson AMAs are not expected to achieve their safe yield goals by 2025.  There are many reasons for this, including loopholes, exemptions, and assumptions that didn’t pan out (e.g. anticipated conversion of agriculture to urban development).  If safe yield will not be achieved by the specified timeframe as originally planned, does this matter? What should be done about it?  What can help mitigate it?  This is not too early for California to ponder.  Consider that Arizona’s AMAs are struggling to achieve their safe yield goal despite a 45-year time horizon, while California’s groundwater agencies will have a more ambitious 25 years.  

Ultimately, unsustainable groundwater use could hamper future growth in Arizona as investors avoid the state for fear of inadequate water supplies.  Perhaps municipal bond ratings would be lowered to reflect long-term uncertainty about water availability and sufficiency.  These are possibilities not just for the Grand Canyon State but also for other regions with basins facing uncertain groundwater futures.