CASA GRANDE — The Arizona Department of Water Resources’ new Pinal groundwater model is fundamentally flawed when it comes to predicting agricultural use, according to one member of the Pinal AMA Groundwater Users Advisory Council.
GUAC member Scott Riggins made the comment part way through a presentation of the effect of agriculture on groundwater in the model by ADWR hydrologist Jeff Inwood.
Friday was the first time the Pinal Active Management Area council members got an official presentation on ADWR’s new Pinal groundwater model. The model, which ADWR has been working on since 2015, was made public in mid-October.
Looking at a projected spike in agricultural groundwater use after the county loses access to Central Arizona Project water from the Colorado River, Riggins asked if ADWR had taken into account the economics behind groundwater pumping in agriculture.
He pointed out that groundwater is an expensive resource for farmers. It is costly to pump groundwater and it is costly to dig wells deeper in order to reach water, he said. There is a point where it becomes too expensive to use groundwater on certain crops and farmers have to make the decision to switch to another crop or stop growing all together. That could drastically impact the amount of water the agricultural sector uses in the future.
Did ADWR take that into account when figuring out future groundwater use by the agricultural sector? Riggins asked Inwood.
Inwood said the department hadn’t figured those costs into the model. Determining when a well would have to be deepened or when a farmer might have to switch crops due to the rising cost of groundwater was too difficult to figure out in a model that covered this much territory and over this length (100 years) of time, Inwood said.
“Just because it’s hard to put in the model doesn’t mean that it shouldn’t be in the model,” Riggins said. “This model is seriously flawed because these costs are not included. I will assure you agriculture has a maximum cost of water. You can’t grow things at a loss forever.”
GUAC Vice Chairman David Snider pointed out that the mission of the Pinal Active Management Area was to manage agricultural groundwater use.
Inwood said the department would need more input from farmers and other agricultural businesses to include the costs and their effect on groundwater pumping in the model. The department and its staff would be more than willing to sit down with farmers to discuss the situation and include the information in the model, he said.
Inwood said the department did the best it could with the information it had.
“This is an incredible piece of reality that needs to be included in the model,” Riggins said.
Snider pointed out what may be another flaw in the model. He asked if ADWR had factored in growth in the county’s industrial sector. There are several new businesses, such as Lucid Motors, that are planning to move into the county over the next few years, he said.
Inwood said the model assumed that groundwater demand from the county’s industrial sector would remain the same over the next 100 years. The baseline for the industrial demand was based on the county’s industry in 2015.
It was hard to determine what might happen with industry in the county over the next 100 years, Inwood said. However, ADWR could factor in new industry that was known to be coming to the area in the next few years.
Snider said he understood the department’s problems with predicting the future growth of industry, but the department could incorporate some assumptions in its model.
“Sometimes I have trouble predicting the weather, but at least I can make a guess,” Snider said.
Riggins said he thought the department had over-estimated the amount of water that would be stored in long-term groundwater credit banks over the next 100 years.
He found it unlikely that farmers, water companies or industry would be storing groundwater if they didn’t have enough groundwater to pump for their crops or customers.
“There are some serious scientific flaws in this model,” Riggins said. If those flaws aren’t addressed, it will be very difficult to find a possible solution to the county’s groundwater supply problems, he said.
The council also heard a report on the fourth and fifth Pinal Management Plans from ADWR Management Plan Program Manager Natalie Mast.
The department is continuing to work on the fourth active management plan for Pinal County and plans to start work on the fifth plan in the new year. A first draft of the fourth plan is expected to be released in February.
GUAC Councilman William Collings asked if ADWR planned to give the council an update on what changes were going to be made to the plan before the draft was released.
Mast said the department had previously discussed the possible changes with the Pinal GUAC and there would probably not be any new changes added to the draft.
Riggins pointed out that the discussion of those possible changes had happened several months ago and that ADWR staff probably had some new information or possible suggestions on how to incorporate those changes into the fourth plan.
These changes could have a dramatic impact on groundwater users in the Pinal AMA, Riggins said.
“We need to know what those changes are before a draft is published,” he said. Otherwise, the discussion on how to implement the plan could get bogged down over the various changes.
AMA Director Einav Henenson said the department would try to put together a list of changes for the Pinal GUAC before the draft was released.