From Greeley to California’s Central Valley, Western communities are reimagining groundwater use for a hotter, drier future — and learning tough lessons about resilience, risk and responsibility along the way.
The City of Greeley built a redundant water system that draws from four river basins, hoping that diversity would spare the city any single disaster. But in 2020, all four of those watersheds burned. The city was able to turn off intakes and make use of settling ponds to keep mud and ash out of the drinking water supply.
“It would have been a good time to have a reservoir underground,” says Kelen Dowdy, who was water resource planning manager then and still works as a water planning manager for the city. Now, Greeley is moving that way with its Terry Ranch Project, developing an underground water supply and storage project in an aquifer with an estimated 1.2 million acre-feet of water to support a population that’s expected
to double — to reach more than 260,000 people — between now and 2065.
But they’re taking the same ethos of resiliency to the Terry Ranch Project, developing guidelines to limit drawing down the aquifer by less than 20% of its current level and, crucially, planning injection wells for pumping treated surface water into what will essentially be an underground reservoir free of evaporative loss and shielded from wildfire.
“It provides a third place for us to pull water from in the event of a catastrophe,” Dowdy says.
The approach reflects a growing awareness among water managers in the West that groundwater resources once thought to be oceanic and impossible to overtap are, in fact, limited. In Greeley, where 25,000 acre-feet of annual use makes an aquifer with total storage of about 1.2 million acre-feet sound bottomless, water planners like Dowdy are aware that there is actually a bottom. Groundwater still makes a critical addition to the supply, but communities are rethinking how and where it fits and exploring models to balance use with preservation. Robust data collection is crucial, but so is understanding that management choices are as much social and political as scientific.
Sustaining Groundwater
The City of Greeley initially sought to expand Milton Seaman Reservoir on the North Fork of the Cache la Poudre River, but federal agencies required a search for less environmentally damaging options. The Terry Ranch aquifer storage project rose to the top of the list. The first 16 wells that the city drilled into the aquifer will be used to characterize the supply, and assist in future monitoring for signs of aquifer depletion in the relatively less-tapped Upper Laramie aquifer underlying the project. The city’s water resource portfolio aims to be big enough to accommodate bold jumps, like the proposed West Greeley 300-acre multi-use development with a hockey arena and water park. Eventually, when population growth requires it, the aquifer will be used to store water from wet or average years to be recovered during dry years. City leaders have been adamant, Dowdy says, about using this aquifer sustainably and steering clear of the aquifer mining that has happened elsewhere in the state.
“The whole recharge component of [Terry Ranch] is to ensure that we’re really just depleting at a small percentage or not even depleting at all, over the long term, because we want to use this in perpetuity,” says Matt Sparacino, water resource planning manager for the City of Greeley.
While Greeley expects that recharge and careful monitoring will sustain groundwater levels in the Upper Laramie aquifer, other groundwater sources in the state are considered tributary and connected
to surface streams. One of the keys to sustainable groundwater use in Colorado, experts say, lies in acknowledging the interconnections between tributary groundwater and surface water — that if one is drained, the other suffers.
“Colorado figured this out — you’ve got surface water rights and then you have groundwater rights that are subordinate to surface water rights,” says Thomas Harter, a groundwater hydrology specialist with the University of California-Davis. Colorado and its water court system, he added, already know “how to deal with the most difficult part, which is the groundwater part that actually connects to the surface water.”
The Upper Yampa Water Conservancy District had drafted a plan to reflect that reality even before the Yampa River was officially designated as over-appropriated in 2021. Groundwater supply in the Yampa Valley represents less than 10% of total water use. Still, for property owners to add a second well for more than domestic use, like a garden or a second dwelling unit, they must augment that well with more surface water releases from reservoirs upstream. To address that need, the conservancy district created a blanket augmentation plan and fronted the legal costs, sparing individuals a lengthy and potentially expensive process for what often amounts to less than a single acre-foot of water per year. The plan, too, has spared the basin the tight administration seen in other regions in the state that have struggled with sustainable groundwater use, says Holly Kirkpatrick, public information and external affairs manager for the Upper Yampa Water Conservancy District.
“I think it’s important to look at our systems as a whole, really gaining that understanding that when you’re pumping groundwater, that really does affect the quantity of the water in the system as a whole,” Kirkpatrick says. “As we look toward a hotter, drier future and we look at the potential for population growth and further development, it’s really important that we understand that and make decisions that allow us to operate within our means in terms of water supply.”
Colorado learned some of these lessons the hard way: In 1985, Kansas filed an interstate lawsuit alleging that well-pumping in Colorado was depleting the Arkansas River in violation of that river compact. In 1995, the U.S. Supreme Court agreed. Wells were shut down, water pumping cut by a third, and Colorado was required to augment the water consumed by wells that continued to operate. The state also had to pay $34.5 million to Kansas for damages.
“The problem that got us out of compliance was not fully understanding and accounting for the relationship between groundwater and surface water use,” says Hannah Holm, Southwest region director of strategic projects and partnerships with the nonprofit American Rivers. Holm co-authored a white paper on Colorado’s experiences with interstate compacts. “That was pretty painful to rein in.”
As a result, the state has taken measures to require water rights allocations for groundwater use in tributary aquifers — those with clear hydrological links to the streams and rivers nearby. Plus, there’s now more, better groundwater data to support better planning.
But the way surface water and groundwater connect varies widely. Therefore, some waterways immediately change when groundwater nearby is drained, and others may take a century to reflect that depletion. Measuring exactly what’s going on underground can be tricky, Holm adds, and that uncertainty leaves a space where a community’s risk-tolerance level begins to play a role. Risk-averse assessments might want to err on the side of using lower estimates, even if those come at opportunity costs. Others might see benefit in taking higher estimates on what’s available and a more optimistic approach to use.
“It is really hard, reckoning with the limitations that exist, and also with the guesses, the uncertainty about what the future can hold,” says Kelsea Macilroy, a project manager with The Langdon Group and a social scientist with ongoing research in sustainable water use who co-authored that paper on compacts with Holm. “That makes it hard for people to embrace change and engage in some of those more proactive behaviors.”
That’s particularly true when proactive behaviors are painful, like cutting back on use at a well that’s flowing fine because nearby wells are running dry or reducing use when there’s plenty of water out of fears for a future in which there won’t be. She advocates for taking a more comprehensive view of groundwater management as more than just a plan for removing water from the ground, she says, “Because it touches on all aspects of peoples’ lives and livelihoods and wellbeing, and the future.”
Across the West
Throughout the West, people are reckoning with these coming changes and making tough choices as communities. Arizona has identified six areas, known as Arizona Active Management Areas, where heavy reliance on mined groundwater needed to be brought into check. Arizona’s lawmakers established those areas with the 1980 Groundwater Management Act — they include the state’s urban centers but few of its rural areas. Some of those management areas acknowledge a goal of preserving a primarily agricultural economy “for as long as feasible,” while contemplating the need, in the future, to preserve groundwater for non-farming uses. Others are searching for ways to import additional supplies. These active management areas are also using aquifer replenishment, in this case, treating wastewater to recharge aquifers. But outside those areas and places where the state has expressly restricted irrigated agriculture, no regulatory framework guides sustainable use of the state’s groundwater, which is both hugely important to its supply and tightly limited. More than 40% of demand in the state is supplied by groundwater, according to Arizona State University, and those aquifers filled over the course of thousands of years, so won’t soon naturally replenish.
In California, as groundwater wells ran dry, both the land and water began to show signs of overuse. Seawater started seeping into freshwater aquifers and the ground above them started to sink, particularly in the Central Valley, compromising roads, rail lines, and homes. California passed the Sustainable Groundwater Management Act in 2014 to halt overdraft of its aquifers. The state is working now on supporting local agencies in choosing ways to end that over-use that meets their circumstances, land use, water supplies, and desired economic outcomes in that community.
“For a lot of basins this is an absolutely new concept, something that hadn’t been done before,” says Paul Gosselin, deputy director for sustainable water management with the California Department of Water Resources. “People hadn’t imagined you’d be limiting groundwater use.”
Eliminating overdraft will take some time — a glide path before leveling off — he adds, as these agencies wrangle with, in some cases, enormous challenges crafting plans for more sustainable water use. During that time, wells could continue to run dry. More than a thousand homes are on private wells that are no longer operable. In the most over-drafted basins, he adds, there’s probably half a million to a million acres of land currently used for agriculture that will not have water in the future. That land might be repurposed with habitat restoration, or solar voltaic arrays. What he’s learned so far is to see data acquisition as important, but to also recognize that it’ll never feel like enough, and to center local control and local relationships.
“These are people’s lives, communities, so that engagement and empowerment for people at the local level to have a voice and chart a course on how they’re going to achieve groundwater sustainability is really important,” he says. “Getting this right is really about building good relationships and engagement.”
The overarching goal was to bring water law and policy to recognize the interdependence of groundwater and surface water resources, linked in the hydrologic cycle through which rainfall slowly seeps into the ground to supply aquifers. But California is also looking to speed up that process of moving rainwater into aquifers to ease or potentially end overdraft.
The hope is to stretch precipitation, which mostly falls between October and April but is most needed from April to October, and to take advantage of wet years and the handful of atmospheric river-in-fused storms so that moisture buffers the cuts otherwise expected in dry years. The empty spaces in drained aquifers, which are estimated at more than three-times the size of the reservoirs on-surface, could store enough water that some basins could fix their groundwater overdraft.
“Fundamentally, all water management in California and elsewhere is about fixing what I call the spatial and temporal disconnect, where the water actually becomes available as precipitation, and then where and when it’s used,” says Harter, with the University of California-Davis. Here, the hydrologic systems present a tougher challenge for California, where precipitation that falls can be a fraction of the annual average, then swing up to 300% of it, “so this really, really wide range, which Colorado doesn’t have.”
Independent journalist Elizabeth Miller has written about environmental issues around the American West for publications including The Washington Post, Scientific American, Outside, Backpacker and The Drake.
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