Underground storage may be a key for Western states navigating water shortages and extreme weather.
Aquifers under the ground have served as a reliable source of water for years. During rainy years, the aquifers would fill up naturally, helping areas get by in the dry years.
But growing demand for water coupled with climate change has resulted in shortages as states pump out water from aquifers faster than they can be replenished.
Municipalities and researchers across the country are working on ways to more efficiently replenish emptied-out aquifers.
By overpumping aquifers “you’ve created space. There’s space under the ground that used to be filled with water,” explained Michael Kiparsky, water program director at the Center for Law, Energy & the Environment at the University of California, Berkeley School of Law.
“And what we can do with these groundwater recharge projects is take advantage of that space, which is vastly greater than the sum of all of the surface storage reservoirs that exist now or could be built,” he said.
Several communities across California, Arizona and other states have been using managed aquifer recharge for years to better regulate local water supplies.
If implemented on a wide enough scale, recharge projects hold the potential to bolster water security in drought-stricken regions while improving the health of the environment.
Kiparsky said if it can be pulled off, “it holds the promise of being able to generate a whole new water supply we really didn’t even know that we had.”
In California — where 85 percent of the population relies on groundwater for some portion of their supply — more than 340 recharge projects have already been proposed.
The California Department of Water Resources announced this month it will expedite the permitting process for recharge projects to help meet its goal of expanding average groundwater recharge by at least 500,000 acre-feet each year.
In Orange County alone, officials pump 65 million gallons of treated water into recharge basins in Anaheim each day. The county began recharging water through infiltration basins in 1936 and serves as a model for other communities looking to implement managed aquifer recharge projects.
“If we want to maintain our groundwater systems and sustain them, not deplete them, not mine the water, and we want to have enough water for everything else — for agriculture, for cities, for the environment, for the streams — so forth, we have to put a lot of water into the ground,” said Andrew Fisher, a professor of earth and planetary sciences at the University of California, Santa Cruz. “There is literally no choice if we do not do that.”
Groundwater recharge projects can take many different forms.
Communities could create percolation basins, where stormwater or excess river flows are collected in basins that are intentionally left open. Over time, water settles itself into the soil below and eventually into aquifers. Dry wells, which stop above the water table and allow water to percolate the rest of the way, can be constructed, along with injection wells, which lead water directly into aquifers.
Arizona has a long history of managed aquifer recharge efforts, thanks in part to the 1996 establishment of the Arizona Water Banking Authority (AWBA). Since its inception, the authority has used recharge to store nearly 5,600 million cubic meters of surface water from the Colorado River, as of 2019.
The number and capacity of recharge projects increased throughout Arizona during the early 2000s, with researchers crediting the project’s success to local political consensus, favorable hydrogeology and public funding, along with other factors.
“AWBA is an important example of how a strong regulatory framework, coupled with public institutions and funding can help support the adoption of [managed aquifer recharge] on a large scale, and how [managed aquifer recharge] can achieve broad water management and public policy objectives,” a 2021 Unesco report said of the practice.
The city of Tucson also serves as a model example thanks to its flexible approach to using renewable surface water supplies.
In 2018, the city stored and recovered 76 million cubic meters in the same year, while an additional 76 million cubic meters was stored for long-term use.
The city uses “soils as the treatment method for the surface water,” explained Sharon B. Megdal, director of the University of Arizona Water Resources Research Center in an interview with Changing America.
The surface water infiltrates into the aquifers and mixes with the existing groundwater, and then officials can pull out that blended mixed water to serve customers, she said.
Despite the established nature of Arizona’s programs, groundwater is still over pumped in some areas, and aquifer levels continue to decline.
“Arizona has quite an extensive history of utilizing managed aquifer recharge successfully, and yet there are still more opportunities,” said Megdal. “We don’t have all the answers. We still have lots to do. But from the basic point of what’s going on in managed aquifer recharge, we’ve done quite a lot successfully.”
When it comes to expanding the scope of recharge operations, “it’s very important that you have the right regulatory framework for it both for sufficient protections — because there are water quality implications, other types of implications — as well as predictability,” Megdal said.
One type of groundwater recharge project is called Flood-MAR, or flood-managed aquifer recharge. As part of this process, water managers could divert water accumulated in rivers during big flows to other areas, flooding land during the winter, or wet season, and farming the land in the summer.
“Part of the challenge for flood recharge is finding land that’s not already in use for other things, houses or fields. And finding areas where there’s enough infiltration capacity, which is a term of art that means where water can flow quickly underground and into the groundwater aquifers,” Kiparsky explained. Legal questions also come into play when projects aim to capture floodwater, as claims on downstream flows may already exist.
Additional challenges with recharge projects arise when water is collected in urban settings. Cities may not be located above opportune geological conditions for water to seep into aquifers. Groundwater in urban areas can also be contaminated with oil drippings or bits of tires from cars. Although this water can be treated before it’s put into the aquifer, treatment can be expensive.
For other projects, communities need to determine the best sites for recharge to mitigate the need for building new transfer infrastructure.
“In some cases, some of that stored water has to remain in the aquifer and can’t be pulled out later on,” said Megdal. That’s because groundwater is in motion, and communities may not be able to get back all the water they put in before it moves on.
Despite the many challenges unique to collecting different types of water at different times, through different means and in different areas, “there’s a lot of opportunity to implement [managed aquifer recharge] depending upon what water source you’re talking about, what ultimate use you’re talking about,” said Megdal.
“People are recognizing that we have to look at all sources of water and opportunities to make wise use of them,” added Megdal.
Not only can increased water storage help with water security in the future, but higher groundwater levels can also reconnect with streams, improving conditions for fish and vegetation along the stream’s corridor.
“We have and will continue to have too much water when we don’t want it and not enough when we do, and so storage is the key,” said Kiparsky.
“The fact that we’ve created this massive space underground holds the key to that problem,” added Kiparsky.