Last winter, the state of Idaho succeeded in recharging 317,000 acre-feet of water into an important aquifer, enough to serve 700,000 homes for a year. It was an important milestone in an ambitious program to restore a groundwater source that had been overtapped for decades.

The water source is the Eastern Snake Plain Aquifer, a massive and complex groundwater source, which is also linked to springs that contribute to flows in the Snake River. A legal settlement among various water rights holders in 2015 compelled the state to begin replenishing the aquifer, which serves a variety of important constituents, including farms, cities and fish hatcheries.

With a large network of recharge facilities constructed already and more in the works, Idaho could be a model for other states struggling with groundwater depletion.

To learn more, Water Deeply talked to Brian Patton, executive officer of the Idaho Water Resource Board.

Water Deeply: Tell me about the Eastern Snake Plain Aquifer.

Brian Patton: It is a very large, very productive aquifer that underlies most of southern and eastern Idaho. It’s about 10,000 square miles in extent. It directly supplies water to about 1 million acres of irrigated land in addition to various cities, towns, businesses and industry in the region.

And it is hydrologically connected to the Snake River at various locations, so that springs flowing from the aquifer back to the river help augment river flows and thereby partially supply water for another 600,000 acres of irrigated agriculture.

Water Deeply: What’s the history of the aquifer?

Patton: Through the first half of the 20th century, we inadvertently added 17 million acre-feet of water to storage on that aquifer as a byproduct of building and operating irrigation canals across the plain. The irrigation canals leaked, so the water wasn’t lost. It went down into that aquifer. So we started tapping it for various uses in the late 1940s, and that accelerated through the 1950s and 1960s. By about 1990, 1 million acres of additional irrigated acreage had come online using that water supply.

Fast forward to the 1990s, and the aquifer had been dropping at an average rate of about 214,000 acre-feet annually since 1952. That added up to, I think, 12 million acre-feet that we lost over that period of time.

Water Deeply: What happened as a result of that groundwater depletion?

Patton: Beginning in the 1990s, we had folks who had reduced spring flows filing what we call conjunctive administration water delivery calls. It’s a water-right action. If you have a water right that’s senior to folks who are pumping the same water through groundwater wells, and you are not getting your full supply, you have a right to go to the state and say, “State, shut off those junior guys who are pumping my water.”

Idaho has an extremely strong water rights administration process. Idaho has also gone down the conjunctive administration route, where we administer groundwater and surface water rights together in this real-time system.

There had been a lot of these conjunctive administrative delivery calls filed. Some threatened to shut down significant portions of the groundwater-irrigated lands on the Snake River Plain, in addition to water rights for cities and factories and other things. It was a big deal.

In 2015 the courts basically said, “OK, Department of Water Resources, you’ve been protecting the junior water rights holders a little too much at the expense of the seniors. You need to fix that.” That brought the parties to the negotiating table.

We arrived at a settlement in May 2015. It required the groundwater users to reduce their pumping by about 240,000 acre-feet a year. The parties also supported a state recharge agreement of 250,000 acre-feet a year. One of those is designed to stop the ongoing drop in the aquifer, and the other will rebuild the aquifer.

Water Deeply: How have the recharge efforts gone so far?

Patton: That first winter, 2014–2015, we were able to recharge 75,000 acre-feet into the aquifer. It wasn’t our full target, but it was a good start. The following year was about the same, even a little less, but it was a drier year. Then the winter of 2016–2017 we were able to hit 317,000 acre-feet of recharge. We exceeded the goal.

In some years, we’re not going to have 250,000 acre-feet available to recharge. So we know in those wet years we’ve got to exceed the target to make up for the dry years.

It’s really more a goal of keeping the system in balance rather than putting a certain amount in. We want to first stop the drop in the aquifer. Then we want to rebuild it to a certain amount that was spelled out in the settlement.

Water Deeply: Where does the money come from for the recharge program?

Patton: A couple of different sources. Some of it is state general fund monies. And then some of it comes from the state cigarette tax. We get up to $5 million a year from the cigarette tax, though sometimes it’s variable, so $5 million is our cap. And then we get $5 million a year from the general fund.

Water Deeply: Was there any objection to using those funding sources?

Patton: No. This region of the state we’re talking about accounts for a major share of Idaho’s economic output. So anything that puts that at risks gets attention really quickly. And Idaho is an agricultural state, and it always will be, at least in my lifetime. There is very strong support for managing our water resources and maintaining our water systems in the state.

Water Deeply: What are the main expenses for the program?

Patton: The money goes for building facilities and operating the program. We enter into contracts with irrigation districts or canal companies that divert from the Snake River. So we’re using their facilities, usually during winter, when they’re not running their own water in them. A chunk of that money goes to pay them to do that.

Water Deeply: What facilities is the state building for groundwater recharge?

Patton: Because we’re running water through those canals built for irrigation use, some of it is retrofitting those canals to be able to carry water when it’s icing up, to protect things in the canal from ice damage.

We’re also building big spreading basins at various locations along these canals. That means acquiring land, in some cases renting land, and in some cases getting easements from the Bureau of Land Management or state lands.

We’re still planning to build a lot more capacity. Right now we probably have enough built to put 300,000–400,000 acre-feet in the ground during a big flood year. What we really need is the ability to recharge 600,000 acre-feet a year, so we can average 250,000 acre-feet year in and year out.