A small city in the high desert of central Oregon takes advantage of an unusual geological feature to make its water supply more resilient.

Prineville, a city of 11,000 along the Crooked River, uses a confined aquifer deep underground that was an ancestral channel of the river. This channel was blocked by volcanic activity millions of years ago, but it still has characteristics of a riverbed, including rounded river rocks and gravel.

“It’s like a huge bathtub,” says Eric Klann, city engineer and public works director. “It’s not like a big cavern; it has gravels, and gravels leave a lot of areas that you can saturate. We can inject a huge amount of water.”

Prineville has drilled four wells into the confined aquifer; a camera sent down into the wells shows the interesting geological formation: “You are seeing lava, lava, lava and then all of a sudden you see these river rocks. You can actually see the water moving through those big river cobbles.”

Summer spikes

During spring, fall and winter, demand for water is well below the capacity of Prineville’s treatment plant. That means the city can treat more water than it needs and store the excess in the aquifer. In summer, when water demand is high, the stored water can be pumped out.

“The real beauty of aquifer storage and recovery is that the water treatment plant doesn’t have to be sized to meet my maximum demand,” Klann says. “We can run it a little bit harder than we need to in the winter and store a big amount of water, so that during the summer, when we need it, we can start pulling it out of the ground.”

The water plant has a capacity of about 3 mgd, Average demand in winter is about 1 mgd, but in summer, when residents are irrigating lawns and two large data centers need water for cooling, demand is 4 to 5 mgd.

“If we didn’t have the aquifer storage and recovery project, we would need a water treatment plant to meet the peak day demand,” Klann says. The city stored about 100 million gallons in the aquifer in 2021, and Klann anticipates storing as much as 800 million gallons to meet future demands. (Annual demand is about 650 million gallons.)

Similar projects

The aquifer storage and recovery project is not the first that Prineville has expanded its system without adding to its treatment facilities. In 2005, the city needed to expand its wastewater treatment capacity, and a consultant recommended building a $62 million mechanical plant.

Instead, the city built a 120-acre wetland to provide additional treatment at a cost of $7.7 million, part of it covered by grants. The wetland discharges to an aquifer that cools the water before it bubbles up into the Crooked River, benefitting the fish.

That project was one of five in the nation selected for a U.S. EPA Exceptional Project Pisces Award in 2018. It was also named Project of the Year in the 2018 Engineering Excellence Awards hosted by the American Council of Engineering Companies.

Prineville also boosted water system capacity without building with an aggressive leak detection and loss prevention program that started in 2007. It included replacing old wooden water mains, adding meters and meter-reading and billing software, and conducting regular audits. As a result, non-revenue water is down to about 2% from a high of 28%.

Data center support

Prineville is home to two large data centers, one for Apple and one for Facebook. Although they are the largest water users in the system and are large consumers in summer, their water demand is not very high on an annual basis.

“They like Prineville’s climate,” Klann says. “For the majority of the year, they use the outdoor air to cool their system. They can operate very efficiently here. When it’s really hot, they use a lot of water on a daily basis, but if you average it out, it’s not that high.”

The data center operators have supported Prineville’s efforts to expand the water system in cost-effective and environmentally sound ways. Apple provided the $8.7 million required to develop the aquifer storage system.

“We strive try to find environmental projects to meet their needs,” Klann says. “They really liked the wetland, and the aquifer project provides an environmentally sound source of water that is climate change resistant. That is a big deal.”

Help for the fish

The aquifer project has other environmental benefits. Prineville has several wells, some of them in shallow aquifers along the Crooked River. Those aquifers also support the flow of the river, home to steelhead, salmon and some endangered fish species.

When Prineville takes water from those shallow wells, it can mitigate any effects on the stream by releasing water from a reservoir about 20 miles upstream. The state Department of Fish and Wildlife determines when it is desirable to release the water.

The storage project also reduces the need to take water from the shallow aquifers in summer when stream flows are low and the river gets warmer. The treated water from the shallow aquifers is potable when it is stored in the deep aquifer, where it mixes with the water that is naturally there.

“The water in the aquifer does not have to be treated. It’s a much deeper aquifer,” Klann says. “With the shallow aquifer, we have issues with sulfur, manganese and iron. We’re just treating it for taste and odor issues. Once we resolve those issues, it’s similar to the water in that deeper confined aquifer. It happens to work out quite well.”