Work on aquifer near local airport, will provide data that will shed light on its sustainability

For several years, City of Prineville public works staff has been trying to learn as much as possible about an aquifer beneath the local airport.

In 2006, they drilled a well near the facility that yielded a much better water supply than any drilled on the valley floor. The result inspired them to drill another well nearby, which essentially came up dry.

Since then, the city has tried to figure exactly where they will hit water and how much they can draw from the source before outpacing the rate the aquifer regenerates. The effort has included help from a variety of people, and recently, they gained new data from a Portland State University student that will help them further map the water source.

While working with Ken Lite, a hydrologist with the Oregon Water Resources Department, City Engineer Eric Klann was presented with a proposal.

“He (Lite) is an adjunct professor at Portland State,” Klann recalls. “He called me up and said he had this young lady (Erin Dunbar) who is going to get her master’s degree needs a master’s project. What do you think about having her study the aquifer?”

Klann was willing to oblige and the city committed $20,000 to fund the research, a fraction of the cost the city would have paid if they contracted the work elsewhere.

“With that, she went in and took the cuttings of all these different (test) wells,” he said. “Whenever we drill a well, every 10 feet we take a sample. She took that study even further than we had. What she did is X-ray fluorescents where they scan these rocks to try to determine where all the layers of the material came from.”

Dunbar spent about a year and a half on the project, and recently presented her findings to the Prineville City Council.

“My objectives were to look at the geology in the area and create a stratigraphic sequence of what’s going on underground,” she explained. “My job was to go through the samples and determine what they were.”

Dunbar examined 616 different samples and organized them in rock chip trays that showed what test well they came from and from what depth. She noted that much of the area contained sediments from lava flows as far away as the Cascades, and remnants from the Crooked River.

She determined that in general, 130 to 200 feet below the surface is comprised primarily of basalt rock from lava flows. Beneath that, 200 to 400 underground, are river deposits that consist of gravel, sand, and mud. Below that lies more lava flow deposits.

The research will accompany the work carried out by the city during the past three years. They first completed a study where they looked at existing wells to map the aquifer, determining that it is an ancient riverbed. From there, they dug three test wells.

“What we were trying to do there was find the bullseye of the target and the edges of the target,” Klann said.

Since drilling those wells two years ago, they have been trying to understand the sustainability of the water source in order to determine how much they can pump from it.

“She took the data to a new level,” Klann said of Dunbar’s work. “We have a better understanding of the geology, and now we need to roll that back in (to the rest of the research).”

The city hopes to finish the aquifer study within the next year and a half, at which time they will use the information to develop a new water master plan. While Klann acknowledged that Dunbar’s work didn’t prompt any “ah ha” type moments, he believes it will help them develop a more accurate picture of the needed water source.

“Whenever you have a complex question like this, the more information you have, the better decisions you can make,” he said.

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