BELLEVUE - Rhonda Weakland carefully placed the seismometer on the dirt next to a field south of Bellevue.

A GPS unit joined it on the ground, with both plugged into a laptop. Then Weakland sat back to once again watch the data roll in for half an hour.

Both Weakland and James Bartolino, groundwater hydrologists with the U.S. Geological Survey, will do a lot of waiting over the next two weeks. The two are part of a team led by Bartolino, the district groundwater specialist, which is measuring the depth of the aquifer lying under the Wood River Valley.

Their portable seismometer is the same type used by scientists around the globe to track earthquakes, Bartolino said. Here, the device isn't used to seek out seismic events so much as document their absence, a technique new enough that the Blaine County work is a pilot project. By measuring the background vibrations - "white noise," as the scientists refer to it - and filtering them through a computer, the researchers can calculate the depth of the bedrock that marks the bottom of the aquifer.

That bedrock could lie anywhere from 30 to 1,000 feet deep in theory, Bartolino said, though he doesn't expect to find anything quite as deep as the latter. The study will likely incorporate measurements from about 100 points across the valley, including some side canyons.

"Nobody really knows how thick the aquifer is out here," he said.

Of course, the sensors pick up seismic events no matter what the scientists do. Cars driving past show up, and even trees swaying in the wind add to the noises bouncing around underground.

The scientists do their best to stay still and relatively quiet during each half-hour data session, minimizing their own contributions. Bartolino and Weakland carry two computers: while one collects data, the other can be used to analyze the last round, he said.

The data will eventually become the third of four reports planned on the Wood River Valley's aquifer system, building on past conclusions. For example, Bartolino said, he knows that water leaves the aquifer and the valley near Stanton Crossing. Measuring the depth of the aquifer there will help determine how much disappears.

The health of both the aquifer and the closely tied Big and Little Wood Rivers is important not only to the Wood River Valley, but also to water users downstream, stretching all the way to the Snake River. Bartolino said he still has remarkable support for his work. All nine funding partners - Blaine County, local cities and private groups - are still on board and even agreed to increase the funding for the current phase by 50 percent to $216,000, stretching it out over three years rather than two in the process.

Assuming everything goes to plan, Bartolino will start studying the region's water quality in the fall of 2011. He's already spent several years on the study, work he's enjoyed.

"It is fun being able to see something like this over the long term."