Aquifer gets MRI

As Butte County and other agencies head toward a distant but firm deadline to finalize plans for managing groundwater, many questions remain unanswered. The most significant may be the most basic.

What’s down there?

Scientists such as Christina Buck, assistant director of the county’s Water and Resource Conservation Department, and Todd Greene, an associate professor of geology and environmental science at Chico State, have been studying the local aquifer system for years. They know what’s in specific spots—sites of wells and bore holes—but have had to extrapolate expanses in between.

Until now. Thanks to a 21st century upgrade of World War II technology, with a boost from—of all places—Denmark, both Butte and Glenn counties will have a better understanding of the underground layers where water flows and caches. This knowledge, apart from the scientific benefit, will inform groundwater sustainability plans required by 2022 under the state’s Sustainable Groundwater Management Act (SGMA).

“We may picture things differently than we have in the past,” Buck told the CN&R. “We will have visualizations of our aquifer system that we’ve never had before—and I think that will potentially affect how we choose to talk about some portions of our aquifer system and how we portray them.”

SGMA, she explained, requires management plans to include a “hydrogeologic conceptual model,” which essentially comprises “a narrative of how your groundwater system works … and responds to changing conditions.” This survey will magnify that model.

Buck gave her explanation at Haigh Field in Orland, in view of the helicopter and equipment that will make this breakthrough possible. Adding locally allocated funds to monies from California and Danish governments, Butte County is participating in one of three pilot studies in the state. Experts, including specially trained geologists, analyze aerial scans of groundwater basins to ascertain the composition and structure.

Basically, our aquifer is getting an MRI.

“That’s pretty correct,” said Jim Cannia, senior geologist with Aqua Geo Frameworks, the Nebraska-based firm conducting the study. Much like magnetic resonance imaging in health care, the airborne electromagnetic (AEM) technology sends down signals that bounce back to a receiver. Data-processing software helps Cannia and his associates interpret the responses, filter man-made objects such as power lines and create a 3-D image.

The data come from an octagonal ring that hangs 100 feet below a helicopter whose pilot keeps the apparatus 100 feet above the surface for optimal scanning, to 1,200-foot depths, and consistent surveying. The ring directs electromagnetic waves into the earth, Cannia said; “then the rocks get energized and they send off a secondary signal.” A receiver at the rear of the ring captures the secondary signal.

This occurs every 25 feet along the flight line. The Butte route covers almost 500 miles, crossing into Glenn County to gauge areas where two aquifer systems meet.

“So what you end up with,” Cannia added, “by the time we end up flying this, is thousands and thousands of virtual bore holes that tell us what the geology is here.”

Danes play a part in this project because of their pioneering role in AEM. The system used here, SkyTem, was developed in Denmark, which implemented its own version of SGMA 20 years ago. Cannia’s firm sends raw data to Danish experts for preliminary processing.

“They’re very proud of this technology,” said Lisa Hunter, Glenn County’s water resources coordinator, who traveled in October to tour AEM and water facilities there. “They’ve used this technique across Denmark, and they’d like to be known for some of their groundwater management techniques and data management systems.

“Theirs is a small country; when people think of them, LEGOs come to mind, or Hans Christian Andersen, or The Little Mermaid. They’d also like groundwater management to be up at the top of the list.”

Ergo, support for this project.

Cannia explained that the root of AEM goes back to World War II, when it was utilized to find submarines “because it loves metallic objects.” In the decades since, advances in computing have expanded applications and continually made the technology more powerful. Hydrologists (i.e., scientists who study water systems) have benefited particularly.

For its finalized survey, due to the county in April, AGF will cross-reference its findings with records from well logs and bore holes, compiled in a digital format by Greene at Chico State. This helps validate the AEM data, Cannia said: “None of this is done by itself.”

That groundwater map should answer the overarching question—What’s down there?—by resolving details.

Greene, science director for the university’s Center for Water and the Environment, wants to know how shallow and deep zones “communicate” basin-wide. “If you drill for this lower one and pump water out,” he said, “is the upper one going to be affected?” The way to determine is looking for a “seal,” or impermeable barrier, and any leaks.

“Usually when we have one well here and a mile away another well, we’re trying to guess in between” Greene added. “This [survey] fills in a lot of those gaps.”

Buck’s queries also include how the eastern side of the Tuscan Aquifer system transitions to the hard-rock lava cap, such as in the foothills by Butte Valley, to learn “what are the flow paths for the precipitation that seems to be recharging the shallow and the deep zones of the aquifer”; and, in Glenn County, what’s the geological geography “in the interfingering zone where Tuscan material from the east meets Tehama formation material from the west.”

The latter, she said, “could lead to better coordination between [SGMA plan areas] as well.”