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Overflights surveying North Bay groundwater basins this weekend and early next week

Tentative Schedule for Airborne Electromagnetic Surveys

Big Valley Basin (Kelseyville/Lake County) Saturday, Nov. 13

Ukiah Valley Basin (Mendocino County) Sunday, Nov. 14

Santa Rosa Valley/Santa Rosa Plain Monday, Nov. 15

Petaluma Valley Tuesday, Nov .16

Napa-Sonoma Valley/Sonoma Valley Wednesday, Nov. 17

Source: Department of Water Resources

If you think you see a very large, very strange object flying overhead in the coming days, it’s not your imagination.

The state Department of Water Resources is launching a specially equipped helicopter over the region this weekend that will be flying low and dangling a 100-foot-wide hoop that will send electromagnetic signals into the earth. The signals will bounce back and be recorded on onboard instruments.

The flights are part of a three-year effort to collect data on the geological structures and characteristics of key groundwater basins around California to enhance sustainability planning and focus future groundwater recharge efforts.

After working in more northerly parts of California earlier this week, the helicopter is expected to fly over the Big Valley Basin the Kelseyville area of Lake County on Saturday, followed Sunday by the Ukiah Valley Basin in Mendocino County.

The survey crew is tentatively scheduled to arrive Monday in Sonoma County, where it will fly the Santa Rosa Plain, the Petaluma Valley and the Napa-Sonoma Valley over the following two to three days.

Each basin has been identified as a medium- or high-priority groundwater basin under the state 2014 Sustainable Groundwater Management Act.

Though the time required to synthesize and interpret data from the Airborne Electromagnetic Survey program means it won’t be available to help with the first round of local groundwater basin plans due to the state in January, AES data will be of value as five-year updates are drafted in the future.

The data and hydrologic mapping that results also should aid development of engineering projects like flood management, water conveyance and infrastructure.

Diagrams based on subsurface geophysical data collected through airborne electromagnetic surveys describing groundwater aquifers, potential recharge areas and pathways. (Department of Water Resources)
Diagrams based on subsurface geophysical data collected through airborne electromagnetic surveys describing groundwater aquifers, potential recharge areas and pathways. (Department of Water Resources)

“We’re excited to have the state come in and help us,” said Jay Jasperse, chief engineer and director of groundwater management at Sonoma Water, “because this is going to help us improve our plans.”

The survey technology was developed in Denmark and has been tested in California as part of a pilot project, though it’s also been used nationally and internationally, according to Katherine Dlubac, engineering geologist for the Department of Water Resources and AES project manager.

She said it’s completely safe, generating about the same electromagnetic field exposure as a common toaster or standing mixer. “It’s really very minimal,” Dlubac said.

It’s carrying an awkward load, however — a large, hoop frame about 100 feet in diameter suspended 100 feet below the aircraft, she said — so the flight path is generally outside densely populated areas.

The larger reason, however, is that highly urbanized areas produce too much electromagnetic noise that interferes with data collections. Metallic structures, pipelines, rail lines and other infrastructure render the exercise moot.

Dlubac said electromagnetic signals emitted by the airborne instruments gather information about electrically conductive and resistive materials underground. That is used to help define where there are course grain materials, like sand and gravel, that might allow water to filter through, as well as fine grained silts and clays that would inhibit water flow.

Diagrams based on subsurface geophysical data collected through airborne electromagnetic surveys describing groundwater aquifers, potential recharge areas and pathways. (Department of Water Resources)
Diagrams based on subsurface geophysical data collected through airborne electromagnetic surveys describing groundwater aquifers, potential recharge areas and pathways. (Department of Water Resources)

Electromagnetic surveys also can help map fault lines, Jasperse said, and “can also help you kind of, in the broad sense, understand about saline groundwater instruction — where there’s brackish water — which is especially important in Sonoma Valley and Petaluma Valley, because of San Pablo Bay.”

“There’s a lot of good information that can come from this technology,” he said.

Dlubac said aircraft flies in a grid pattern to assess the spatial reach and depth of different subsurface properties, filling in gaps in data largely dependent on decades of observations made by well drillers, as well as more recent hydrologic modeling.

“Now we have more continuous data that provides us more of a three-dimensional understanding of these layers,” Dlubac said.

The $12 million project is funded through Proposition 68, a $4 billion general obligation bond approved by voters in 2018 for drought, water, parks, climate, coastal protection and outdoor access programs.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.

Tentative Schedule for Airborne Electromagnetic Surveys

Big Valley Basin (Kelseyville/Lake County) Saturday, Nov. 13

Ukiah Valley Basin (Mendocino County) Sunday, Nov. 14

Santa Rosa Valley/Santa Rosa Plain Monday, Nov. 15

Petaluma Valley Tuesday, Nov .16

Napa-Sonoma Valley/Sonoma Valley Wednesday, Nov. 17

Source: Department of Water Resources

Mary Callahan

Environment and Climate Change, The Press Democrat

I am in awe of the breathtaking nature here in Sonoma County and am so grateful to live in this spectacular region we call home. I am amazed, too, by the expertise in our community and by the commitment to protecting the land, its waterways, its wildlife and its residents. My goal is to improve understanding of the issues, to find hope and to help all of us navigate the future of our environment. 

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