Sonoma County drills wells to study groundwater sustainability

The shallow wells Sonoma County’s water agency is drilling near 11 waterways have nothing to do with delivering water to 600,000 residents of Sonoma and Marin counties.

Instead, the 21 wells will serve as measuring sticks to determine whether pumping groundwater in the county’s three basins - the Santa Rosa Plain, Petaluma Valley and Sonoma Valley - is curbing the flow in creeks inhabited by federally protected fish and other species.

The $300,000 project is the latest consequence of a state law, enacted during California’s five-year drought, requiring long-term sustainability of underground water supplies that were heavily tapped during the prolonged dry spell.

And that means assessing the connection between surface water and groundwater and possibly, for the first time in state history, setting limits on use of well water by residents, ranchers, businesses and public water systems.

“We can’t see what’s beneath the surface, so these monitoring wells will act like underground telescopes. They can help us see how much and when water is available,” county Supervisor Susan Gorin said in a statement.

Gorin is chairwoman of the Sonoma Valley Groundwater Sustainability Agency, which covers the basin seen as most susceptible to depletion. Local agencies were formed in 2017 in each of the county’s basins to implement mandates of the Sustainable Groundwater Management Act that became law in 2015 amid the state’s historic drought.

Farming interests generally have taken a dim view of the increased monitoring and prospect of pumping limits. During the recent drought, when stream flows were greatly diminished statewide, Central Valley farmers especially drew heavily on groundwater at rates that officials said were unsustainable, risking a whole host of related environmental impacts - on drinking water, soil and wildlife.

Still, regulation of groundwater use is a new thing in California, and local grape growers have eyed it warily, concerned about new restrictions on their businesses.

“Nothing good for farmers in this county … can come from this monitoring,” Jim Bundschu, an owner of Gundlach Bundschu Winery in Sonoma, told the Board of Supervisors in 2016, when representatives of the county’s wine industry lobbied for a greater say in the new regulations. “Agriculture needs a larger voice.”

The government agencies overseeing each of the three local basins have the ability to register and monitor wells, restrict pumping and prevent drilling of new wells. Agencies also have the ability to assess new fees and taxes.

This month, as part of the new monitoring initiative, a red drilling rig bored into the ground close to Paulin Creek, where it passes under a bridge at Hardies Lane north of West Steele Lane.

Twenty feet down, the drill hit water, no surprise to Mitch Buttress, a Sonoma Water hydrogeologist supervising the work.

“We’ve been seeing water at 20 to 30 feet,” he said, referring to the wells previously sunk, with nine more to go this month.

After months without rain, underground water tables are generally at their lowest level and will “climb back up” when storms return, Buttress said.

The new wells will only be about 50 feet deep, far shallower than water supply wells that go down hundreds of feet. An instrument to measure water level and temperature every hour will be tucked inside a 2.5-inch PVC pipe. In the adjacent creeks, a gauge will measure the water flow, providing side-by-side reports on surface and subsurface water.

The data, which will be made public, will inform deliberations by the local groundwater agencies to set thresholds for well water pumping to avoid “unreasonable depletion” of stream flows, said Marcus Trotta, a principal hydrogeologist with Sonoma Water.

It will also help determine where creeks may serve the important function of recharging aquifers and indicate where the agencies may want to consider future groundwater recharge projects, Trotta said.

Underground aquifers and surface water in creeks and rivers have a complex relationship, with the aquifers in some cases feeding creeks and at other times drawing water from them.

When the drilling is done, there will be five wells on both Mark West Creek and Sonoma Creek, two each on the Laguna de Santa Rosa and Santa Rosa Creek and one each on Colgan and Paulin creeks, as well as Adobe, East Washington, Capri and Lichau creeks in Petaluma and the Petaluma River.

The state Department of Water Resources is paying for the wells at a cost of about $15,000 per well. The state agency has also provided $3 million to cover the operating costs of the three groundwater agencies.

The well project funding “is a big boon to our community and the information provided will be invaluable,” said Supervisor David Rabbitt, the board chairman who also heads the Petaluma Valley basin agency.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.