By Lois Henry, SJV Water
A groundwater agency on the western fringes of Kern County has taken the unprecedented step of banning all pumping from wells along the California Aqueduct for a 30-mile stretch.
The move is mainly designed to protect the vital artery that moves hundreds of millions of gallons of water a day from northern to southern California and is threatened by sinking land that could crimp its ability to function.
The ban is also intended to prove whether groundwater pumping is the true culprit.
“We don’t believe the subsidence is due to groundwater pumping,” said Mark Gilkey, general manager of the Westside District Water Authority. “But we don’t have the data to back that up. This was one of the ways we could prove groundwater pumping wasn’t the problem and safeguard the aqueduct, which is where we get all our water deliveries.”
He couldn’t say exactly how many existing agricultural wells would be impacted by the pumping ban as the authority also just started a mandatory well registration program to gather that data.
But because groundwater is so brackish in that area, the authority believes “…there is an extremely low density of consistently operational groundwater extraction wells,” Gilkey wrote in an email.
The authority also issued a moratorium on drilling new or replacement wells within the same “buffer zone,” which extends for 2.5 miles on either side of the aqueduct.
The drilling and pumping moratoriums don’t affect domestic wells nor oil and gas wells.

Tough decision
The Westside District authority is just one groundwater agency dealing with subsidence along a 164-mile stretch of the aqueduct through the San Joaquin Valley. The section that runs through Lost Hills has seen up to 4 feet of sinking. Other areas to the north have seen up to six feet.
But the Westside District authority is the only agency that has, so far, initiated a pumping ban to address subsidence, which has curbed the giant canal’s carrying capacity by 44% in some areas of the San Joaquin Valley.
“It was a tough decision,” Gilkey said. “But we felt it was the right thing to do.”
The groundwater authority is made up of the Belridge Water Storage District and Berrenda Mesa and Lost Hills water districts, which collectively, have contracts for 226,000 acre feet a year of State Water Project supplies.
Under the Sustainable Groundwater Management Act (SGMA), groundwater agencies must take action to prevent a host of “undesirable results” from overpumping, including subsidence.
“The actions by the Westside Authority are the boldest actions we’ve seen so far from any of the GSAs,” said Richard Yarborough, Deputy Director of the State Water Project, which operates the 444-mile long aqueduct bringing water from the Sacramento-San Joaquin Delta to Los Angeles. “We really applaud their efforts and see it as a sign they are taking concerns about impacts to key infrastructure seriously.”
In December, the Wheeler Ridge-Maricopa Water Storage District, south of Lost Hills, began its own well registration and extraction reporting program for wells in a 2.5-mile buffer zone along the aqueduct, according to General Manager Sheridan Nicholas.
As for pumping and drilling moratoriums, “Those are potential options included in our plans,” Nicholas said.
Other factors
The Westside District Authority moratoriums have also triggered a larger discussion about other factors that could be affecting the aqueduct, such as oil and gas extraction.
The Department of Water Resources and SGMA have no authority over oil production, Yarborough acknowledged.
“We’re trying to understand the process and what happens if subsidence isn’t being caused by groundwater extraction in this area,” he said. “So, we’re engaging with the Department of Conservation,” the agency that oversees oil and gas through the California Geologic Energy Management Division,CalGEM.
Yarborough recently sent CalGEM a comment letter urging a full environmental impact report for a proposal by Chevron to drill 75 new wells in the Lost Hills Oil Field because of its potential to exacerbate subsidence along the aqueduct.
That’s a significant reversal from findings in a 2019 Department of Water Resources report that blamed aqueduct subsidence on excessive groundwater pumping to irrigate nut trees and specifically exonerated oil and gas activities for sinking near Lost Hills.
“Several lines of evidence indicate that oil-field subsidence in the LHOF (Lost Hills and Northwest Lost Hills) does not extend east to the Aqueduct,” the 2019 report states.
DWR even sent letters to Kern County groundwater agencies at the time the report was released warning them against blaming oil and gas activities for subsidence and citing the report.
For its part, a Chevron spokesman said the company is aware of subsidence issues in the area and employs a management program under which it “…reinjects water at an approximate 1:1 ratio to the fluids extracted to manage localized subsidence in the field,” according to an email from the spokesman.
“We don’t know what’s causing the subsidence,” Gilkey said. “We have a lot of factors, including that the soils compact naturally in that area. We only have jurisdiction over groundwater pumping, so we’re trying to close that data gap.
Still, in its groundwater sustainability plan, the Westside District Water Authority includes several maps showing how thick clusters of oil wells directly overlay areas of subsidence.

A “serious problem”
Though subsidence has taken a significant toll on the aqueduct’s carrying capacity, water deliveries haven’t been shorted – yet.
“The aqueduct was built with a lot of extra capacity that lets us optimize operations,” Yarborough said. “But we’re getting to the point where we won’t be able to finesse it anymore and contractors will start to see impacts.”
One of those is the Metropolitan Water District of Southern California, which supplies water to a host of communities.
At the time the 2019 report came out, members of MWD’s Water Planning and Stewardship Committee wanted a lot more information and action from the state.
“We’ve got a serious problem,” said committee member Glen Peterson, of the Los Virgenes Municipal Water District during a meeting in 2020. “This affects more than half the state. The Legislature should take this up.”
So far, the state has put about $200 million into a pot for various aqueduct fixes, which Yarborough said are more along the lines of large maintenance projects, such as adding more concrete to increase the sides of the aqueduct and prevent overtopping in the sunken areas
There is no discussion, so far, of a wholesale rebuild, which was required on a section of the Friant-Kern Canal that had sunk due to excessive groundwater pumping.