Napa County’s second annual groundwater checkup shows largely stable water levels in 2015 following the fourth year of California’s drought, but sounds a few notes of caution.
Last year, the county saw for the most part stable groundwater conditions, with a little dip of water levels in some areas, consultant Vicki Kretsinger Grabert told the Board of Supervisors.
“There’s some response to the drier conditions, but overall, things are generally looking pretty good,” Grabert said.
In contrast, San Joaquin Valley groundwater levels are plummeting. Drought-battered farms have chased water by drilling wells as much as 2,000 feet deep and over-drafted aquifers are causing the ground in some areas to sink several inches annually.
Napa County has escaped that fate, though it has its own set of problems.
Groundwater can be found along the Napa Valley floor at depths of 10 feet or less in some places, Grabert told supervisors on April 5. Water levels can be deeper along the valley edges where soils are less permeable.
As usual, the water-depleted Milliken-Sarco-Tulocay area east of the city of Napa – the Coombsville area—remains a concern. The 2015 report found the water level decline in some wells has moderated since 2008, while it is still falling in others.
Supervisor Keith Caldwell wants to see what will happen to Coombsville water levels with a new, $14 million recycled water project. Pipes this spring will bring recycled water from the Napa Sanitation District sewage treatment plant to the Coombsville area for irrigation, which should lead to less pumping.
In addition, the county wants to further study an area northeast of the city of Napa near Petra Drive and Silverado Trail that has seen groundwater declines. Several winery projects are proposed there.
Groundwater levels in this northeast area may or may not be related to the Coombsville conditions, Grabert said. The effect on the Napa River is unknown, she said.
Supervisors expressed interest in studying the northeast area at a cost of $89,000. Among other things, a study could help the county determine whether groundwater extraction rules similar to those in the Coombsville area are warranted.
Napa County’s water world is far from simple.
“The geology is complex, not only on the mountainsides, where it’s very complex, but even on the valley floor,” Grabert said.
She talked about Napa County “groundwater budgets.” That takes into account such factors as rainfall and runoff from the hills and water percolating into the ground and people pumping water from wells.
“That is like a bank account — what do we have going into our bank account, what do we have going out and what do we have in reserve?” Grabert said.
The watershed water budget along the Napa River near Napa is an annual average of 70,600 acre-feet of recharge and 21,300 acre-feet of pumping, she said. One acre-foot of water is about 326,000 gallons.
Chris Malan, who is running for the 4th District supervisor seat in the June 7 election, told supervisors she’d like a public discussion on such issues as salt water intrusion, fish kills and streams going dry. She’s talked to six people on Atlas Peak in recent months who have had trouble with wells.
In general, the results of the 2015 groundwater report were similar to the results reported in the 2014 report. Monitoring well sites ranged from Napa Valley to the Carneros region to Angwin to the Lake Berryessa area.
The county looked at 113 well monitoring sites, most on the Napa Valley floor. These wells help gauge the health of the underground reservoirs that serve Napa County’s world-famous vineyards and wineries and its rural homes and businesses.
“Everyone living and working in Napa County has a stake in protecting the county’s groundwater resources, including groundwater supplies, quality and associated watersheds,” the report said.