Napa Valley groundwater pumping exceeds sustainable yield

Groundwater pumping in 2021-22 was 18,790 acre-feet, according to a new report. It was the third consecutive year that pumping exceeded the Napa Valley sub-basin’s sustainable yield of 15,000 acre-feet, coinciding with a three-year drought.

Taking a longer view, the seven-year annual pumping amount of 18,023 acre-feet also tops the sustainable yield.

This doesn’t mean the Napa Valley sub-basin will be sucked dry anytime soon. But experts say even this year's rain bonanza won't be a cure-all and that changes are needed. The county is aiming to reduce groundwater usage.

“We want to maintain a balance and address these uncertain weather extremes,” consultant Vicki Kretsinger Grabert said. “So conservation is essentially becoming a way of life in Napa County. It doesn’t matter what kind of water year type it is, drought or deluge.”

The Napa County Groundwater Sustainability Agency on Tuesday heard the annual groundwater report for the water year running from October 2021 to September 2022.

Well water in Napa Valley comes from the 72-square-mile Napa Valley sub-basin. The sub-basin is a kind of underground reservoir where permeable sediments soak up and hold water — and, like surface reservoirs, the supply drops if more water is used than is replenished.

Groundwater beneath the valley floor is pumped mostly for agriculture, as well as for businesses and homes. Those supplies are crucial to the success of wine country and the local economy. Groundwater also feeds the Napa River and creeks during hot summer months, helping fish and aquatic life.

Napa County uses a system of monitoring wells to keep track of what’s going on beneath the ground.

The 2021-22 year brought some red flags, which the groundwater report calls “undesirable results.” One is a reduction in groundwater storage. The other is a depletion of water in surface waterways that can be fed by groundwater.

Grabert talked about climate change and the more extreme weather patterns of recent years.

Napa County Supervisor Ryan Gregory — the Board of Supervisors members sit as the Groundwater Sustainability Agency board — said this rainy season’s big storms should help replenish the sub-basin. But he also heeded Grabert’s message.

“What you’re saying is, don’t get comfortable, because the (rainy) years we're having are far and few between,” Gregory said.

Napa County is aiming for a 10% reduction of overall groundwater pumping from the average seen between 2005 and 2014. Grabert talked about a voluntary water conservation push among groundwater users, with mandatory restrictions if that doesn’t work.

Supervisors Joelle Gallagher and Anne Cottrell noted some groundwater users already do much to conserve, while others don’t. They wanted to take this into account.

A coming step is completing work plans for pumping reductions, water conservation, interconnected surface water and stormwater resources. Then the county will look at implementing the plans.

Even as supervisors spoke, another atmospheric river storm pounded the area, the latest in a series to sweep California since late December. The rainfall could be seen through the windows of the Board of Supervisors chamber in downtown Napa.

“Hopefully, it buys us time so we can keep doing the work we need to do,” Cottrell said.