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Groundwater management plan underway


Plan must be adopted by end of year to stop or reverse local groundwater declines

By Jay Gamel

If everyone drawing water from wells from Glen Ellen to San Pablo Bay can’t voluntarily stop or reverse declining water levels throughout the groundwater basin, mandatory measures may be put into place. The Sonoma Valley Groundwater Basin is tapped by residential, agricultural and commercial users every day for over half the total water use for the whole valley.

The Sonoma Valley Groundwater Sustainability Agency (SVGSA) is currently developing a long-range plan that must be submitted to State Water Resources directors, who are looking at a second round of rate and fee studies that may be put into place. SVGSA hosted a virtual meeting on June 23 to describe the progress on a formal plan and take public input.

Questions asked by the 45 public participants centered mainly on use of graywater, possible fees on residential wells, and plans for increasing groundwater storage capacity. Participants were also surveyed about their concerns with groundwater management. More than 80 percent had their own wells, and half used their water for home use. While most lived in the southern part of the basin, people living throughout the basin attended.

Forty-two percent have seen their well levels decline in the past 10 years, with 13 percent reporting having a well go dry.

The meeting focused on describing the groundwater basin, setting goals for the sustainability plan, looking at possible actions to achieve those goals, and setting up a continuous monitoring plan.

A formal Groundwater Sustainability Plan must be adopted by the end of the year. It is supposed to resolve groundwater declines within 20 years from adoption. Contemplated measures include asking for more voluntary conservation and more water use efficiency actions as a first step. Percolating stormwater into the ground can be done at farms and vineyards, where possible users can pump water back into the ground, and finally there could be mandatory conservation and efficiency measures, according to Marcus Trotta, principal hydrogeologist for the Sonoma County Water Agency (Sonoma Water).

Groundwater declines in the Sonoma Valley Water Basin were officially recognized by a 2006 geological survey underwritten by Sonoma Water and performed by the U.S. Geological Survey.

Sonoma County has the largest number of residential wells in the state, so it’s no accident that the first three groundwater basins targeted for possible future regulation — unheard of in the wild west — are in this county.

What you may not know, is that Sonoma Valley’s groundwater basin is the most impacted of the three, which include the Santa Rosa Plain and the Petaluma Basin. It has an estimated 1,500 wells, including domestic, mutual water company, agricultural, and public water supplies (like Kenwood Village Water and the Valley of the Moon Water District).

Physically, the basin features extensive fractured geology, with both a shallow (under 200 feet) and a deep aquifer (200+ feet), making collecting accurate data expensive, but not impossible, Trotta said. The two aquifers are generally separated by a layer of clay, sometimes rock.

Over 50 percent of the basin relies on groundwater, with 35 percent using imported water from the Russian River, 10 percent recycled water, and just 3 percent using surface water.

The new groundwater law, The Sustainable Groundwater Management Act (SGMA – called ‘Sigma’), “fills in a piece of the water puzzle that most people didn’t know was missing, and they won’t notice the new law either,” Caitlin Cornwall said. Cornwall is vice-chair of the Advisory Committee, as well as a Sonoma County Planning Commissioner.

“The ones who are most likely to be affected are big groundwater users on the valley floor, like vineyards, Sonoma Valley’s water retailers, maybe the golf course, maybe some cannabis growers,” she said.

Key issues are figuring out how to measure and monitor groundwater loss and how to know when mandatory measures may be needed, Finding a “quantitative, measurable objective,” isn’t easy, Cornwall said, adding that milestone indicators have to be put into play to know if the plan is working and to initiate additional actions.

“Using science, models, and data can provide most of what we need to know,” Cornwall said. One of the most difficult elements is the long range involved in measuring, with cycles coming in multiple years. A single year’s drastic decline or increase in groundwater is not a trigger point for action.

Groundwater levels, subsidence, seawater intrusion, depletion of surface water, and degraded water quality will be the main criteria monitored.

Deciding the “significant and unreasonable” minimum thresholds for each of these criteria will have to be determined to trigger mandatory action. That is likely to be an ongoing process.

To date, there has been no ground subsidence in the basin and the water quality remains good.

While noting that groundwater is vital not only to residents, but to the county’s premier income sector, the wine industry, Cornwall noted that animals and ecosystems are also beneficial users of groundwater and are vital to the long-term viability of the forests and wildlands that use most of the water that goes into the ground.

Statistics indicate that from 2012 through 2018, agricultural pumping shows a mean of 3,400 acre feet a year, with all the rest accounting for 1,900 acre feet. An acre foot of water represents one foot of water covering one acre.

In the south county, toward San Pablo Bay, groundwater levels are already 100 feet below sea level, and saltwater in some form has intruded as far as El Verano.

SGMA of 2014 requires California counties to develop long-term plans to halt and possibly reverse groundwater depletion by 2040. Sigma called for formation of new groundwater sustainability agencies (GSAs) to develop plans for specified groundwater basins, and submit them for approval to the State Water Resources Board by early 2022.

A public review of the draft Groundwater Sustainability Plan will be available this fall. More information may be found at