Agency finds Petaluma groundwater clean, cheap

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As Petaluma’s new groundwater regulatory agency turns one, there is good news for residents living in the Petaluma groundwater basin. Preliminary tests show the basin is relatively healthy, and residents likely won’t be asked to contribute funding for the new government body in the near future.

The Petaluma Groundwater Sustainability Agency was formed last June in response to state legislation that required a local management plan for all of California’s groundwater basins. It is a result of the recent multi-year drought that saw the groundwater table in several parts of the state sink to dangerously low levels.

The agency’s main task is to survey the Petaluma groundwater basin — a 46,000-acre area that includes the city of Petaluma and surrounding agricultural land — and identify a plan to combat potential problems including a drop in water level or poor water quality.

“The basin is in good shape,” said Ann DuBay, the administrator of the GSA. “That is great. Now, how do we make sure it stays in good shape in the future?”

The United States Geological Survey has provided preliminary data, which the agency will ultimately use to make its sustainability plan. Rural residents outside city limits rely on groundwater from around 1,000 wells in the basin. Residents in Petaluma largely get their water from the Sonoma County Water Agency’s Russian River aqueduct, but the city maintains several groundwater wells for emergency supply.

The study shows that groundwater levels in the basin are relatively stable, except in the northwest Petaluma Valley, where levels are in decline. Historical data show nitrate infiltration into the groundwater in the western ranch lands, but the recent survey shows the problem is decreasing.

Historical data also showed saltwater intrusion into the groundwater basin through the tidally influenced Petaluma River, but that stopped around 1962. The latest USGS study will look at whether changing land uses has caused saltwater to increase in the basin.

The USGS study results should be finalized this year, and the groundwater agency will use that to formulate its sustainability plan by 2022, DuBay said. Some strategies include expanding urban water conservation practices to the rural areas to encourage farmers to use water more efficiently.

“Everyone in the basin will be affected in some way,” DuBay said. “The real focus is on those outside the city.”

The agency’s $470,000 annual budget comes from contributions from the city of Petaluma, Sonoma County, the water agency, North Bay Water District and Sonoma Resource Conservation District. At some point, officials acknowledge that the agency will need to find its own funding source.

The board will vote in August on a funding plan for the agency, but members are leaning toward holding off on a tax or fee until after the sustainability plan is finalized in four years.

“What would we be charging for?” said Supervisor David Rabbitt, the chair of the groundwater board. “We need to produce a plan first.”

A rate and fee study produced several options that officials could adopt for charging residents for the agency. Options include a flat fee or tax charged to the landowner of each parcel in the basin, a fee or tax charged to landowners for each acre of land they own, a fee or tax charged to landowners based on the type of land they own and the way they use their land, and a fee or tax charged to a well owner for each gallon of water pumped from the aquifer.

Rabbitt said that all stakeholders, including city residents, should bare some of the cost for creating a sustainable groundwater basin.

“If everyone pays a little, we’re all better off,” he said.

(Contact Matt Brown at matt.brown@arguscourier.com.)

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