It is National Groundwater Awareness Week, and the state of California is aware. It knows every aspect of its groundwater. How does that knowledge help Bay Area counties replenish their underground basins?

Every 12 days, a radar satellite passes 430 miles above the state, mapping the sinking surface with centimeter-scale accuracy. From 2020 to 2023, a helicopter zigzagged across priority aquifers towing a 100-foot hoop that sent electromagnetic signals into the ground to model its geological architecture in depths of down to 1,000 feet.

Every day, 386 global positioning stations record the movement of groundwater basins. And 8,500 groundwater monitoring wells collect and send reports on water levels and water quality.

All of this data is funneled to the California Department of Water Resources, where it is combined to produce three-dimensional models that describe, down to grain size, the ever-changing properties of the state’s groundwater aquifers. It is publicly available on the California Natural Resources Agency Open Data portal at

This happened as part of the Sustainable Groundwater Management Act, or SGMA, which is marking its 10-year anniversary this year.

The urgency to paint this detailed picture spiked in the aftermath of a mega drought from 2012 to 2016, the driest period in the state’s recorded history. As reservoirs shrank, Californians turned to drawing water from the state’s 515 groundwater basins, adding to historic and irreversible subsidence and reducing their capacity to store water.

“That historic drought was actually the impetus for the passage of the Sustainable Groundwater Management Act,” said E. Joaquin Esquivel, chair of the State Water Resources Control Board, in a Monday webinar.

Low water drought conditions at Folsom Dam and Lake located in Sacramento and El Dorado counties. Photo taken January 26, 2014. (John Chacon/California Department of Water Resources via Pagransen)

About 83 percent of Californians rely on groundwater for some portion of their water supply, according to DWR director Karla Nemeth. Water supply needs met by groundwater can shift between 40 to 60 percent depending on the kind of water year. Some communities depend on groundwater for 100 percent of their supply.

“Even when we have wet conditions, we still have 40 percent of California that is reliant on those groundwater supplies,” Nemeth said.

Ten years ago, SGMA established a network of local groundwater sustainability agencies, or GSAs, to oversee and improve their own subbasins. By 2017, over 250 agencies had formed, managing over 130 basins, representing 98 percent of all groundwater pumped in California.

“This is about being stewards for the entire basin, not just for the members of their irrigation agencies, but all the groundwater uses, including groundwater dependent ecosystems,” said Paul Gosselin, deputy director of sustainable groundwater management for DWR.

Out of the 515 groundwater basins, the state identified 94 as being high and medium priority, 21 of which were deemed critically overdrafted. All agencies had to submit a plan by 2020 to reduce groundwater usage by 2040. Today, 71 of those plans have been officially approved by the DWR, including agencies representing large swaths of the Central Valley. Thirteen are incomplete and six are deemed inadequate.

This is about being stewards for the entire basin, not just for the members of their irrigation agencies, but all the groundwater uses, including groundwater dependent ecosystems.

Paul Gosselin, deputy director of sustainable groundwater management for DWR

According to analysis by DWR, Gosselin said, half a million acres of farmland will need to be brought out of production by 2040, particularly in the San Joaquin Valley. Some farmers may also elect to skip a year and offer their fields to be used as recharge sites if their soils are right for the job.

The SGMA provided agencies with the funds to drill monitoring wells and fill data gaps and shared that data with the public. It provided the newest information on planning for climate change; guidance on how to recharge groundwater supplies; how to work with neighboring basin managers; how to engage with communities in multiple languages; how to participate in water markets and how to use farmland as recharge basins.

GSAs must submit different types of progress reports every spring and fall, every year and every five years.

“Since 2016, we have awarded over half a billion dollars for SGMA planning implementation,” said Gosselin in the webinar Monday.

The Eastern San Joaquin groundwater basin was determined to be critically overdrafted, according to Alex Chetley, deputy director of development at San Joaquin County Public Works. The GSA for that basin got money to add about 5 or 10 new monitoring wells to fill the data gaps between their existing 250 wells.

The basin needs to reduce groundwater pumping by about 90,000 acre feet over 20 years to achieve this goal, he said. Their approved plan includes sending surface water back down the same pipes used to pump groundwater up. Users would still pump from wells, but if the wells are replenished, they would end up using less total groundwater.

“So, the idea is wet year storage for dry year use,” said Chetley. 

Mitigating seawater intrusion

In Monterey County, the Salinas Valley basin in the Castroville area first experienced seawater intrusion back in the 1930s.

“A lot of the wells were going to salt water in the coastal Castroville area,” said Shaunna Murray of the Monterey County Water Resources Agency.

In 1998, local agencies produced a recycled water project. They designed a system to irrigate a 12,000-acre area with a blend of treated wastewater, well water, and river water.

“So, it is somewhat nimble with the different drought climates and different issues that it can take,” she said.

The GSA for the Castroville Seawater Intrusion Project has received over $3 million in SGMA funds for monitoring and improvements. 

With climate change and rising sea levels bringing a future risk of saltwater intrusion, water agencies can benefit from creative examples like the one in Castroville.

“The options for the farmers are pretty dire,” Murray said. “Most of their wells have gone to sea water so they don’t have another option.”