Feds document shrinking San Joaquin Valley aquifer

California's San Joaquin Valley has lost 60 million acre-feet of groundwater since 1961, according to a new federal study. That's enough water for 60 Folsom reservoirs.

This is among the findings in a massive study of groundwater in California's Central Valley by the U.S. Geological Survey. It helps shed light on the mysteries and dangers of California's groundwater consumption, which is mostly unregulated.

According to the study, groundwater pumping continues to cause the valley floor to sink, a problem known as subsidence. This threatens the stability of surface structures such as the California Aqueduct, which delivers drinking water to more than 20 million people.

The Central Valley is America's largest farming region; it's also the single-largest zone of groundwater pumping. About 20 percent of groundwater pumped in America comes from under the Central Valley, said Claudia Faunt, the study's project chief.

In the Sacramento Valley, the study found groundwater levels have remained stable. Virtually all of the groundwater loss has occurred in the San Joaquin Valley, where aquifer levels have dropped nearly 400 feet since 1961, she said.

The current drought has aggravated this problem.

"In most years, especially in the San Joaquin Valley, the groundwater pumping exceeds the recharge," said Faunt, a USGS hydrologist. "With recent times, those groundwater levels have dropped back down close to historical lows."

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