A 10-year study by the U.S. Geological Survey (USGS) confirmed what environmentalists and other sentient beings have been saying for decades: California is messing up its groundwater.

One-fifth of the 11,000 wells tested turned up high levels of man-made and naturally occurring contaminants that are especially troublesome when not treated at relatively small venues. The researchers said they studied data from 99% of the state’s public water systems.

Big water systems take steps to bring their water up to state and federal standards, but California has 250,000 private wells where the homeowner takes care of water quality. Around 8.9% of Californians rely on groundwater to drink, but nine out of 10 public water systems use it to some extent.

High concentrations of naturally-occurring contaminants, like arsenic and uranium, were found in 20% of wells. And high doses of human-made contaminants, like nitrates and solvents, appeared in around 5%. Unfortunately, the human stuff shows up in groundwater relied upon by large groups of people, like in the San Fernando, San Gabriel and Santa Ana basins of Southern California.

High concentrations of nitrates, generally associated with fertilizer in agricultural areas, were found in groundwater beneath urban areas that were converted from agricultural use decades ago. Livermore Valley and parts of the Santa Ana Basin were noted.

The study also found agricultural areas, like the San Joaquin and Sacramento Valley, which did not have high levels of nitrate at depths tapped for drinking, but warned that could change soon.

Californians have been tapping groundwater at a furious pace as surface sources of water dry up in the drought. It’s hard to say exactly how much water is being pumped out where because the state doesn’t make its water logs public, unlike every other Western state. Water agencies have won the same level of confidentiality about their pumping activities that the law accords residential and commercial users.

The state is only now beginning to find out what’s in the wastewater oil and gas drillers let sit around in pits or inject back into ground in the vicinity of—and into—aquifers. And at some point they hope to add “how much” and “where” to “what.”

The study is included in California’s Groundwater Ambient Monitoring & Assessment Program (GAMA) being implemented by the State Water Resources Control Board. It was published in the Environmental Science & Technology journal of the American Chemical Society

–Ken Broder

To Learn More:

Study Finds Contaminants in California Public-Water Supplies (by Ellen Knickmeyer and Scott Smith, Associated Press)

Decade-Long Study Shows Natural Contaminants More Prevalent than Human-Made Contaminants in California Groundwater (U.S. Geological Survey)

California Finally Gathers Groundwater Data, but Won’t Reveal It (by Ken Broder, AllGov California)

Metrics for Assessing the Quality of Groundwater Used for Public Supply, CA, USA: Equivalent-Population and Area (by Kenneth Belitz, Miranda S. Fram and Tyler D. Johnson, U.S. Geological Survey)