The Central Valley is home to California’s productive farming belt, but the region’s groundwater is so severely overdrafted in some places that the land has been sinking. Problems with subsidence started decades ago, but have been made worse by California’s drought, which is now in its fifth year.

Now scientists from Stanford University have found that the region might actually have three times more groundwater than previous estimates, which are decades old.

But this newly discovered water comes with caveats – it’s deep down, at depths of 1,000–3,000ft (300–900m), which means it could be more saline; and drilling that far down will not only be much more expensive, it could lead to further land subsidence that could damage buildings and infrastructure. And much of these hitherto unknown water sources happen to be close to oil and gas wells, which puts them at risk of being contaminated.

The study, published in the journal Proceedings of the National Academy of Sciences today, highlights the need to better characterize and protect deep groundwater aquifers, not only in California but also in other parched regions such as Texas, China and Australia.

“The question is not whether there is water, but whether there’s sufficiently good-quality water that we could use for drinking water or other uses,” said Mary Kang, study coauthor, an environmental engineer and researcher at Stanford.

While it’s good news that we do have more water than we thought we had, “we need to be prudent about how we use it,” cautioned Robert Jackson, study coauthor, who is a professor and earth scientist at Stanford.

Oil and Water Do Not Mix

But could we actually drill that far down into the earth?

Back in the day, no one considered drilling more than a couple of hundred feet down because it was too expensive to go further down, but now with prolonged droughts, water at 1,000ft is widely used, Jackson pointed out.

California and most of the western states are distinct in having deep fresh groundwater, but in California, oil and gas activity often happens close to some of these aquifers.

This was especially apparent in Kern County, where Bakersfield and the surrounding areas are a hub of oil and gas activity, including hydraulic fracturing or fracking, which involves injecting fluids into the earth to crack rock formations that hold oil and gas. Wastewater is also sometimes discharged by injection back into the earth, including into deep aquifers.

“Kern County had the most freshwater and the highest percentage of oil and gas activity in the freshwater,” Jackson said. “The concern is that there is little monitoring. The state may want to consider other permits for example, for oil and gas activity that occurs nears fresh groundwater.”

It was a similar scenario in Fresno County, but farther north in Colusa County there were very few energy explorations near freshwater sources.

Study Based on Extrapolation of Data

Jackson and Kang were interested in finding out how much water California had underground, so they used state databases to analyze deeper water chemistry. Their results are based on an extrapolation of previous estimates and data from the California Department of Conservation, Division of Oil, Gas and Geothermal Resources, referred to as the DOGGR database, which has data sheets on oil and gas fields and wells. The database includes not just fracking, but also injection wells and other activity.

Some of the data goes back to 1920, although they only used data going as far back as the 1960s and 1970s. They tapped data from 938 oil and gas pools and more than 35,000 oil and gas wells to characterize both shallow and deep groundwater sources, and analyzed eight counties in the region where they had enough data to build a model of how much groundwater there might be deep down.

“The groundwater is not just limited to the Central Valley. I looked at areas with quite a bit of oil and gas development, but if you look in Los Angeles and San Diego, it might be there,” Kang said.

Jackson explained that we have very little data on aquifers at more than 250ft (76m), because many states and countries have not thought too much about groundwater, but oil and gas wells provide data at much deeper levels.

Identify and Protect Deep Fresh Groundwater

An onion farm is irrigated in Arvin, Calif. An aquifer deep under the Central Valley was newly identified by researchers from Stanford but it’s too soon to know if it would provide water for the agricultural region in the near future. (Ric Francis, AP)

Given this is smack dab in the middle of the farming belt, should growers be salivating at this newly discovered water?

“For someone looking deep underground for water, it presents an opportunity and some risk,” Jackson said. “Nothing we found changes the observation that we have been pumping groundwater at rates that are completely unsustainable. We’re not advocating the use of this new groundwater, but just identifying it.”

While most of the extra water they found was between 1,000 and 3,000ft, their study actually went much further – to depths of 9,000ft (2,750m).

“We looked at whether we’re safeguarding this water today. We looked at risk analysis of what pumping might do. And what additional safeguards for shallow oil and gas activities might be warranted,” Jackson said.

The researchers said this was a first order estimate, and more sampling is needed to refine their estimate, before studying what would happen if we were to pump this far down for water.

“We need more data, current data, not just old data,” Kang said. “This kind of work should also be done in other places, because it’s worth characterizing deep ground water resources, which should be monitored and protected.”