Is the oil industry fracking up California’s drinking water?

California officials ordered an emergency shutdown last month of 11 oil and gas waste-injection sites—and a review of more than 100 others—in the state’s drought-wracked Central Valley out of fear that companies may have been pumping fracking fluids and other toxic waste into drinking-water aquifers there.

On July 7, the state’s Division of Oil, Gas and Geothermal Resources issued cease-and-desist orders to seven energy companies, warning that they may be injecting waste into aquifers that could be a source of drinking water and posing “a danger to life, health, property, and natural resources.” State officials say the investigation is expanding to look at additional wells.

The action comes as California’s agriculture industry copes with a drought crisis that has emptied reservoirs and cost the state $2.2 billion this year alone. The lack of water has forced farmers across the state to supplement their water supply from underground aquifers, according to a study released last week by UC Davis.

The problem is that at least 100 of the state’s aquifers were presumed to be useless for drinking and farming because the water was either of poor quality or too deep underground to easily access. Years ago, the state exempted these aquifers from environmental protection and allowed the oil and gas industry to intentionally pollute them. But not all aquifers are exempted, and the system amounts to a patchwork of protected and unprotected water resources deep underground. Now, according to the cease-and-desist orders issued by the state, it appears that at least seven injection wells are likely pumping waste into freshwater aquifers protected by the law, and not into other aquifers sacrificed by the state long ago.

A 2012 ProPublica investigation of more than 700,000 injection wells across the country found that wells were often poorly regulated and experienced high rates of failure—outcomes that were likely polluting underground water supplies that are supposed to be protected by federal law. That investigation also disclosed a little-known program overseen by the U.S. Environmental Protection Agency that exempted more than 1,000 other drinking-water aquifers—many of them in California—from any sort of pollution protection at all.

Those are the aquifers at issue today. According to documents the state filed with the U.S. EPA in 1981 and that were obtained by ProPublica, the exempted aquifers were poorly defined and ambiguously outlined. They were often identified by hand-drawn lines on a map, making it difficult to know today exactly which bodies of water were supposed to be protected. Those exemptions and documents were signed by Gov. Jerry Brown in 1981.

State officials emphasized that they will now order water testing and monitoring at the injection well sites in question. “We do not have any direct evidence any drinking water has been affected,” wrote Steve Bohlen, the state oil and gas supervisor, in a statement.

Bohlen said his office was acting “out of an abundance of caution.” A spokesperson said the state became aware of the problems through a review of facilities it was conducting according to California’s fracking law passed late last year, which required the state to study fracking impacts and adopt regulations to address its risks, including underground disposal.

California officials have long been under fire for their injection-well practices, a waste-disposal program that the state runs according to federal law and under a sort of license—called “primacy”—given to it by the EPA.

For one, experts say that aquifers the states and the EPA once thought would never be needed may soon become important sources of water. Indeed, towns in Wyoming and Texas—two states also suffering long-term droughts—are pumping, treating and delivering drinking water to taps from aquifers that would be considered unusable under California state regulations.

In June 2011, the EPA conducted a review of other aspects of California’s injection-well program and found enforcement, testing and oversight problems so significant that the agency demanded California improve its regulations and warned that the state’s authority could be revoked.

The EPA’s report also said that California regulators routinely failed to adequately examine the geology around an injection well to ensure that fluids pumped into it would not leak underground and contaminate drinking-water aquifers. The report found that state inspectors often allowed injection at pressures that exceeded the capabilities of the wells and thus risked cracking the surrounding rock and spreading contaminants. Several accidents in recent years in California involved injected waste or injected steam leaking back out of abandoned wells, or blowing out of the ground and creating sinkholes.

The exemptions and other failings, said Damon Nagami, a senior attorney with the Natural Resources Defense Council in an email, are “especially disturbing” in a state that has been keenly aware of severe water constraints for more than a century.

“Our drinking water sources must be protected and preserved for the precious resources they are, not sacrificed as a garbage dump for the oil and gas industry.”