In the midst of the worst drought in California’s history comes news that hydrofracking operations are polluting the state’s dwindling water supplies.

In July, during the height of the drought, state regulators halted operations at 11 injection wells used to dispose of wastewater used in hydraulic fracturing. The state found that the wastewater might have contaminated aquifers used for drinking water and farm irrigation. The Environmental Protection agency had ordered the state to send them a report regarding the situation within 60 days.

Last week, in compliance with the EPA demand, the California State Water Resources Board sent the agency a letter confirming that at least nine of the sites closed down by the state were indeed dumping contaminated water into aquifers protected by the Safe Drinking Water Act and California regulations.

A copy of the letter was obtained by the Center for Biological Diversity. The letter reveals that some three billion gallons of toxic wastewater was illegally released when injected into wells and spread into aquifers in the central part of the state. The State Water Resources board also stated that water samples taken from eight water supply resources close to the injection sites have excessive levels of toxins and carcinogens, including thallium, a chemical found in rat poison, and arsenic, a known carcinogen which can also wreak havoc on the endocrine and immune systems of humans and animals.

“Arsenic and thallium are extremely dangerous chemicals,” said Timothy Krantz, a professor of environmental studies at the University of Redlands. “The fact that high concentrations are showing up in multiple water wells close to wastewater injection sites raises major concerns about the health and safety of nearby residents.”

State regulators believe that up to 19 other fracking wastewater injection wells could have contaminated aquifers. To date, the Water Resources Board has only tested the eight wells indicated in its letter.

Anti-fracking and water activists are calling on Gov. Jerry Brown to put a moratorium on fracking, especially considering the state’s severe water shortage. They point out that fracking poses a great threat to the health and safety of California’s residents in several ways.

First, fracking is very water intensive, and the water used cannot be treated for later use by people, industry or agriculture. The water-intensive process takes up to 150,000 gallons out of the regional water cycles each time a well is fracked. Second, there is the concern about the contamination of water resources. Also, both the fracking process and the amounts of oil and gas that will be consumed as a result will create great amounts of atmospheric carbon, further contributing to climate change and possibly creating or exacerbating droughts in the future.

The drought in California is on the verge of becoming a crisis as dozens of communities in the state are reporting they’re on the verge of running out of water. Some say they will have no water in as little as 60 days.

Many of the communities at the crisis point are small and isolated, according to Tim Quinn, of the Association of California Water Agencies. Such communities often rely on one water source, without backups, to provide for their customers. Quinn warns, however, that even more sophisticated water districts may find themselves in trouble next year.

Currently, 14 communities are on the “critical list,” meaning they’ve informed the state that they’ve reached a point where they don’t believe they will have adequate public water within the next two months. Some of these communities have turned to trucking in water for now while they look for long-term solutions to the drought’s impact on their water systems. California’s 154 reservoirs are about 50% below their historical average.

The U.S. Drought Monitor, a government-funded weekly map of drought conditions, reports that 82% of the state is experiencing a severe to exceptional drought, with 58% suffering from the harshest of drought conditions. The entire state has been suffering from drought conditions since May, the first time in 15 years.

In July, California imposed statewide water-use regulations on residents for the first time. State regulators approved stringent measures limiting outdoor water, including a $500 fine for using an outdoor hose without a shut-off nozzle.