(RT) - Industry illegally injected about 3 billion gallons of fracking wastewater into central California drinking-water and farm-irrigation aquifers, the state found after the US Environmental Protection Agency ordered a review of possible contamination.

According to documents obtained by the Center for Biological Diversity, the California State Water Resources Board found that at least nine of the 11 hydraulic fracturing, or fracking, wastewater injection sites that were shut down in July upon suspicion of contamination were in fact riddled with toxic fluids used to unleash energy reserves deep underground. The aquifers, protected by state law and the federal Safe Water Drinking Act, supply quality water in a state currently suffering unprecedented drought.

The documents also show that the Central Valley Water Board found high levels of toxic chemicals - including arsenic, thallium, and nitrates - in water-supply wells near the wastewater-disposal sites.

Arsenic is a carcinogen that weakens the immune system, and thallium is a common component in rat poison.

“Arsenic and thallium are extremely dangerous chemicals,” said Timothy Krantz, a professor of environmental studies at the University of Redlands, according to the Center for Biological Diversity.

“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.”

The Center for Biological Diversity obtained a letter from the state Water Board to the US Environmental Protection Agency (EPA) that said the Central Valley Regional Water Board discovered the health violations. Following the July suspension of the 11 injection sites, the EPA ordered a review of aquifers in the area to be completed within 60 days.

The state Water Board also said that 19 more injection wells may have also contaminated sensitive, protected aquifers, while dozens more wells have been the source of wastewater dumped into aquifers of unknown quality.

Despite these damning findings, the extent of wastewater pollution is still undetermined, as the Central Valley Water Board has thus far only tested eight water wells of the more than 100 in the area, according to the documents. Half of those tested came up positive for containing an excessive amount of toxic chemicals.