State officials allowed oil and gas companies to pump nearly three billion gallons of waste water into underground aquifers that could have been used for drinking water or irrigation. Those aquifers are supposed to be off-limits to that kind of activity, protected by the EPA. California's Department of Conservation's Chief Deputy Director, Jason Marshall, told NBC Bay Area, There have been past issues where permits were issued to operators that they shouldn't be injecting into those zones." In "fracking" or hydraulic fracturing operations, oil and gas companies use massive amounts of water to force the release of underground fossil fuels. The practice produces large amounts of waste water that must then be disposed of. Marshall said that often times, oil and gas companies simply re-inject that waste water back deep underground where the oil extraction took place. But other times, Marshall said, the waste water is re-injected into aquifers closer to the surface. In the State's letter to the EPA, officials admit that in at least nine waste water injection wells, the waste water was injected into "non-exempt" or clean aquifers. For the EPA, "non-exempt" aquifers are underground bodies of water that are "containing high quality water" that can be used by humans to drink, water animals or irrigate crops. "It should not have been permitted," said Marshall.