"Oil Wastewater Dumped Into Shallow Central Valley Wells"

"California officials have identified 260 oil company wastewater injection wells that are so shallow or so close to wells used for drinking or irrigation that they could threaten the state’s precious groundwater supplies, new data show.

All of the wells inject water left over from oil field operations into aquifers that were supposed to be protected by law. While most of those aquifers contain salty water that would need treatment before use, state and federal officials want them preserved as a potential supply for cities and farms in the future.

So far, no wells used for drinking or irrigation have been found to be tainted by the injections. But in a letter to the U.S. Environmental Protection Agency on Friday, the California office that oversees oil drilling said it would seek water-sampling data from each of the wells. The office — the Division of Oil, Gas and Geothermal Resources — has ordered 23 wells shut down so far."

David R. Baker reports for the San Francisco Chronicle May 18, 2015.