Readers were surprised to learn from my Sunday story that oil companies are allowed to send their drilling muds and boring waste into unlined pits.
They do it with a waiver that was granted several years ago. The Central Valley Regional Water Quality Control Board does not view the muds and waste as a hazardous discharge.
But the waiver will expire next month. Environmental groups are pressing the state to end the waiver and require more protection for the underground water table.
My Sunday story was not about the muds or boring wastes. It was about a separate and controversial practice of hydraulic fracturing, or fracking, which includes the use of chemicals to help free up oil trapped in shale formations.
Fracking fluids were illegally discharged into two of those unlined pits, called sumps. Regional water authorities found the chemicals in concentrations above safe thresholds.
The regional board is now investigating the sumps of several dozen oil companies in the San Joaquin Valley.
The concern is that the contamination might wind up in drinking water systems and irrigation water.
The contaminated sumps are both near Shafter in Kern County, which produces most of the oil in the Valley and in the state. The sumps and wells are owned by Vintage Production, a subsidiary of Occidental Petroleum Corp.
To be abundantly clear: The drilling muds and boring waste are not part of fracking, which takes place after the well is drilled. The muds and boring waste have long been considered a low threat.
The Center for Biological Diversity says the muds and wastes themselves contain many kinds of chemicals to help reduce friction and make the drilling more efficient. Some chemicals are related to gas and diesel.
The group, representing many activists, says the time has come to regulate it.