A regional water board voted Thursday to end a paperwork and fee waiver that for 30 years allowed oil companies to dispose of well drilling fluids in unlined sumps at will.

The 4-1 vote by the Central Valley Regional Water Quality Control Board means drillers now will have to apply for permission to dump, file detailed disclosure forms and pay a fee of nearly $2,000 per well or cluster of wells.

Also known as drilling mud, the fluids are intended to cool or lubricate drill bits. Although recipes vary, they tend to be salty with high concentrations of dissolved solids.

The board's concern is that drilling fluids can increase the salinity of groundwater, which limits its value for irrigation and drinking.

Thursday's vote in Sacramento was welcomed by the Center for Biological Diversity, an Arizona-based environmental group that had pushed for an end to the exemption, saying an earlier review on dumping drilling fluid in unlined sumps was inadequate.

"Oversight of these toxic drilling muds is long overdue," CBD attorney Hollin Kretzmann wrote in a news release.

The oil industry had tried to persuade the agency the fluids posed no harm.

Rock Zierman, president and CEO of the California Independent Petroleum Association trade group, said the end of the drilling fluid exemption would burden oil companies and agency staff alike.

The sump disposal exemption expired Wednesday. The board acted to extend it for other kinds of businesses -- including Kern County growers -- just not well drillers.

Clay Rodgers, assistant executive officer in Fresno for the water board, said staff will conduct an analysis to see how much of a threat drilling fluid presents, and then determine what is the best method for disposing of it.

The question of whether to renew the oil exemption gained notice earlier this year when Vintage Production California LLC, a local oil producer that's part of Los Angeles-based Occidental Petroleum Corp., was found to have dumped hydraulic fracturing fluid -- which was not covered by the exemption -- in an unlined sump for 12 days last fall. The water board fined $60,000 for the incident.