A local oil producer may face closer scrutiny and the industry in general more regulation after water quality watchdogs found a second instance of unauthorized chemical dumping in a Shafter-area pond.

The Central Valley Regional Water Quality Control Board has determined that Vintage Production California LLC, part of Los Angeles-based oil giant Occidental Petroleum Corp., discharged oilfield fluids into two sumps near Shafter.

An agency official said Wednesday that the state may now want to test other sumps owned by the company.

The findings add momentum to a staff proposal to tighten scrutiny of the local oil industry's waste disposal practices. Trade groups have said such a move would increase oil producers' costs by requiring more paperwork.

In the Central Valley, oil companies are only allowed to dump drilling fluid and mud into unlined sumps. Such materials are intended to remove cuttings and cool or lubricate drill bits; they are not considered a threat to groundwater.

As long as all they're dumping is drilling fluid, oil field operators do not need to fill out hazardous waste discharge reports.

But that may change if agency staff proceed with a recommendation, expected later this year, to end a 30-year-old paperwork waiver on drilling mud discharges.

"We're questioning the assumption that it's always going to be drilling mud," said Douglas Patteson, a supervising water resource control engineer at the agency.

A spokeswoman for Vintage declined Wednesday to comment on the agency's findings other than to say that addressing the issues raised by the water board "is a top priority" for the company.

Under state law, Vintage faces fines of up to $5,000 per day for unauthorized discharges, which according to a July 23 water board report took place Sept. 30 and Oct. 6 through Oct. 8.

Those dates refer to previously reported instances of dumping at a Shafter-area Vintage well. The activity was evident in an online video showing workers discharging fluids into an unlined sump. The video was filmed by local farmer and environmentalist Tom Frantz.

The agency has since determined that between 89 and 175 barrels (3,738 to 7,350 gallons) of unauthorized oil fluids were discharged into the sump.

The fluids -- none of which were permitted for discharge into the sump -- consisted of potassium chloride water, liquids that naturally exist in oil formations, and "linear fluid."

An agency investigator wrote that linear fluid is similar or identical to mixtures used in the controversial but highly effective technique known as hydraulic fracturing. "Fracking," as it is also known, pumps water, sand and small concentrations of sometimes toxic chemicals underground at high pressure to release oil and gas.

Water board staff learned of the unauthorized dumping after Vintage had already closed the sump. Unable to test its fluids, they found a similar sump the company operated nearby.

At the second sump they found chloride and boron at levels exceeding allowable limits. They also found benzene and petroleum hydrocarbons with gasoline and diesel characteristics, all in concentrations at least 30 times higher than allowed in drinking water.

Two oil industry trade groups did not respond to requests for comment on the water board's findings and what they may mean to the future of the waiver program.

Frantz, who shot the video of dumping at the first sump, wrote in an email that the paperwork waiver "should never have been granted."

"These violations show we need greater protection from unscrupulous oil companies who greedily choose to take advantage of lax oversight," he wrote.