Chevron Corp. said that tests of the recycled oil field wastewater it sells to farmers in Kern County meets water quality standards, and does not contain contaminants an advocacy group claimed it found.

After treating it, Chevron provides 21 million gallons of the wastewater per day to the Cawelo Water District, which distributes it to 90 farms in the area for agricultural irrigation.

An advocacy group called Water Defense reported that it had tested the water in 2014 and early this year and detected methylene chloride and acetone in the samples.

Chevron said the testing methods used Water Defense were flawed. It said its own recent tests of the water found no traces of the chemicals, and that the water it provides to the district meets the agency’s standards. Chevron said earlier tests it performed did detect small amounts of acetone and benzene, but these were likely the result of natural biological processes.

“We know of no operational source of acetone within Chevron’s oil field processes in the San Joaquin Valley,” said Cam Van Ast, a spokesperson for the San Ramon-based oil company.