Two gas companies violated federal clean air rules in Washington County and reached settlement agreements with the U.S. Environmental Protection Agency, it announced Tuesday. MarkWest Energy Partners LP had several storage tanks that continually released vapors, didn't have emergency vents and didn't get regularly scheduled maintenance, according to the consent order. Laurel Mountain Midstream Operating, a pipeline company operated by Oklahoma-based Williams Cos. Inc., owns a processing plant in Robinson where it did not fully implement its risk management plan and had no fire protection system, among other issues. Both companies agreed to fix the problems but did not admit to any violations. The agency will decide on fines or other enforcement steps after the companies finish the corrections, spokeswoman Bonnie Smith said.