Two natural gas midstream operators in western Pennsylvania have agreed to improve their facilities after the U.S. Environmental Protection Agency (EPA) said they failed to comply with Clean Air Act (CAA) rules to prevent accidental releases of flammable substances.

Under one settlement, MarkWest Liberty Midstream & Resources agreed to install appropriately sized emergency vents on its condensate storage tanks and adopt an approved maintenance schedule at all 14 of its compressor stations in Pennsylvania’s Washington and Butler counties.

The MarkWest compressor stations receive natural gas from well sites, then separate out the liquids from the natural gas and route the liquids to aboveground storage tanks at the facilities.

In a separate settlement, the owner and operator of the Laurel Mountain Midstream Robin Hill facility in Washington County agreed to conduct a safety analysis and make necessary improvements. The natural gas processing plant is owned by Laurel Mountain Midstream Operating and operated by Williams Field Services Co. The companies also agreed to coordinate and conduct training with local emergency responders.

EPA conducted inspections at 10 of the 14 MarkWest facilities and the Robin Hill facility in late 2011 to determine compliance with CAA Section 112(r), prevention of accidental releases to air. As a part of the settlement, the companies did not admit or deny EPA’s allegations.