MarkWest Energy Partners LP continued to lead environmental remediation efforts in Wetzel County, WV, on Tuesday, three days after the company discovered that 3,000 gallons of chemicals had leaked from its Mobley Processing Facility.

West Virginia Department of Environmental Protection spokeswoman Kelley Gillenwater said the company called the state's spill line and the National Response Center on Saturday morning to report the release of heat transfer oil, identified as Dowtherm MX, from the Mobley facility in Smithfield, WV -- about 150 miles north of Charleston. While the company initially reported that all of the 10,000 gallons in its system had leaked, it later revised that estimate to 3,000 gallons.

Gillenwater said the chemical was released through a valve that failed and entered storm drains. The fluid was then released from the facility's storm water retention system and made its way into the tributary of a creek. Once the spill was discovered, she said, MarkWest staff closed off the stormwater outlet and stemmed the spill.

MarkWest spokesman Patrick Creighton added that samples taken Saturday indicated that heat transfer oil did reach the inlet of the nearby town of Pine Grove's fresh water treatment facility, but said it did not enter the public drinking water. Pine Grove has since been able to switch over to an alternate source of drinking water.

"While an investigation is underway on the cause of the release, MarkWest's singular focus has been on making sure our neighbors in Pine Grove have a source of clean water and the heat transfer oil is fully cleaned up from the [creek]," the company said in a statement on Saturday.

MarkWest said Tuesday that 11 additional water samples from nearby homes and businesses tested negative for the heat transfer oil, while three others from the affected creek showed reduced levels of the product as a result of the cleanup efforts. The company said Pine Grove residents can still have their water tested by calling a 24-hour response hotline.

Gillenwater said federal, state and local officials have responded to the cleanup efforts, which have involved vacuum trucks and booms. MarkWest said on Saturday that it had deployed more than 75 employees and contractors to help with the spill response, distribution of bottled water in Pine Grove and to help with the door-to-door notification of residents.

MarkWest plans to continue providing water to the town until sample results have determined that the water supply can resume inflow to the treatment plant and officials approve it for use.

MarkWest is now a subsidiary of Marathon Petroleum Corp.'s midstream master limited partnership MPLX LP (see Shale DailyDec. 1, 2015). The Mobley complex is a 520 MMcf/d cryogenic processing facility. The natural gas liquids recovered there are sent to the company's Houston plant for fractionation in Southwest Pennsylvania.