Sunoco Pipeline LP said it resumed horizontal drilling of its Mariner East 2 underground pipeline near Exton on Saturday after temporarily suspending operations last week when a dozen Chester County families complained the drilling impaired their private water wells.

The Newtown Square company said that families whose water became cloudy or interrupted were receiving bottled water or additional filtration. "We're staying in close touch with neighbors to monitor for any continuing issues," said Jeff Shields, a Sunoco spokesman.

Sunoco put as many as five families up in local hotels for several nights after the incident, which was first reported to authorities Monday.

The company is conducting horizontal directional drilling under Township Line Road in West Whiteland and Uwchlan Townships, where it is installing the second of three pipelines. Through them, Sunoco is delivering natural gas liquids, such as propane, from the Western Pennsylvania shale fields to its terminal in Marcus Hook.

Although most of the pipeline's 350-mile route is being built near the surface in a trench, Sunoco is using horizontal directional drilling methods to install the pipeline through much of densely populated areas of Chester and Delaware Counties. The technique involves drilling a bore through bedrock, sometimes quite deep, through which the coated steel pipe is inserted.

Nontoxic bentonite clay is used as a lubricant to cool the drill bit and to transport bits of excavated rock back through the borehole to the surface. Officials suspect the bentonite seeped into groundwater supplies, causing the water wells to become cloudy.

Shields said that measures were taken to stabilize the drill hole and to prevent infiltration of the aquifer.

Sunoco, the Pennsylvania Department of Environmental Protection, and Aqua Pennsylvania said that public water wells near the pipeline route were unaffected.

Sunoco has promoted the $2.5 billion project as a critical link from the Marcellus and Utica Shale fields to the Delaware River port, where most of the petroleum products will be exported to European petrochemical plants, though some of the propane is also sold into local markets. The project has sparked protests and lawsuits from adjoining landowners and environmentalists.