The Pennsylvania Environmental Hearing Board (EHB) has granted Sunoco Pipeline LP’s request to resume horizontal directional drilling (HDD) for the Mariner East (ME) 2 pipeline at select sites across the state to preserve equipment and prevent environmental damage.

The EHB had already granted the company’s motion to rotate downhole drill bits and reamers at dozens of sites to safeguard equipment, but allowed the company to finish HDD operations at 16 sites in nine counties along the pipeline’s proposed path, where Sunoco argued it couldn’t stop without causing harm to the project or the environment.

The EHB ordered HDD to stop at 55 sites across the state on July 25 after the Clean Air Council, Mountain Watershed Association and the Delaware Riverkeeper Network released documents detailing more than 61 spills that had been reported by Sunoco during construction activities. The groups also filed an application asking for a temporary suspension of HDD operations as part of their broader appeal of the project’s permits. A hearing that was scheduled for Monday to extend that suspension while the broader case is decided has been postponed until Wednesday and is expected to last through the end of the week.

Sunoco requested approval to resume HDD at the sites to avoid the collapse of drilled holes, which it said can create safety issues, damage equipment and cause environmental harm. The company argued, among other things, that the bentonite in its drilling mud could settle out of its water mixture and increase the risk of more fluid releases and spills. The locations where HDD has resumed, Sunoco said, share common subsurface characteristics.

Other construction on the project continues, including open-trench operations and conventional road boring. The company has not started HDD at another 168 locations.

The environmental groups filed their appeal in February after the state issued permits for the project and construction began. The groups argue that the pipeline would cause irreparable environmental harm. They got more firepower for their cause last month when more than a dozen families in the southeast part of the state reported losing water pressure and murky water where HDD for the project was underway.

Drilling mud — a mix of nontoxic bentonite clay and water — affected groundwater and private water wells in the area, leading Sunoco to pay for municipal water connections at the affected homes. The state Department of Environmental Protection also fined the company $87,600 for wetland violations and issued four other violations for fluid releases.

The 350-mile pipeline would transport ethane, butane and propane from Ohio, Pennsylvania and West Virginia to the Marcus Hook Industrial Complex near Philadelphia for domestic and international distribution. Sunoco still expects the project to be completed in two phases this year and next.