Horizontal directional drilling (HDD) operations for Sunoco Pipeline LP’s Mariner East (ME) 2 project may resume across Pennsylvania after the company reached a settlement with environmental groups and agreed to a series of additional safeguards.

The agreement with the Clean Air Council, Mountain Watershed Association and Delaware Riverkeeper Network was reached Tuesday. The order finalizing the settlement was filed Wednesday with the Environmental Hearing Board (EHB), more than two weeks after the EHB ordered the company to stop HDD operations at 55 sites. The settlement does not affect the environmental groups’ broader appeal of the project’s state permits.

HDD was allowed to resume at select sites last week to protect the environment and equipment, but the settlement lifts the full suspension. It’s unclear when Sunoco may resume work at sites where construction has stopped or how the new requirements may affect the project’s in-service date. The company said the agreement would allow it to proceed with HDD but provided no details. It also said it is prepared to comply with the enhanced standards for planning, outreach and reporting.

Sunoco must re-evaluate most of the sites, including examining the geology and conducting a re-route analysis, among other things. The company is also required to submit a report certified by a professional geologist to the state Department of Environmental Protection (DEP) and the environmental groups. The DEP would then have 21 days to review the submissions and decide if further action or permit modifications are necessary.

Other construction activities have continued since February, when state regulators issued water-crossing and sedimentation permits. The company had not started HDD at 168 locations when the EHB ordered drilling to stop last month.

More than a dozen families in the southeastern part of the state reported water problems early last month in an area where HDD was underway for ME 2. The state has since fined Sunoco and issued violations for a series of drilling fluid spills. As part of the settlement, Sunoco must notify landowners within 450 feet of HDD operations 10 days before they begin or restart. Landowners would also be able to have their water tested before HDD begins.

The 350-mile pipeline is designed to transport natural gas liquids from Ohio, Pennsylvania and West Virginia to the Marcus Hook Industrial Complex near Philadelphia for domestic and international distribution. It now is scheduled to come online in phases beginning later this year.