Construction on the $2.5-billion Mariner East 2 pipeline in Pennsylvania has resumed following a month-long state investigation into numerous environmental permit violations that resulted in a $12.6-million civil penalty against Sunoco Pipeline LLP. The Pennsylvania Dept. of Environmental Protection suspended the project permits on Jan. 3, citing the contractor’s use of unapproved construction techniques, fluid leaks into waterways and groundwater contamination. The agency said in a statement that Sunoco has taken steps to ensure that remaining construction activities will be conducted “in accordance with the law and permit conditions” and that the firm will be allowed to resume work, albeit under closer monitoring. Construction controversies and citizen lawsuits have beset the 350-mile pipeline project, which will carry natural gas liquids across Pennsylvania from the Marcellus Shale areas to a refinery south of Philadelphia. With the project already 18 months behind schedule, Sunoco reportedly has switched from tunneling to open-trench construction in several locations to better safeguard water resources. Officials of Delaware County, where the refinery is located, recently declined to conduct a risk assessment of the project’s potential impacts to nearby neighborhoods.