Three environmental groups sued Wednesday to block construction of Sunoco Pipeline LP's Mariner East 2 pipeline, which state regulators allowed to resume on Feb. 8 after Sunoco agreed to pay a $12.6 million fine for permit violations.

Sunoco, which has fended off such suits in the past,  is building the pipeline system to carry Marcellus Shale natural gas liquids like propane across state to its export terminal in Marcus Hook. Construction has been plagued by complications including leaks of clay-like drilling fluids, some of which have fouled private water wells.