The project area included a total of eight collapsed mine portals with at least five of them having discharges ranging from 1 to 10 gpm. Total flows were estimated to be between 25 and 30 gpm. Thrasher’s scope and plans for this project included construction of an access road into the site, excavation and wet seal of at least eight deep mine portals and the re‐grade and fill of subsidence sinkholes. To carry water safely off site, drainage control channels, conveyance pipe and under drain were constructed.
This project involved the elimination of subsidence depressions, the closure of open portals and the treatment of AMD. The Roaring Creek Wa‐ tershed was heavily deep mined and surfaced mined prior to 1977. The project area consisted of 3 open and 3 closed portals discharging AMD. The AMD seeped along the unnamed tributary and an area of subsidence, which drained surface water into the mine workings. AMD flow from the deep mine portals ranged from 10 gpm to 100 gpm with PH ranging from 3.1 to 5.0. The seeps along the UNT showed an average PH of 3.3. Thrasher’s design plans called for the construction and rehabilitation of access roads to the site, and installation of wet seals at the portal locations.