APPLICATION OF WATER-LEVEL MONITORING TO TRACK OUTCOMES OF FLOODING BELOW-DRAINAGE MINES, 1980-2017: LESSONS LEARNED IN THE PITTSBURGH COAL BASIN

Near the end of the 20^th century, mines in the Pittsburgh coal of SW Pennsylvania/NW West Virginia underwent a regional process of closure and mine flooding. The federal Surface Mining Control and Reclamation Act (SMCRA) of 1977 for the first time regulated environmental effects of mine closures after that date, including mine water discharge. Operators of post-SMCRA mine closures needed to control and treat any future mine discharges for perpetuity or until mine-water quality became acceptable for discharge to streams. However, most mines abut other mines, separated by relatively thin barrier pillars, forming multiple complexes of mines that tended to flood together and required that control plans confront entire complexes. Mine operators were experienced in pumping and treating mine water and many had extensive databases of mine-water levels. This information became critical in the post-SMCRA years to monitor flooding progress and predict optimum locations for long-term pumping/treating of mine water. This study presents water-level case-histories from 3 areas of post-SMCRA closures that led to successful, though not always fully premeditated, control of mine-flooding waters. The slopes of flooding curves indicate the rate of storage increase (or decrease) in specific mines, although due to the complex nature of mine water mass balance, this rate is generally not amenable to simple interpretation and also reflect mine-floor geometry. Such hydrographs may indicated changes in pumping conditions, directions and fluxes of barrier leakage, changes in the latter as flooding proceeded, and effectiveness of pumping mitigation. Inflection points in flooding curves can indicate increases in barrier leakage due to a pool reaching barrier cut-throughs, changes in pumping rates, or, in one case, partial breaching of a barrier by intentional use of borehole explosives. Leveling off of flooding curves may indicate pools spilling into unflooded adjacent mines, onset of pumping control, or convergence of one or more mine pools at a common control elevation. This type of information is crucial in assessing progress of flooding and ultimate success of mine-water control efforts.