ESTABLISHING HYDRAULIC CONNECTION BETWEEN FLOODED UNDERGROUND COAL MINES USING CONTINUOUS MONITORING OF TRANSIENT SURFACE FLOOD PULSES

Recent research assessing the feasibility of using coal-mine water as a supplement for a public water supply in Greenwood, Arkansas, provides a strong case study illustrating the application of continuously monitoring water levels in contiguous mines to establish a hydrogeologic connection between them. Selected wells and strip pits in the Greenwood #2 mine and Fidelity mine were equipped with transducers and recording temperature probes. The magnitude and timing of different water-level responses provides a means to document the nature and degree of interaction between different parts of the mines and surface hydrologic features. Areally similar signals, occurring coincidentally with the onset of precipitation measured by tipping-bucket rain gages, are indicative of widespread precipitation loading over both mines. The variable perturbations in the water levels in both mines after storms are another matter, however. Ground-water level responses are nearly coincident, and their cause has been established as pressure loading owing to systematic releases from Greenwood Reservoir into Vache Grasse Creek, a surface feature that overlies only the Greenwood #2 mine. The dam has been equipped with an extension that provides added storage to Greenwood Reservoir. The extension automatically retracts and releases a wall of water when reservoir level reaches a critical, potentially hazardous level. Runoff from large precipitation events, therefore, shows a recession with increasingly prolonged pulses as the storm runoff is dissipated. Inasmuch as Vache Grass Creek does not overlie Fidelity Mine, the near-coincident water-level rises observed from wells in Fidelity are interpreted to be transmitted as pressure waves through a failed dam between the mines that previously was sealed. Supplemental data, including eyewitness accounts of flow from the mines and water quality are consistent with interpretations based on the transient surface-flood pulses.