1999 Progress Report: Evaluation of Natural Amelioration of Acidic Deep Mine Discharges for Watershed RestorationEPA Grant Number: R825794
Title: Evaluation of Natural Amelioration of Acidic Deep Mine Discharges for Watershed Restoration
Investigators: Dzombak, David A. , Aljoe, William W.
Current Investigators: Dzombak, David A.
Institution: Carnegie Mellon University
EPA Project Officer: Packard, Benjamin H
Project Period: June 1, 1998 through May 31, 2001 (Extended to September 30, 2001)
Project Period Covered by this Report: June 1, 1998 through May 31, 1999
Project Amount: $610,484
RFA: Ecosystem Restoration (1997) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Hazardous Waste/Remediation , Land and Waste Management , Ecosystems
Objective:The overall goal for the project is to identify the hydrologic and geochemical factors responsible for improvements over time in the quality of water discharges from abandoned deep mines. A related goal is to evaluate the effects of mining methods and abandoned mine management practices on long-term changes in mine water quality.
The project involves study of a set of mine water discharges associated with abandoned, interconnected mines in the Uniontown-Connellsville area of Western Pennsylvania. Almost all the deep-minable coal was removed from this area prior to 1970, and an extensive baseline study of mine discharges in the area was conducted in 1974?1975 in conjunction with Operation Scarlift (Scarlift). New water quality monitoring was initiated in July 1998 at 21 of the abandoned mine drainage (AMD) sites studied previously and will be continued for 2 years. The degree of mine water quality improvement since 1974?1975 is being assessed. The local environment for each discharge also is being studied to relate observed changes in mine water quality to factors such as the extent of mine flooding and the chemistry of the rock overlying the mined area. The Pennsylvania Department of Environmental Protection (PADEP) is collaborating with the project.
AMD Monitoring?Uniontown Syncline Basin. In year 2 of the project, flow and water quality monitoring was continued at the 21 selected AMD discharge locations in the Uniontown Syncline, Fayette County, Pennsylvania. The syncline plunges from the north and from the south creating a canoe-shaped coal basin. The Youghiogheny River (Yough) splits the basin into two distinct regions: the northern portion and the southern portion. The mines in the northern portion are low-cover mines developed updip (upgradient) from the surface entries, which has resulted in freely draining discharges and unflooded mine voids. Deep mining in the northern portion of the basin was complete by the 1930s, and the discharges have existed since that time. The mines in the southern portion cover a larger area and include mine voids with up to 600 feet of overlying soil and rock (overburden). The deep mines were developed either downdip from the surface entries or updip from deep shafts, resulting in flooded mine voids. Deep mining in the southern portion was mostly completed by 1960, and the discharges began subsequently.
Field Site Characterization Mapping. Mine maps for the Uniontown Syncline have been digitized and this information used to develop a map of coal-in-place barriers for the interconnected mine system in the basin. This map is being utilized to help define the hydraulically separated mine areas for minewater flow assessment. In addition, topographic and land use maps for the study area have been collected and used to identify watershed boundaries and runoff characteristics for the hydrologic/hydraulic modeling effort. Finally, information on soil and rock overlying the main coal seam has been collected and used to construct subsurface profiles of overburden thickness. Establishment of overburden thickness has assisted estimation of water recharge to the mine network.
Field Data Evaluation. Preliminary interpretations of the field data have been undertaken. Comparison of the mine water quality data collected in this study and in Scarlift indicates that flooding has an important role in the change of AMD from acid to alkaline. Discharges from flooded mines were either alkaline in the Scarlift study, or have become alkaline since Scarlift. A substantial decrease in iron and sulfate concentrations occurred between 1974 and 1975 and between 1998 and 1999. The discharges from the unflooded mines remained acidic over the same period, but small decreases in iron and sulfate concentrations occurred. The concentrations of iron and sulfate in the discharges from the unflooded mines are surprisingly low, and were low even in 1974?1975. This indicates that another factor besides flooding, possibly exhaustion of pyrite, can bring about improvements in minewater quality. This factor and the role of overburden in long-term mine water quality change currently are being evaluated.
Hydrologic and Chemical Modeling. Full interpretation of the monitoring data will require hydraulic analysis coupled with geochemical modeling. For hydraulic modeling, a box modeling approach has been adopted in which hydraulically separated mine areas are represented as simple tank reactors. The model has been applied to describe the hydrologic and mine discharge data collected to date. For the geochemical modeling, a mechanistic model has been developed for ferrous sulfide (pyrite) oxidation that couples the rate-limited and equilibrium chemical reactions governing pyrite dissolution.