An Analysis of the Design Requirements Affecting Water Discharges through Strata from Below Drainage Abandoned Mines

摘要

The mining industry is required to prevent post-mining discharges through appropriate design and engineering considerations. The state and federal governments are responsible for making sure standards are maintained and followed. In recent years, both the mining industry and the government regulators have focused on the ability of strata barriers to prevent discharges from mine pools into surface waters. Strata barriers comprise the rock layers between the coal mine pool and the overlying stream; however, in Northern Appalachia, the strata can contain iron and acid producing geochemistries. As a result, water that comes into contact with these rocks has the potential to become impaired. The strata beneath stream valleys are also generally known to have increased frequencies of fractures in this region (Ferguson, 1967). The hydraulic head that is produced by the mine pool provides a discharge potential through surrounding layers of rock. When the mine pool elevation is greater than the lowest elevations on the surface, a “net head” is placed on the barrier which creates discharge potential. As a result, it is important to understand the movement of mine pool water through the strata above abandoned mine workings and establish design factors to prevent potential discharges into streams.udSeveral below drainage strata barriers were analyzed in this study. The primary objective is to determine how geology, overburden properties, hydraulic head, and mine layout impact the ability of abandoned mine workings below drainage to contain a mine pool and prevent discharges after production has concluded. Specific conditions are monitored to distinguish the primary design differences between barriers that discharge water through overlying strata and successful ones that prevent discharges to the surface or into streams. Multiple case studies in western Pennsylvania are analyzed, providing examples of situations where strata barriers are involved in post-mining drainage potential where mine pool elevations exceed the lowest elevations at the surface. Many factors are examined to determine the conditions associated with successful design properties that minimize discharges. Standards for optimal mine design are presented via analysis of design characteristics and associated potential discharges. Ultimately, this work clarifies the factors responsible for successful and unsuccessful designs of strata barriers that prevent a discharge to surface waters.ud