MILL RUN: RECOVERY OF A SMALL STREAM IN WESTERN MARYLAND USING LIMESTONE SAND APPLICATION AND PULSE LIMESTONE BED TECHNOLOGY

摘要

Mill Run is a small, fast flowing, mountain stream located in western Allegany County, Maryland. Its headwaters support a population of wild brook trout, while its lower half is impacted to various degrees by acid mine drainage (AMD) from three abandoned deep mines. Prior to restoration efforts, the first portion of the AMD impacted stream showed the effects of the AMD in reduced population densities and species diversity while the lower third of the stream was so severely impacted that no aquatic life--other than bacteria and algae--existed. Restoration efforts began in July 1998 by application of a limestone sand mixture into the stream at various locations. Due to funding issues the limestone sand application project was reduced to only one partial application in 2001 and no application in 2002. In December 2000, construction of a second remediation project, an experimental purge diversion well, was initiated. The construction of this system was completed and operation began on December 17, 2002. The well uses limestone sand and re-circulates carbon dioxide gas to increase the dissolution of the sand. The hydraulic head pressure of the AMD is used to operate the system. In addition to these two abatement projects, a preliminary characterization study at the third mine site was completed in December 2000. The study evaluated various AMD abatement technologies with respect to the mine's characteristics. Funding to design and implement an abatement project at this site will be sought from available sources in the future. The results of the two abatement projects completed to date can be seen at sample Station #4, which is located near the mouth of Mill Run. The pH at this station has increased by approximately 2 units, the water is now alkaline and dissolved metals have been reduced by over 75 percent. This paper discusses the AMD abatement projects, their impact on the water quality of Mill Run, and the subsequent and remarkable biological response to implementation of the first of the three projects.