An update on the winding ridge demonstration project for the beneficial use of CCBs to reduce acid formation in an abandoned underground mine

摘要

The Maryland Department of Natural Resources Power Plant Research Program (PPRP) and the Maryland Department of the Environment Bureau of Mines (MDE) have undertaken the Western Maryland Coal Combustion By-Products (CCB)/Acid Mine Drainage (AMD) Initiative. The Initiative is a joint effort with private industry to demonstrate the beneficial application of CCBs to create flowable grouts for injection into underground mines to reduce the formation of acidity (i.e., AMD). The Initiative commenced in 1995 with the Winding Ridge Project, which is its first demonstration project of this technology. For this project, 5,600 cubic yards of CCB grout were injected into the Frazee mine in 1996. The grout consisted of 60 percent FBC product, and 20 percent Class F fly ash and FGD product, mixed with mine water. Over the course of the project, an extensive set of water quality data has been generated. Water quality monitoring started prior to grout injection in 1995, and continues through the current time. The purpose of this paper is to present the key findings of post-injection monitoring of the mine discharge water quality. Post-injection monitoring shows that there have not been any significant increases in AMD-related parameters or trace elements in themine water other than short-term or transient water quality changes immediately after injection. During this transient period, mine discharge showed elevated levels of iron, aluminum, total acidity and lower pH, as well as certain trace elements. Thesechanges are attributed in part to flushing acid waters from the mine during injection. About 1 year after grout injection, iron, aluminum, total acidity and trace element concentrations and loadings dropped to levels comparable to or below pre-injectionconditions. pH has also trended subtly upward over this time. Calcium and sulfate levels have been elevated since injection indicating some grout dissolution. Since grout cores recovered from the mine show that the hardened grout is intact and competent,and has retained its strength and low permeability, any dissolution appears to be limited to grout surfaces exposed to or in contact with acid mine water.