The feasibility of abating acidic discharges from an abandoned underground coal mine by in situ neutralization (alkaline injection) within the mine pool has been investigated by the U.S. Bureau of Mines at a site within Keystone State Park, near Latrobe, Pennsylvania, (USA). Maps of the mine entries and mine floor elevations, mine discharge flow rates, precipitation records, monitoring well water levels, and water quality analyses were used to characterize the mine pool flow system. At this site, the original mine entries were generally found to be intact and the mine pool piezometric surface was approximately horizontal. The mine pool flow is believed to occur mainly through the open entries, with negligible laterial flow through the overlying strata and coal pillars. Chemical tracer tests indicated that flow through mine entries, with negligible lateral flow through the overlying strata and coal pillars. Chemical tracer tests indicated tht flow through mine entries is probably not uniform and that preferred flow paths through unmonitored entries may exist. On May 23, 1990, approximately 7,570 l of 25-pct sodium hydroxide solutuion (1,890 kg of naoh) were injected into an upgradient portion of the mine pool. Water-quality analyses indicated that the alkaline solution appeared to have migrated away from the injection wells within 2 months after treatment, but no significant change in the discharge quality was noted after 7 months.
Proceeds 2nd Int'l. Conf. on Abatement of Acidic Drainage, Quebec, Canada, V. 1, PP. 69-89