GEOPHYSICAL MAPPING AND SUBSURFACE INJECTION FOR TREATMENT OF POST-RECLAMATION ACID DRAINAGE

Abstract

Post-reclamation acid discharge has haunted abandoned mine lands reclamation programs and the mining industry reclamation efforts. Many mine sites have been reclaimed, as mandated by regulations, but continue to generate acid. Such sites represent perpetual treatment problems for operators and, in the case of bond forfeitures or abandoned mine reclamation projects, they represent sources of perpetual surface and groundwater degradation. Post-reclamation discharge occurs when the Thiobacillus ferrooxidans bacteria, not destroyed prior to soil cover in the reclamation process, continue to thrive, even in a supposedly anaerobic environment. A post-reclamation remediation system utilizing subsurface injection of sodium hydroxide and an anionic surfactant offers a two phase integrated technologies approach. In Phase 1, the site is characterized by geophysical mapping with (1) electromagnetic terrain conductivity meters to determine locations of subsurface aquifers, and (2) proton processing magnetometers to delineate zones of pyritic oxidation in the subsurface environment. Infiltrometers are also used to determine permeability which influences pressure requirements and distance between wells. Site conditions and water analyses help quantify requirements for injection of sodium hydroxide and bactericide. Phase 2 involves drilling two sets of injection wells; the first into the acidified water table for injection of 20% sodium hydroxide solution to neutralizemore » existing acid water, and the second into the acid producing material for injection of a 20% sodium hydroxide solution to neutralize existing acid salts, followed by a 2% solution of bactericide. The sodium hydroxide is injected to neutralize existing acid which prevents future acid generation. Results from a site in Pennsylvania, USA, which was treated in this manner are reported.« less