In 1994 an EPA sponsored field scale investigation was conducted to evaluate the effectiveness of using coal combustion byproducts (CCBs) for in situ treatment of acid mine drainage—coined alkaline injection technology (AIT). In 1997, 379 tonnes of fluidized bed combustion (FBC) ash were injected into an abandoned coal mine in eastern Oklahoma with positive results; however, the amount of alkalinity added to the system was limited and resulted in a 15 month treatment duration. In December 2001, 2,225 tonnes of FBC ash were injected (under a CBRC grant) into the same mine as part of a field demonstration scale project.
Post-injection monitoring continued for 24 months. During this period the mine chemistry progressed through a series of chemical changes that manifested as states or “treatment phases.” The mine system appeared to be in the midst of reestablishing equilibrium with the partial pressure of CO2 in the mine headspace. Alkalinity and pH appeared to gradually increase during this transition. As of November 2005, the pH and alkalinity were 6.8 and 165 ppm, respectively. Metal concentrations were significantly lower than pre-injection levels, but iron and manganese concentrations were increasing (to roughly 50 ppm and 2 ppm, respectively, as of December 2004). Aluminum, nickel, and zinc were less than pre-injection concentrations and did not appear to be increasing.
Additional monitoring is needed to fully evaluate the treatment effectiveness. The AIT project has been under study since 1994 (first CCB injection occurred in 1997). Monitoring has been conducted for roughly 11 years with over 2 years of pre-injection monitoring for background evaluation. Consequently, this project has the secondary objective of evaluating the impact of CCBs on the ground and surface water system. The monitoring information could be used evaluate the treatment and environmental impacts.
Dr. Geoffrey A. Canty
CC Environmental
PO Box 1292
Norman, OK 73070
OR 155 Triad Village Drive
Norman, OK 73071
405-321-8181 Telephone
405-307-9290 Fax
ccenvironmental@sbcglobal.net