Alkaline injection technology: Field demonstration

In December 2001, 2225 tonnes of fluidized bed combustion (FBC) ash were injected into an abandoned coal mine in eastern Oklahoma. Post-injection monitoring continued for 24 months, during which the mine system appeared to be reestablishing equilibrium with CO₂ in the mine headspace. Alkalinity and pH gradually increased, and as of December 2003 were roughly 65 ppm and 7.3, respectively. Metal concentrations were still significantly lower than pre-injection levels, but iron and manganese concentrations had increased from non-detect levels shortly after injection to roughly 30 ppm and 1.25 ppm, respectively. Aluminum, nickel, and zinc were less than pre-injection concentrations and did not appear to be increasing (roughly <PQL, 0.02 ppm, and 0.1 ppm, respectively). Arsenic and boron were not identified in concentrations that were of concern for protecting freshwater aquatic communities; however, selenium was well above the criterion continuous concentration and the maximum contaminant level. There were obvious improvements observed in the receiving environment—benthic habitat recovery and the return of fish species. However, additional monitoring is needed to determine the duration of the treatment and to evaluate the applicability of the treatment technology.