Injection of fixated scrubber sludge into abandoned coal mines

Fixated scrubber sludge (FSS) was injected into an abandoned underground coal mine in southwestern Indiana. The project was undertaken to evaluate using FSS to control mine subsidence and reduce acid mine drainage. Preinjection laboratory testing included characterization and analysis of the effects that the mine environment has on the FSS. Bench scale testing determined the composition for optimum flow, minimization of free water, and physical characteristics. A total of 16,351 cubic yards of FSS was injected over an eight-week period in late 1994. This resulted in filling about five acres of the mine. The injected FSS was sampled at six and at nine months after injection. Unconfirmed compressive strengths were generally from 100 to 200 psi. The hydrogeologic environment surrounding the mine was monitored by sampling ground water over a six month period prior to injection and then quarterly for one year after injection. There were some changes in the concentration of chemical parameters in the mine pool water, particularly in close proximity to injected FSS, but no significant changes in ground water chemistry surrounding the mine.