Which is NOT a solid-phase method of bioremediation? A. combining soil with fertilizers, oxygen, and water in a bioreactor B. spreading soil in thin layers on concrete pads to allow evaporation of contaminants, or draining away of contaminants as leachate C. adding bulking agents and fertilizers to degrade household wastes D. using fans and piping systems to move large volumes of air over piles of soil removed from a contaminated site .