The USEPA has established RCRA limits for the amounts of toxic metals that can leach into soil and groundwater. Materials that exceed the limits of the TCLP (Toxic Characteristic Leaching Procedure) or the SPLP (Synthetic Precipitation Leaching Procedure) are considered hazardous waste and must be disposed of accordingly. 

Ash that is heavily treated with Calcium, while containing substantial amounts of toxic metals, will demonstrate a substantial decrease in leachable metals. Stabilized ash may be used in soil stabilization without the danger of unconfined metals leaching into the adjacent soil or contaminating the groundwater.