Fred Hawkins, Jr was the first (and so far only) commissioner to respond to my email. The information he provided is below:
Osceola County does not regulate the JED landfill in Holopaw. This is done by State of Florida DEP and Federal EPA. They are the governing regulatory agencies for what materials can be disposed of at the facility, test monitoring and oversee landfill cell construction.
Ash is considered a Special Waste as well as Sludge, Contaminated Soil and bio solids, all of which have the State and Federal approval to be disposed of in a class 1 facility which the JED landfill in Holopaw is. The landfill is double composite geothermal constructed and is the best place for disposal of materials such as these according to DEP. The landfill also has test monitoring wells in and around the facility that are monitored by DEP and EPA.
The JED landfill has been accepting these materials since it opened in 2004. I encourage you to contact DEP in Orlando which is the local office that has jurisdictional oversight of the JED landfill.