Waste Oil Heater Forum - Your definitive source for burning waste oil for heat.

Can anyone direct me to, or inform me of, any governmental (USA) regulations regarding the disposal of the ash from waste oil heaters?  I am currently burning used engine oil in a professionally manufactured heater consuming approximately 2000 gallons per season.  It is generating probably 10 gallons of ash or residue per season.  What is the proper/environmentally friendly/legal method of disposing of this bi-product?  Does anyone know of any documented health risks.  I guess this is rarely addressed since the range of possible contaminants is endless.