Hazardous Waste—A solid waste, or combina- tion of solid wastes, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may either cause, or signifi- cantly contribute to, an increase in mortality or an increase in serious irreversible or incapacitating reversible illness; or pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed.