The Environmental Protection Agency (EPA) Regulation 503 sets the parameters for disposing of sludge through land application.  Regulation 503 was enacted in 1993 and outlines the maximum amounts of potentially harmful or toxic materials (heavy metals and biological organisms) sludge may contain. Regulation 503 excludes consideration of organic compounds such as polychlorinated biphenyls (PCBs). Regulation 503 is self-enforced.