Association of Battery Recyclers v. EPA addresses MGP exemption from the Federal Hazardous Waste Program. On April 21, 2000 the United States Court of Appeals held unanimously that EPA did not properly define "solid waste" and that EPA's treatment standards for MGP waste were lawful. In order to determine whether a solid waste is toxic, the EPA adopted a test called the Toxicity Characteristic Leaching Procedure (TCLP). In the Phase IV Rule the EPA used the TCLP as the test for determining the toxicity of mineral processing wastes, including MGP waste. The court held that EPA failed to justify application of the TCLP to MGP waste and, therefore, granted the petition for review in part and vacated the Phase IV Rule insofar as it provides for use of the TCLP to determine whether MGP waste exhibits the characteristic of toxicity.