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This document contains direction developed solely to provide internal guidance to U.S. Environmental Protection Agency (EPA) personnel. EPA retains the discretion to adopt approaches that differ from this guidance on a case-by-case basis. The guidance set forth in this document does not create any rights, substantive or procedural, enforceable at law by a party to litigation with EPA or the United States. The use of mandatory language such as “must ” and “require ” in this guidance document reflects sound scientific practice and should not be construed to create any legal rights or requirements. The use of non-mandatory language such as “may, ” “can, ” or “should ” in this guidance does not connote a requirement but does indicate EPA’s strongly preferred approach for validating and peer reviewing EPA methods prior to publication for general use. References within this document to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily imply its endorsement or recom-mendation by EPA. Neither EPA nor any of its employees, makes any warranty, expressed or implied, nor assumes any legal liability of responsibility for any third party’s use, or the results of such use, of any information, apparatus, product, or process disclosed in this manual, nor represent