Legal Authority for CWA Analytical Methods
Section 301(a) prohibits the discharge of any pollutant into navigable waters except in compliance with the CWA (typically implemented in an NPDES permit issued under section 402).
Section 304(h) requires EPA to establish test procedures to measure pollutants in Clean Water Act programs, such as NPDES.
Section 501(a) authorizes EPA to prescribe such regulations as are necessary to carry out functions under the Act.
EPA generally has codified the approved test procedures (analytical methods) in the Code of Federal Regulations at 40 CFR Part 136. These methods are sometimes referred to as "wastewater", "Part 136", or "304(h)" methods. Some approved methods may also be found at 40 CFR Parts 401 through 503 (Effluent Guidelines and Biosolids regulations).