This regulatory action would amend "Guidelines Establishing Test Procedures for the Analysis of Pollutants" at 40 CFR Part 136 to approve test procedures (analytical methods) for use by testing laboratories and others for water monitoring. These test procedures must be used to implement the NPDES program unless EPA has approved the use of an alternate procedure. This action approves new and revised versions of testing procedures approved for analysis and sampling under the CWA. The rule is expected to include primarily method revisions from voluntary consensus standard bodies and Alternate Testing Procedures that are comparable to the current methods. Generally, these changes will have a positive impact on NPDES permittees by increasing method flexibility, thereby allowing entities to reduce costs by choosing more cost-effective methods.