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 for water monitoring. These test procedures must be used in applications for permits and for reporting under the National Pollutant Discharge Elimination System (NPDES) program unless use of an alternate procedure is approved by a Regional Administrator or a state with an EPA-approved NPDES permit program. The regulation would also revise, clarify, and correct errors and ambiguities in existing methods.