25 Pa. Code § 16.52
The Department may require WETT, under § 92a.21(d)(4) (relating to application for a permit), for any discharges covered by an NPDES permit or other activities where it is determined that the testing is necessary to assure the protection of aquatic life. Where WETT is required, the Department will use the criteria of 0.3 TUA (Toxic Units Acute) and 1 TUC (Toxic Units Chronic) design conditions and other applicable factors as a basis for evaluating test results. WETT shall be conducted in accordance with 40 CFR Part 136 (relating to guidelines establishing test procedures for the analysis of pollutants), Chapter 252 (relating to environmental laboratory accreditation), the NPDES permit, Quality Assurance Quality Control guidance issued by the Department or other protocols approved by the Department.
25 Pa. Code § 16.52