This amendment to the Guidelines Establishing Test Procedures approves the use of an additional procedure for the determination of chlorinated pesticides and polychlorinated biphenyls (PCBs) in wastewater by adding appropriate citations to Tables IC and ID and by amending the incorporation by reference section of the regulation accordingly. The method differs from other approved methods in that it incorporates a disk of octadecyl-bonded silica enmeshed in a matrix of inert polytetrafluoroethylene (PTFE) fibrils for extraction of the analytes. The precision and recovery for the chlorinated pesticides and PCBs using this technique are not substantially different from those obtained using the liquid-liquid extraction technique already approved. Use of approved analytical techniques is required whenever the waste constituent specified is required to be measured for: an NPDES permit application; discharge monitoring reports; state certification; and other requests from the permitting authority for quantitative or qualitative effluent data. Use of approved test procedures is also required for the expression of pollutant amounts, characteristics, or properties in effluent limitations guidelines and standards of performance and pretreatment standards, unless otherwise specifically noted or defined.