A power plant located in North Texas was unable to meet the permitted effluent limitations aluminum and lead contained in its Texas Pollutant Discharge Elimination System (TPDES) permit for the discharge of once through cooling water. Since there were not industrial activities performed by power plant that potentially could be a source of aluminum and lead, it was assumed that the concentrations reported to be present in the once through cooling water were associated with background concentrations. Zephyr suggested performing an surface water quality investigation in accordance with Texas regulations that provides an exclusion for the need of water quality-based effluent limits (WQBELs) in cases where it can demonstrated that no measurable increase in the pollutants of concern occur in the discharge of once-through cooling water. A Work Plan for this investigation was prepared in accordance with State and Federal guidelines and was approved by the TCEQ. Following the collection and statistical analysis of analytical data collected in accordance with the approved Work Plan, Zephyr was able to demonstrate to the satisfaction of the TCEQ that the metals were associated with background concentrations. A permit amendment was submitted to the TCEQ to delete monitoring requirements for aluminum and lead. The permit amendment was approved.