This study is based on using available published data on nutrient enrichment of U.S. surface waters; EPA and state nutrient control guidance@ policy@ and water quality standards; prior analysis performed for API by a third-party consultant; petroleum refinery effluent quality data from the EPA Integrated Compliance Information System/National Pollutant Discharge Elimination System (ICIS-NPDES); and permit data collected from the files of the Texas Commission on Environmental Quality (TCEQ).