Developing Methods for Collecting Source Water Baseline Biological Characterization Data

National Pollutant Discharge Elimination System permittees that have cooling water intake structure (CWIS) flows generally greater than 125 million gallons per day must evaluate entrainment of aquatic biota, predominantly icthyoplankton.  Clean Water Act §316(b) directs existing facilities to characterize the biological community near the CWIS for a variety of parameters.  In the event that historically pertinent data are unavailable, it becomes necessary to characterize baseline biological data from the source water concurrently with entrainment sampling at the CWIS.  Ecological and economic impacts from entrainment should be based on population-level models developed using icthyoplankton stocks from the source water and mortality rates measured in the field.   Source water characterization requires a combination of sampling methods including split-beam hydroacoustic surveys, larval light traps and plankton trawls.  Hydroacoustic surveys provide icthyoplankton density and behavioral data, and traps and trawls provide taxonomic and life-stage verification data. These data determine when entrainment sampling should be conducted at the CWIS, and ensure sampling occurs during species-specific spawning events and subsequent icthyoplankton blooms.  In addition, standardizing these methods yields a cost-effective process for quantifying ecological and economic impacts in areas with well-defined source water reservoirs and multiple CWIS.