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Section 316(b) Entrainment and Impingement Services

CLEAN WATER ACT AND U.S. ENVIRONMENTAL PROTECTION AGENCY SECTION 316(b) IMPINGEMENT STUDY

Electric Power Research Institute

Under contract with the Electric Power Research Institute, EA conducted impingement abundance monitoring at 15 Ohio River power plants in response to the Clean Water Act and U.S. Environmental Protection Agency Phase II Section 316(b) rule.  The purpose of this study was to identify factors affecting impingement rates.  Covering nearly 900 river miles, the scale of this study was unprecedented and EA performed 550, twenty-four-hour impingement sampling events over a 2-year period.  Due to the breadth of the study and its vast data collection requirements, EA drew on its experience to diligently control program costs while ensuring data integrity.  EA accomplished this by reducing the required sampling frequency and improving the precision of the annual impingement estimates by applying a model-based study design based on historical impingement data.  In addition, EA substantially reduced mobilization costs by establishing two field offices and stationing 15 environmental professionals along key stretches of the river.  Results demonstrated similarities in species composition, size distributions, and seasonal patterns of impinged fish consistent with studies conducted nearly 30 years earlier.  Dramatic annual differences in impingement rates indicated that impingement is largely a function of the recruitment levels of juvenile gizzard shad, threadfin shad, and freshwater drum, which fluctuate widely and unpredictably. 

The Section 316(b) impingement study also showed that most physical variables had little or no effect on impingement rates.  Water temperature was identified through multiple regression analyses as the most important physical variable, with impingement tending to increase during the winter.  Actual pumping rate during sampling events—the only factor evaluated that is under the direct control of the participating power plants—was determined to be one of the least important factors affecting impingement rates.  The study provided a robust data set that allowed a statistical evaluation of factors affecting impingement rates, the results of which were published in a peer-reviewed journal (North American Journal Fisheries Management 30:1149-1176).