Approach to ecological assessment of power-plant-intake (316b) related issues: the Prairie Island case

Assessment approaches and strategies useful in addressing important issues in section 316(b) of the 1972 Federal Water Pollution Control Act are illustrated in this report through the analysis and evaluation of the Prairie Island Nuclear Station 316(b) data base. The main issues in 316(b) demonstrations, cooling water intake operation and location, involve determining the impacts of entrainment and impingement. Entrainment impacts were addressed by applying the equivalent adult approach and correcting for inherent biases and by determining the through-plant survival of zooplankton. An assessment of impingement impacts was made by comparing for each of various species the number of fish impinged to estimates of population size. Densities of plankton and fish were compared between the intake area and an alternate area to determine if the location of the present intake minimizes impacts. No definitive conclusion relative to the best location of the intake could be made because of high year to year variability in the data and the differential dominance of trophic groups between areas