Patterns in Impingement and Entrainment Survival: What to Expect in Verification Monitoring for the New §316(b) Regulations

Prior studies of impingement (80 at 37 facilities) and entrainment (21 at 7 facilities) survival were analyzed for patterns that may inform decisions on complying with the new §316(b) regulations. Failure Time Analysis was used to describe the temporal pattern of mortality for impinged fish, crabs, and shrimp.  All three groups were found to consist of hardy and more sensitive groups of species.  Ristroph-type modifications increased the survival on conventional traveling screens, dual-flow screens, and angled screens.  Impingement survival was modeled as a function of screen type, hardiness category, and waterbody type. 

Due to the concentration of entrainment survival studies in northeastern estuarine sites, the number of species examined in detail was relatively low. The studies examined predominantly post yolk-sac larvae, which separated into three distinct patterns of hardiness based on intake survival: relatively low initial survival followed by little or no survival at subsequent examination times, moderate levels (0.4 to 0.7) of survival, and relatively high survival (above 0.7) at the intake.  Intake survival correlated with actual estimates of through-plant survival in most cases.   Where the same species were observed for entrainment and impingement, hardiness to the two types of interaction with cooling water system appeared to be consistent.