Statistical Design Basis for Submerged Diffuser

A comparison is made among discharge criteria for various atmospheric and aquatic emissions. The dependence of effluent plume size on water levels, ambient temperatures, and drift currents was empirically determined from model simulation. Predictions of the effluent plume size frequency distribution were made: (1) Assuming the parameters are independent random variables; and (2) using a time series of lake levels, temperatures, and currents. The second method predicted less frequent occurrence of large plumes. It is concluded that: (1) Statistical description of predicted thermal plumes represents a more realistic evaluation of environmental impact than prediction for a “critical” condition; (2) readily available site data can be utilized to make statistical predictions of the effluent plume size for proposed outfalls; and (3) the effectiveness of design changes can be statistically evaluated and interpreted as frequencies with which given thermal criteria may be contravened.