Flocculant settling above zone settling interface

A recently developed procedure for predicting the suspended solids (SS) concentration in the effluent from confined disposal areas for dredged material was refined to allow prediction of the effluent SS concentration for the disposal of saltwater sediments. The dredged material normally settled as a slurry by zone settling, forming a clarified supernatant in the disposal area. Settling tests were conducted on sediments from Mobile harbour, Black Rock harbour and Yellow creek using the modified column test. The effect of initial supernatant SS concentration, depth of averaging on concentration remaining and initial slurry concentration on sediment settling are summarized. The settling behaviour of fine particles initially remaining in the supernatant was determined. Procedures were developed to predict the effluent concentration as a function of retention time and other relevant operating conditions. Based on comparisons of column predictions and measured field data, settling efficiency factors ranging from 1.5 to 2.5 conservatively predicted effluent SS concentration.