Monitoring suspended sediment plumes by optical and acoustical methods with application to sand capping

There is a need to rapidly survey plumes of suspended sediment and to deter mine the quantity and transport of disturbed material that might arise from industrial and remedial activities in lakes and harbours. The example of s and capping of contaminated bottom sediments is used to illustrate the meth odology. Capping of contaminated bottom sediments is one strategy for immob ilizing contaminants. In a pilot-scale project, a 0.34 m thick cap of clean sand was deposited over a one hectare area in Hamilton Harbour. The object ive of this study was to determine if in-place sediments could be disturbed by the capping operation. In the first of three approaches, the suspended sediment plumes created during the capping operation were monitored for evi dence of suspension of bottom materials with underwater acoustic and optica l profilers and other moored instruments. In-lake calibration of the instru mentation was based on the collection of over 300 grab samples. Three-dimen sional rendering of a dense network of acoustic backscatter profiles reveal ed that there was no evidence that bottom sediment was resuspended. The den sity current flowing downslope close to the bottom caused by the capping ma terial was examined and found too weak to erode bottom sediments. Finally, a quantitative estimation of the amount of sediment suspended in the plumes indicated little evidence for resuspension of in-place sediments. The meth odology developed could also be applied to estimate the concentration and q uantities of contaminants in sediments suspended by other remedial activiti es such as dredging.