Numerical model of sewage sludge transport and deposition from the 106-mile municipal dumpsite

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A three-dimensional, personal computer based particle tracking model was developed to predict the dispersal of sewage sludge particles discharged at the 106-mile deepwater Municipal Sludge Dumpsite. The model was employed to predict sludge dispersal during two EPA current meter and sediment trap deployments: May 25-October 31, 1990 and November 1, 1990 to June 17, 1991. The sludge discharge rate and settling velocity distribution, by mass faction, were obtained from available data. Current fields were represented by integrating the observed data from the mooring sites during the deployment with historical data describing the mean spatial current pattern. Ring induced currents were described based on a solid body rotation approximation with the ring path and radius derived from satellite imagery. Model predictions compared favorably to sediment trap data both showing maximum seabed depositions downstream of the release site and decreasing rates with increasing distance. Sensitivity studies showed that model predictions were very sensitive to the particle settling velocity distribution and relatively insensitive to the horizontal dispersion coefficient. Predictions based on Dynalysis's three dimensional hydrodynamic model year long simulations for 1988 resulted in significant reductions in particulate mass fluxes at all levels compared to the case when observation data were used to define the current field. This result is consistent with the fact the hydrodynamic model substantially overpredicts the flow in the shelf-slope area.

Publication Title

Journal of Marine Environmental Engineering