Water Quality Effects of a Dredging Disposal Area

The effect of the settling-basin concept on the water quality associated with a typical disposal site for polluted maintenance dredgings, and the fate of pollutants during a typical dredging and disposal cycle were determined between Aug.20, 1972 and Dec.20, 1972 in Toledo, Ohio. Over 100 samples of slurry influent, overflow effluent, ground water, ambient river water, bottom sediments, and material from the hopper bins and overflow waters were collected and analyzed for standard physical, chemical, and microbiological parameters. It was concluded that only a small fraction of the pollutants are discharged via the overflow weir into the ambient river water; this is attributable to the fact that the polluting substances tend to associate with the solid particles, which settle out of the suspension and are retained within the diked enclosure. The water quality of the effluent resembled that of the ambient river water used as a carrier to pump the dredgings in slurry form from the hopper dredge into the disposal area.