Environmental Effects of Overboard Spoil Disposal

Navigation channel improvements along a reach of 14 km in upper Cheasapeake Bay required that approximately 4.5 × 10⁶ m³ of silt and clay be dredged and the spoil deposited in shallow water 1000 m west of the dredging site. Biological and geological studies were performed on a 3 km test section of the planned work involving 1.3 × 10⁶ cu m of spoil deposited in shallow water (approx. 4 m depth). Bi-weekly cruises were conducted to measure total material in suspension, temperature, salinity, bottom sediment characteristics, and current velocity patterns in the anticipated area of effect. During the actual spoil disposal, continuous determinations of the distribution of suspended sediment were conducted and compared with background levels. Results indicate that measurable quantities of suspended sediment extended as far as 4 km from the disposal point, that the spoil on the bottom did not remain within the limits of the disposal area, and that dissolved nutrients contained in the spoil sediment pore-water were probably released to the environment.