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|Title:||Evaluation of hopper loading and overflow for Saginaw River, Michigan|
|Authors:||United States. Army. Corps of Engineers. Detroit District.|
Dredging Operations Technical Support Program (U.S.)
Palermo, Michael R.
Randall, Robert E., 1940-
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: The US Army Engineer District, Detroit, maintains a navigation channel in the Saginaw River near Saginaw, MI. The sediments in some reaches contain metals and polychlorinated biphenyls (PCBs). A hopper dredge is normally used, and overflow of the hopper is sometimes practiced to increase the load of solids for transport to the disposal area. The Detroit District has initiated a policy of no overflow in reaches of the channel where sediment PCB concentrations exceed 10 mg/kg (dry weight). However, there is concern over the possible impact of overflow from hopper dredging operations when sediments are dredged from other reaches of the channel where sediment PCB concentrations are less than 10 mg/kg. This report describes an evaluation of hopper loading and overflow characteristics on the Saginaw River conducted during August and September 1987. The study was designed to evaluate the effectiveness of increasing the hopper load during overflow and to determine the physical and chemical characteristics of the overflow for the.Saginaw project. Three hopper loads were monitored and sampled for the study during routine maintenance dredging operations -- one in an upstream reach (Area I) and two in a downstream reach (Area II). The loading characteristics of the dredge before and during overflow were monitored using onboard instrumentation. Samples of inflow, hopper contents, and overflow were collected during filling and overflow and analyzed for both physical and chemical characteristics. Samples were also taken in the channel water column to define the plume characteristics for both overflow and nonoverflow conditions. Since sediments in the upper reach of the project were known to have very low levels of contamination, chemical testing was limited to samples collected in the lower reach. A final gain in hopper load of 22.5 percent was realized during an overflow period of approximately 90 min for the load monitored in Area I, No gain was realized for an overflow period of approximately 6 min for the load monitored in Area II. Suspended solids data for the loads monitored indicate that approximately 40 percent of the solids was retained during overflow. Grain size data indicate some retention of coarser particles in the hopper. Retention of metals and PCBs in the hopper generally corresponded to that of solids. Concentrations of solids in both the overflow and nonoverflow plumes were reduced to near-background levels within 20 min of the passage of the dredge. Concentrations of chemical parameters were reduced to near-background levels in a similar manner.
|Appears in Collections:||Miscellaneous Paper|