A Pilot Study on Effects of Hydraulic Dredging and Disposal on Water Quality of the Upper Mississippi River (July 1976). GREAT I Water Quality Work Group
CORPS OF ENGINEERS ST PAUL MN ST PAUL DISTRICT
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A pilot study was designed and implemented to monitor the water quality impact of dredging and disposal using a variety of sampling techniques. The study took place at river mile 827 on the Upper Mississippi River immediately downstream of the Minneapolis-St. Paul metropolitan area Grey Cloud Island. Samples of undistributed predredge bulk sediments and postdredge plume water were examined for physical, chemical and bacteriological parameters. Concentrations of contaminants in sediment samples were apparently influenced by seasonal fluctuation in flow, sediment deposition and water quality. Bottom sediments revealed high concentrations of several contaminants in comparison to other sediment studies conducted at the same locations. Most parameters exhibited an increase in concentration from above to below the dredging and disposal operation during the two days of monitoring. Ambient fluctuations in river water were, in many cases, greater than impacts caused by dredging and disposal. Physical and bacteriological parameters returned to background concentrations within 1.3 kilometers 0.8 mile downstream of the disposal discharge. Chemical parameters normally returned to background within a much shorter distance. Impacts were generally localized due to the sorptive capacity of rapidly settling resuspended sediment particles and dilution. Most parameters, especially the suspended form of metals, showed a high positive correlation with suspended solids and other physical parameters.
- Hydrology, Limnology and Potamology
- Civil Engineering