An Assessment Of Water Quality Impacts Of Maintenance Dredging On The Upper Mississippi River In 1978

In connection with the 1979 maintenance dredging season, the Corps of Engineers, St. Paul District, investigated the water quality impacts of hydraulic and clamshell dredging operations at five selected sites on the Upper Mississippi River. Turbidity values and suspended solids were monitored at all sites, and selected chemical parameters were monitored at two hydraulic dredging sites. At most sites, dredging and disposal operations produced minor and localized changes in water quality. No statistically significant increases in chemical parameters were noted due to hydraulic dredging operations. However, effluents from the disposal area did cause some elevations of heavy metals (cadmium, lead, nickel, zinc, copper, chromium) and total ammonia. None of the chemical parameters tested exceeded their maximum permissible level proposed by Federal Water Quality Criteria. The five monitoring studies generally indicated that rapid settling and dilution occurred near and downstream of dredging and disposal operations.