- Bob Pavlowky
- Matt Pierson
The purpose of the BRLRS is to implement managed sedimentation areas where mining-contaminated sediment can be deposited during flood events and later be removed for land disposal. The project site is located along the Big River in St. Francis County, Missouri where the channel bends to the north just south of Bonne Terre and immediately below the confluence of Flat River Creek. Lead (Pb) mining operations released large quantities of mineral mining wastes into Big River and Flat River upstream of the structure between 1900 and 1972. These materials have been dispersed downstream by sediment transport processes to contaminate the Big River to toxic levels for Pb and other metals. Presently, however, there are still large quantities of contaminated sediment stored in channel bed or bar deposits that is available to move downstream over time. Removal of Pb-contaminated sediment from the channel offers an opportunity to decrease the loading rate of sediment-Pb to downstream segments along Big River.
The structure was designed by the US Army Corp of Engineers and constructed by private construction firms to remediate contaminated sediment in the Big River. It includes two main components: (1) Newberry riffle designed to locally raise base-level in the channel, decrease channel slope, and trap contaminated bed sediment behind it, and (2) excavated basin system within the floodplain on the inside of the bend to pond water and capture contaminated suspended sediment and finer bed sediment during high flows. Construction was completed this past Spring. However, the specific changes to the local topography during the construction of the structure and the final location of key design elements have not yet been documented. Further, the degree to which the structure will trap sediment and the effectiveness of the structure to reduce in-channel sediment lead levels in Big River overall has not been evaluated.
- Assess and map the “as-built” condition of the completed structure;
- Monitor periodically the condition and stability of the constructed basin and riffle as well as the natural channel and bank system within the project reach given the influence of local geomorphic and human disturbances related to structural stability, flood effects, and sediment conditions;
- Monitor and quantify the volume, properties, and geochemistry of contaminated sediment trapped behind the riffle structure;
- Monitor and quantify the volume, properties, and geochemistry of contaminated sediment deposited within the off-line basin structure; and
- Evaluate the overall structural integrity and sediment/Pb trapping effectiveness of the structure.
U.S. Environmental Protection Agency, Region VII
U.S. Environmental Protection Agency