Sediments which have accumulated in the Milwaukee River North Avenue urban impoundment in Milwaukee, Wisconsin over a period of more than one hundred years were investigated. After the drawdown of the water level in the impoundment, extensive investigations focused on determining sediment volume, characteristics and contamination. It was found that the accumulated sediment has a fine texture and contains higher levels of toxic metals.

Analysis of sources of sediments and sediment contamination considered the background sources, including impact of agriculture, and urban sources such as urban runoff and combined sewer overflow. Cadmium, copper and lead were identified as metals of concern both in the water, using log-normal statistics of the data and in the sediment by the sediment-pore water concentration partitioning. Urban runoff was found to be the most significant source of contamination.

The North Avenue Dam represents a typical example of urban impoundments which have now reached the end of their usefulness.