MONTE CARLO MODELING OF WATER AND SEDIMENT CONTAMINATION BY TOXIC METALS AT THE NORTH AVENUE DAM, MILWAUKEE, WI, USA

A deterministic water - sediment quality model was developed with a Monte Carlo interface and input generation. The model was used to simulate water and sediment (total and dissolved-pore water) quality of a reach of Milwaukee River that includes an urban impoundment. The sediments in the impoundments are contaminated by toxic metals and other priority pollutants. The sediment - water quality model was composed of three sequential segments each represented by three systems: water, upper sediment and lower sediment layers. The mass balance of the sediment contaminants was strongly affected by the direction of the groundwater fluxes through the sediments. Steady state was assumed for the water column and the upper sediment layer while a dynamic mass balance model was used for the lower sediment layer. The inputs of the Monte Carlo simulation were ten years long time-series of upstream flows and Combined Sewer Overflow (CSO) discharges with corresponding Monte Carlo generated concentrations. The model calculated output concentrations which were statistically similar to the probability distribution of measured concentrations.