Postaudit of Upper Mississippi River BOD/DO model

In 1981 the Minnesota Pollution Control Agency completed a wasteload allocation study of the Metropolitan Wastewater Treatment Plant's [11 m3/s (250 mgd)] impact on dissolved oxygen levels in Pool 2 of the Upper Mississippi River, using the water quality model AESOP. Subsequently, a low flow water quality survey was conducted in the summer of 1988 to monitor the improvement in the river following the treatment upgrade at the plant. In this postaudit study, the AESOP model was checked using the 1988 data set. The significance of the postaudit analysis is that the model kinetic coefficients remain unchanged, except the biochemical oxygen demand deoxygenation rate and the algal growth rate, from the 1981 wasteload allocation study. The carbonaceous biochemical oxygen demand (CBOD) deoxygenation rate dropped after treatment upgrade, and the algal growth rate is within the range of values used in previous calibrations of the AESOP model. CBOD and ammonia loads from the Metro Plant now contribute a small dissolved-oxygen deficit in the receiving water.