TWO YEAR OF BIOCELL PERFORMANCE IN EASTERN IOWA: FIELD AND LABORATORY EXPERIMENTS

Storm water management is an increasing concern for Midwestern cities in the face of suburban expansion and climate shifts toward more intense rainfall events. Bioretention cells (biocells) are a best management practice that can used to mitigate the impacts of urban storm water runoff, in much the same way as standard detention basins do, but with added ecological and potential water quality benefits. Although biocells are increasingly being used for storm water management by municipalities and industry, quantitative data on how they perform through time and in varied physical environments is generally absent. We have monitored the performance of one biocell in Iowa City for two years and have completed laboratory freeze-thaw and percolation experiments on three commonly used biosoil mixes. Combined, the studies indicate that manufactured soil mixtures with significantly less sand content than is typically recommended provide infiltration rates that exceed design standards. The study also provides quantitative data that could be used to revise design standards for biocells, so that infiltration rates are considered in determining the amount of freeboard required to contain design storms. This could reduce the cost of biocell construction and make them an economically more attractive best management practice.