Influence of Planting Soil Mix Characteristics on Bioretention Cell Design and Performance

Municipalities are increasingly interested in using rain gardens, or bioretention cells, as a "best management practice" (BMP) for storm-water management and as a component of low impact development. However, improved technical reference materials are needed to determine the influence of planting soil mix design on the hydrologic and water quality performance of bioretention cells. This article describes three investigations undertaken to determine the influence of planting soil mix characteristics. The first was to identify the bioretention cell design characteristics and methodologies used by different agencies. The second was a laboratory investigation on the soil characteristics that influence performance including field capacity, saturated hydraulic conductivity, soil moisture content, organic content, dry bulk density, porosity, and sediment grain size distribution. The third was to quantify the effectiveness of bioretention cells as a storm-water BMP by designing, constructing, and monitoring two full-scale bioretention cells on the campus of Lawrence Technological University in Southfield, Mich. Analysis included quantifying volume retention, peak discharge reduction, and removal of storm-water pollutants including total suspended solids, total phosphorus, and total nitrogen.