Evaluation of Regionally Appropriate and Cost Effective Bioretention Media Mixes

Bioretention basins have the potential to reduce the volume and velocity of stormwater flows and remove some stormwater contaminants. However, because they are a function of soil or sand-based media mixes, their design may vary by geographical region. Laboratory soil column experiments were conducted to determine the mix media and proportions that would likely perform well in field-scale basins in the Charlotte-Mecklenburg region of North Carolina. Specifically, the study focused on the contaminant removal capacity of native piedmont soils (red clay, yellow clay, and top soil, compost, and sand) in media mixes. Further feasibility of substituting some inexpensive waste materials (crushed brick, ground glass, and tire chips) for sand and gravel was assessed with respect to contaminant removal. The results showed clay soils that typify the Piedmont region are fair performers with respect to pollutant removal; however, infiltration rates were slow and could lead to potential long-term operation and maintenance problems. Commercial topsoil performed best when amended with sand. Lower nutrient removal was noted in columns containing compost. Overall, the alternative materials performed comparably to control columns containing standard construction sand and gravel.