Design, Construction and Lessons Learned from Oklahoma Bioretention Cell Demonstration Project

Ten bioretention cells were constructed in Oklahoma to demonstrate the effectiveness of the technology for stormwater runoff volume reduction and phosphorus attenuation. The cells embraced a variety of land uses including residential, public, and commercial and ranged in volume from 19 to 435 m³. Designs featured sand plugs in the top soil layer for improved infiltration, and 1:1 side slopes for safety during construction. A blend of sand and 5% fly ash was used as the filter layer medium to enhance phosphorus attenuation. Of the ten cells, eight were installed by a contractor selected through a formal state bidding process during Summer 2007. The remaining two were constructed primarily by Oklahoma State University students and staff in Spring 2008. This article explores engineering considerations, general design procedures, site parameters, construction details, planting success and costs. Problems and successes encountered during the construction process are described and a comparison of contracted and in-house construction is presented.