Stormwater carries contaminants that pollute ground and surface waters. Decentralized treatment of stormwater using best management practices (BMPs) is the commonly accepted practice for mitigating contamination downstream. Bioretention basins provide treatment by slowing the flow of stormwater and via soil and plant associated processes. Michigan State University finished construction of a large scale bioretention basin in spring 2010. During construction numerous challenges arose which resulted in the as-built site differing from the original engineering design. Monitoring of chemical oxygen demand (COD), pH and total solids (TS) at the Farm Lane Bioretention Research Facility began in spring 2011 and is ongoing. It was concluded that little to no treatment is taking place within the bioretention basin. Numerous attempts to improve the water flow through the system have been completed, but have yielded few results. An additional study was completed evaluating the stormwater treatment performance of three plant species - Iris virginica, a Carex mix and fescue grass - in the five cells within the basin. An aerator was installed in the pond directly preceding the research cells to determine the impact of aeration on the water quality. Total nitrogen, total phosphorus, COD, pH and TS were evaluated at the influent and effluent locations. Congruent with overall monitoring of the site little to no treatment was observed in the five cells regardless of aeration. The bioretention basin is likely affected by contaminated materials used during construction. The Farm Lane bioretention basin provides an example of the importance of monitoring construction, as post construction changes are costly and challenging.
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