Transport and Fate of Escherichia coli in Sediment Layer and Water Column of Basins on Active Construction Sites

Abstract

<abstract> <bold><sc>Abstract.</sc></bold> The conventional method of controlling sediment-laden runoff on construction sites is the use of sediment basins. These basins slow the velocity of runoff and allow particles to settle from the water column before discharge to surface waters offsite. However, the sediment layers that accumulate in these best management practices may create a reservoir for potentially pathogenic bacteria. Deposited sediment is known to provide protection for bacteria; therefore, while these basins decrease sediment loadings to water bodies downstream, they may introduce harmful levels of pathogenic bacteria into these surface waters when resuspended during rain events. In addition to causing human health risks, these high bacteria levels alter the natural biological makeup of downstream ecosystems. This article describes the fate and transport of Escherichia coli in construction site sediment basins. Three sediment basins, located in Anderson, South Carolina, were sampled after rain events to explore trends in E. coli densities that exist among various sediment depths as well as inflow and outflow of basins. Results provide evidence to suggest that sediment basins are a reservoir for indicator bacteria. Data show that E. coli was most concentrated in the top layer of sediment, and high densities persisted for five to ten days. In addition, E. coli densities were higher in outflow than inflow. Consequently, high densities of bacteria may be routed to downstream waters. This research provides considerable evidence that the sediment layer in man-made construction basins can cause detrimental effects to surface waters. With this knowledge, better stormwater management practices may be developed with the goal of remediating impaired surface waters.