Author(s): Calvin Sawyer; William Ish; John Hayes; William Bridges; Louwanda Jolley; Christopher Post
Linked Author(s):
Keywords: Escherichia coli; Water quality criteria; Construction site runoff; Nonpoint source pollution; Sediment detention basin; Bacteri
Abstract: Large construction sites can have significant temporary and permanent impacts on the physical landscape. Excess sediment is frequently deposited into nearby surface waters, altering benthic habitat, reducing water clarity and transporting other pollutants such as enteric bacteria. To capture eroded soil and attenuate storm discharge peaks, many permitted construction projects larger than 10 acres in South Carolina require the installation of a sediment detention basin. Sediment-laden runoff is routed to a newly excavated impoundment, where larger particles settle out of suspension. Thus an entirely new hydrologic feature designed to concentrate eroded sediment and water is introduced into the landscape. Eight construction projects and their associated sediment basins were monitored in Anderson, SC during the spring, summer and autumn of 2008 to evaluate Escherichia coli (E. coli) densities and assess relationships with observed environmental variables. Dry and wet-weather samples were collected from basin inlets, outlets, water column and deposited sediments. Bacterial concentrations from construction site runoff measured at inlets (mean=771 MPN/100 ml) were consistently and significantly higher than water quality criteria established for primary contact recreation by the US Environmental Protection Agency. Basin discharge measured at outlets showed significantly higher bacterial concentrations (mean=1368 MPN/100 ml; t-stat=3.54; p=. 0036) than those found in construction site runoff and also exceeded EPA standards. Within sediment basins, both mean water column (877 MPN/100 ml) and mean sediment (1.8E+5 MPN/100 ml) E. coli densities were higher than recommended EPA criteria, with mean concentrations in the sediments significantly exceeding the corresponding overlying water column (t-stat=5.51; p<. 0001). Aggregated data suggest these sediment control practices are not acting to reduce bacterial concentrations, but rather appear to be serving as reservoirs for viable E. coli and net sources of bacterial loading to receiving waters. Quantification of construction site bacterial runoff, potential basin-related bacterial contamination, and examination of site discharges will assist stormwater regulators and engineers in evaluating the efficacy of state construction permit standards and confirm whether site design practices are protective enough of receiving water quality. Results may also provide information to assess whether the present course of construction-related stormwater design and management is suitable or sustainable.
Year: 2010