Seven construction sites in northwestern South Carolina were monitored during spring, summer and autumn of 2008 to quantify E. coli densities and evaluate their distribution and movement through sediment basin systems.Dry and wet-weather samples were collected from basin inlets, outlets, water column and deposited sediments. Although variable, Escherichia coli (E. coli) concentrations from construction site runoff (mean = 771 MPN/100 ml) were consistently and significantly higher than water quality criteria established by the US Environmental Protection Agency for recreational waters. While sediment basins are not recreational waters, they are likely to drain into such waters. Basin discharges showed significantly higher bacterial concentrations (mean = 1,368 MPN/ 100 ml) than flows coming directly from construction sites. Within sediment basins, both mean water column (877 MPN/100 ml) and mean sediment (188,828 MPN/100 ml) E. coli densities were higher than recommended EPA criteria, with mean concentrations in sediments, significantly exceeding corresponding overlying water column.The combined data suggest these sediment control practices are not acting to reduce bacterial concentrations, but rather the ponds appear to serve as reservoirs for viable E. coli and become net sources of bacterial loading to downstream receiving waters. Basin data were also analyzed using Pearson correlation between E. coli densities, total suspended solids (TSS) and rainfall depth. Across sites and sample locations, E. coli displayed a weak but significant correlation with TSS and with rainfall. Among sample locations and across dates, significant correlations were found between E. coli concentrations and TSS, pH, temperature and rainfall depth. Conclusions include: (i) E. coli are present at significant concentrations in construction-derived sediments; (ii) rainfall depth appears to significantly influence E. coli densities within these man-made hydrologic systems; (iii) construction site sediment basins in the Piedmont of South Carolina are serving as reservoirs of viable E. coli; and (iv) resuspension of subsequent transport of bottom sediments during storm events help account for the persistently elevated E. coli levels in sediment basin discharge.
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