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Water Quality Improvements Using Modified Sediment Control Systems on Construction Sites

McLaughlin, R.A., Hayes, S.A., Clinton, D.L., McCaleb, M.S., Jennings, G.D.
Transactions of the ASABE 2009 v.52 no.6 pp. 1859-1867
construction industry, runoff, sediment yield, water erosion, erosion control, water quality, total suspended solids, dams (hydrology), polyacrylamide, turbidity, North Carolina
A study of the water quality of discharges from three different sediment control systems was conducted on a large construction site in North Carolina. Samples were obtained during storm events at the outlets of 11 of these systems using automatic samplers. Turbidity and total suspended solids (TSS) were measured, and a storm-weighted average (SWA) was determined for the systems. Water discharged from five standard sediment traps with rock dam outlets and unlined diversion ditches with rock check dams had an SWA turbidity of 4,320 nephelometric turbidity units (NTU) and an SWA peak of 12,640 NTU over a total of 26 storm events. The representative TSS values were 4,130 and 11,800 mg L -1 , respectively. Measurements of runoff entering and exiting the traps suggested that heavy sediment was being captured, but turbidity was not reduced. Three traps with modifications including forebays, porous baffles, improved ditch stabilization (lining, additional check dams), and polyacrylamide application had SWA and peak turbidity of 990 and 1,580 NTU, respectively, over a total of 31 events. Total suspended solids were also much lower, at 740 and 1,810 mg L -1 , respectively. Three basins with these same modifications, but with surface outlets, had somewhat higher average SWA values (1,560 NTU, 820 mg L -1), suggesting that the outlet type may not improve discharge water quality above the benefits of the other modifications to the standard sediment trap. However, when one of the latter systems was at optimal function, turbidity was reduced to below the receiving stream water levels (<100 NTU). These results strongly suggest that relatively simple modifications of commonly employed sediment trapping systems can dramatically improve discharge water quality and reduce the impacts on receiving waters.