United States Department of Transportation
i
Erosion, Sediment, and Turbidity Control and Monitoring Research to Meet Water Quality Goals
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2017-01-01
[PDF-5.04 MB]
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Edition:Final report, 08/16/2013 – 06/30/2017
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Abstract:Quality Goals Construction sites usually create large areas of exposed soil which can produce runoff containing high sediment concentrations and turbidity. While standard practices can improve water quality, the use of surface outlets and chemical treatment can further reduce the discharged water turbidity by an order of magnitude or more. This project explored a variety of approaches to both measuring water quality and improving it, as well as the potential impacts to freshwater mussels from of construction site runoff. Four different surface skimmer outlet devices were tested under controlled, full-scale conditions to determine discharge rates as affected by orifice size and water depth. Water quality determination by up to three different sampling methods and two recording meters were also compared for turbidity values. A portable rainfall simulator capable of producing 2-3” hr-1 rainfall over a large (10’ x 20’) area was constructed for erosion testing. Two different dissolved flocculant dosers were constructed to have dosing controlled by either rainfall or runoff flow rates, and these were tested on three construction projects. Finally, a range of polyacrylamides (PAM) with different properties were tested for toxicity to three freshwater mussel species. Further testing of the toxicity of settled sediment, PAM-flocculated sediment, and suspended sediment was performed over two time periods for juvenile mussels. Three of the four skimmers had relatively linear discharges as water levels dropped from 5’ to 1’ in the test basin, with a fourth having steadily declining discharge rates. The discharge rates determined in this study were often different than those provided by the manufacturer, but test conditions were not necessarily the same. Turbidity determination by sampling or by recording probe often produced different values but usually similar trends, and the two recording probes provided similar values. The rainfall simulator produced droplets similar to those reported for other simulators and the rainfall distribution was highly influenced by wind speed, since no shielding was used. However, 2-3” h -1 occurred in most of the plot area. The two different dissolved flocculant dosers had success in reducing turbidity primarily during moderate events, but during high-flow and –sediment events there was turbidity reduction but turbidity remained high. These would have to be scaled up to treat those events. The mussels appeared to tolerate the PAM at concentrations >10X the targeted treatment level, and suspended sediment stressed the juvenile mussels more than settled or PAM-flocculated sediment. This suggests reducing turbidity with PAM would also reduce impacts on mussels in receiving waters.
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