Qualitative Valuation of Performance Testing for Sediment Retention Devices (SRDs)

摘要

With the new U.S. Environmental Protection Agency (U.S. EPA) standards for construction effluent limits coming into effect by December 2009, the need for improved design approaches for erosion and sediment control is imperative. This also promotes the need for a greater understanding of the performance capabilities and limitations of sediment retention devices (SRDs). In order to improve on the design of SRD treatment train systems, how these controls attenuate eroded solids, the range of expected solids reductions, hydraulic capacities, and structural/functional limitations under various hydraulic loadings must be assessed through both reduced-scale and full-scale, controlled testing and field verification testing. Historically, there has been a lack of standardized testing protocols for assessing SRD. Only a handful of ASTM standards have been established for sediment controls, each having its own set of limitations. Among the existing protocols, ASTM D 5141 is a method designed to assess filter efficiency and hydraulic flux rates specifically for silt fence using site-specific soils. ASTM D 7351 is a protocol for assessing the solids removal efficiency of SRDs under inter-rill flow (sheet) flow conditions. ASTM D 5141 is a smaller, laboratory-scale setup, while the protocol for ASTM D 7351 requires a larger set up at the field level. ASTM D 7351 evaluates performance of the SRD based on percent soil retention and percent water retention. ASTM D 7208 is a standard protocol for assessing check dam performance in a concentrated flow (earthen ditch) application. However, the performance measures related to this protocol focus on quantification of earthen-channel erosion reduction (i.e., shear reduction) as compared to a control ditch containing no check dams. Protocols for SRDs should assess reductions in mass loadings of transportable solids, overall effluent quality, as well as hydraulic capacity and the effects on capacity under slurry-flow (elevated suspended-solids) conditions. Performance assessments should include effects on the hydraulic capacity of BMPs under clean-water flow and slurry-flow conditions. Assistance in determining what tests to perform for a given SRD and what to do with the results will be discussed.