Designing an Effective SCS by Treating Sediment with Polymers

摘要

If a Sediment Containment System (SCS) is to be effective for capturing a design size particle by gravity, it must allow for the flow of water through the system and provide sufficient time for sediment deposition. Traditionally, attempts at this goal include specifying a capture volume of 252 cubic meters per hectare (3,600 cubic feet per acre) or capturing a design size particle (e.g., 0.02 mm in diameter) found in incoming runoff waters. Unfortunately, practicality usually results in development of a SCS that:1. Captures only large (e.g., medium silt and larger) diameter particles,2. Does not prevent colloidal size particles from discharging out of the system,3. Requires large containment systems to ensure sufficient settling times,4. Does not address discharges that are larger than design specifications, which results in additional sediment leaving the site, and5. Has a net effectiveness for capturing sediment that is often much less than 100%.This paper presents equations and graphs that demonstrate how SCS parameters change when treatment of sediments and inflow waters by a polymer happens. By incorporating the results from laboratory analyses of representative contributing soils samples into equations found in Fifield (2004), an evaluation of vertical terminal velocity and acceleration conditions occurs. Upon developing and applying the hew equations to various examples, it is possible to illustrate that when adding polymers to incoming runoff waters in a controlled manner, the net effectiveness for a SCS to remove sediment from runoff waters can approach 100%.Initial assessment indicate that pond surface areas may be up to 94% smaller with polymer treated sediments when compared to non-treated systems and may need only about one-fourth of the flow path distances. Finally, the equations also provide a method to assess how nephelometric turbidity units (NTUs) will vary for discharge waters when the design of an SCS structure is not adequate.