Modeling the Performance of Sand Filters for Removing Runoff Suspended Sediment

Geotextile tubes filled with sand are being evaluated for filter treatment of runoff containing lead and other metals stemming from firing small arms on military training ranges. Such filter tubes trap total suspended sediment (TSS) in the runoff, thus removing most of the metals, which are adsorbed to the sediment. Mathematical models were developed within two Excel workbooks to assess sand filter performance for a cascade of filters capturing runoff from the impact area of small arms firing ranges. One of the workbooks assesses filter cascade characteristics for a single design storm, while the other workbook assesses filter characteristics for a continuous, steady rainfall so that the useful life of the filters, as impacted by clogging, could be estimated. Model computations include the approach depth of flow, including filter over-topping, and the flow rate through each filter over time for specific storm events. The time history of effluent TSS concentration and the TSS trapped within each filter are also computed, as well as the TSS removal coefficient and hydraulic conductivity of each filter. The models provide useful general performance information. In order to provide more specific performance information, laboratory experiments with site-specific sand filter material and runoff TSS are required to determine three filter parameters that can be used as part of the model input. The original document contains color images.