Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Technical RequirementsSand FilterHow does a sand filter work?A typical configuration of an Austin Sand Filter is shown in Figure SF-1. The principal components ofthe unit include a sedimentation basin and a filtration basin. The sedimentation basin is designed to holdthe entire WQV and to release that volume to the filtration basin over the design drawdown time of 40hours. Large sediment is removed from the runoff through this process. Fine particles and other pollutantsare removed in the filtration basin as the runoff passes through the sand filter. Runoff in excess of theWQV is bypassed around the treatment unit.Variations of Sand FiltersThis fact sheet focuses on the Austin Sand Filter. Other variations (also named after the area of thecountry where they were developed) include the underground (DC) sand filter and the linear or perimeter(Delaware) sand filter. The size of the drainage area and the facility location typically dictate what type offilter is best. For large watersheds (i.e., up to 50 acres), an Austin Sand Filter is recommended. For smallcatchments up to 1.5 acres requiring underground facilities, a DC Underground Sand Filter isrecommended. Delaware Linear Sand Filters are especially suitable for paved sites and industrial sites(catchments up to five acres in size) because they can be situated to accept sheet flow from adjacentpavement. The units also differ in hydraulic head requirements. Approximately four feet of hydraulichead is required to achieve design flow through the Austin and DC Underground Sand Filters, whereasDelaware Linear Sand Filters can operate with as little as two feet of head.Planning and Siting Considerations• Sand filters are generally suited for sites where there is no base flow and the influent sedimentload is relatively low.• Sand filters are well suited for drier areas and/or urban areas because they do not requirevegetation or irrigation and require less space than most other treatment controls.• Because the filter media is imported sand or engineered adsorptive material, sand filters are suitedfor most soil conditions, and the presence of permeable soils is not a requirement.• The Austin Sand Filter may be constructed inside a concrete shell, or built directly into the terrainover an impermeable liner (e.g., clay), if site conditions allow. Figure SF-1 shows a unit within aconcrete shell, with an enclosed sedimentation basin and the filtration basin open at the surface.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsSF-2 May 2007