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

Technical RequirementsSand FilterDesign CriteriaDesign criteria for the Austin Sand Filter are listed in Table SF-1. Use the Design Data Summary Sheetprovided at the end of this fact sheet (Table SF-3) to record design information for the permittingagency’s review.Table SF-1. Austin Sand Filter Design CriteriaDesign Parameter Criteria NotesSedimentation BasinMaximum tributary drainage area 50 acres The larger the tributary area, the larger the surface areaof filter required.Minimum basin volume WQV See Appendix E in this Design ManualMinimum/Maximum basin water depth (d SB ) 3ft/10 ftMinimum length/width ratio 2:1Maximum drawdown time 48 hrs Based on WQV (See Appendix E)Freeboard 1 ft Above maximum water surface elevationMaximum inlet velocity 3 ft/sec Provide inlet energy dissipater as required to limit inletvelocity to 3 ft/secFiltration BasinMinimum gravel depth over sand filter (ifapplicable)2 in. See Figures SF-3 and 4Minimum storage volume above filter bed 20% Based on WQVMinimum storage depth above filter bed (d s )3 ftMinimum sand depth in filter bed (d f ) 18 in. Place geotextile fabric between sand and gravel layersCoefficient of permeability for sand filter (k) 3.5 ft/day 0.146 ft/hourSand size, diameter0.02-0.04 in.Slope of sand filter surface 0% flatMinimum gravel cover over underdrain 2 in. Gravel not required under the drain pipeUnderdrain gravel size, diameter0.5-2 in.Minimum inside diameter of underdrain6 in.Underdrain pipe type PVC Schedule 40 (or heavier)Minimum slope of underdrain 1%Minimum underdrain perforation, diameter 0.375 in. 3/8 inchMinimum perforations per row 6Minimum space between perforation rows6 in.Maximum drawdown time (t f )48 hrsMinimum gravel bed depth, (d g )16 in.Liner (if required)ClayStormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007SF-3