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

Technical RequirementsSand FilterSand filter in parking lot, City of Sacramento Dept. of UtilitiesDescriptionA sand filter is a two-stage constructed treatmentsystem including a pretreatment sedimentationbasin and a filtration basin containing sand 1 . Thefilter bed is supported by a gravel base whichincludes an underdrain. As stormwater flows intoand through the system, large particles settle out inthe first basin and finer particles and other pollutantsare removed in the second basin. Runoff from largestorm events in excess of the water quality designvolume (WQV) are bypassed around the system.There are several variations of sand filters; this factsheet discusses the Austin Sand Filter.Siting Considerations• Tributary drainage area: Up to 50 acres.• Sizing basis: Water quality volume (WQV) with 48-hourdrawdown. Storm volumes in excess of the WQV must bebypassed.• Hydraulic head: about four feet of hydraulic head is required toachieve design flow through the Austin Sand Filter.• Total filtration basin depth (minimum): 36 inches.Vector Considerations• Potential for mosquitoes due to standing water will be greatlyreduced or eliminated if the sand filter is properly designed,constructed, and maintained.Advantages• Provides effective water quality enhancement through settlingand filtering while requiring relatively small space.• Can be placed above or below ground.• Does not require irrigation or base flow.• Suited for most soil conditions; permeable soils are not needed.• Reduces peak flows during small storm events.POLLUTANT REMOVALEFFECTIVENESSSedimentNutrientsTrashMetals*Bacteria*Oil andGreaseOrganics*HighLowHighHighMediumHighLimitations• Upstream treatment controls may be needed to pretreat and remove sediment from runoff beforeit enters the sand filter. This will prevent or minimize clogging.• Significant head loss through treatment units may limit use on flat sites.• More expensive to construct than other types of treatment control measures.General Maintenance Recommendations (Moderate to High)• Periodically remove debris and sediment from sedimentation basin and surface of filtration basin.• Periodically replace sand layer in filtration basin when filtration capacity is diminished.High*The following are target pollutantsfor Sacramento area: copper; lead;mercury; pathogens; dia zinon; andchlorpyrifosSource: CASQA CaliforniaStormwater BMP Handbook, January20031 Other absorptive filtering media, such as peat, may be used, but this fact sheet focuses on sand.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007SF-1