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

Technical RequirementsInfiltration BasinDescriptionAn infiltration basin is a shallow earthen basinconstructed in naturally pervious soils (usuallyType A or B) and designed for infiltratingstormwater. An infiltration basin functions byretaining runoff and allowing it to percolate into theunderlying native soils and into the groundwatertable over a specified drawdown period. Thebottoms and side slopes of infiltration basins aretypically vegetated with dryland grasses or irrigatedturf grass.Photo credit: Wisconsin DNRSiting Considerations• Tributary drainage area: Up to 50 acres.• Soil Infiltration Rate: 0.5-2.0 in/hr (permeability test required).Soils with higher infiltration rates require pretreatment device.• Depth to groundwater: ≥10 ft from basin bottom.• Existing groundwater contamination.• Setback requirements: 100 ft from wells; 20 ft downslope and 100ft upslope from foundations.• Topography: Not appropriate on fill or steep slopes.Vector Considerations• Potential for mosquitoes due to standing water will be greatlyreduced or eliminated if the basin is properly designed,constructed, and operated to maintain its infiltration capacity anddrawdown time.POLLUTANT REMOVALEFFECTIVENESSSedimentNutrientsTrashMetals*Bacteria*Oil and GreaseOrganics*HighHighHighHighHighHighHigh*The following are target pollutants forSacramento area: copper; lead; mercury;pathogens; diazinon; and chlorpyrifosSource: CASQA California StormwaterBMP Handbook, January 2003Advantages• Reduces or eliminates stormwater discharge to surface waters during most storm events• Reduces peak flows during small storm events.• Can be incorporated into site landscape features or multi-use facilities such as parks or athleticfields.Limitations• Not appropriate for areas with slowly permeable soils, high groundwater or existing groundwatercontamination.• Not appropriate for industrial sites or locations where spills may occur.• Must be protected from high sediment loads. Once clogged with sediment, restoration of basininfiltration capacity may be difficult.General Maintenance Recommendations (Low to Moderate)• Maintain vegetation as in any landscaped area.• Periodically remove debris and sediment from basin floor.• Repair/replace vegetation as necessary to maintain desired cover.• Check and record drawdown time during and after major storm events to document infiltrationrates.• Remove sediment and/or scarify basin bottom to restore infiltration capacity when maximumdrawdown time for WQV is exceeded.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007IB-1