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

Runoff Reduction Fact SheetDisconnected Roof DrainsVariation/ParameterCriteriaDry Well onlySetbackCapacityMust be located a minimum of 20 feet from building. A smaller setback maybeallowed with geotechnical engineer approval.Must design a minimum 24 cubic feet of storage capacity for every 1750 squarefeet of contributing roof area.Drain RockPerforated Chamber (ifallowed)Surface LabelMust be filled with drain rock or use perforated chamber (with or without rock) uponapproval of permitting agency.Perforated chambers must be designed and installed according to manufacturersspecifications. Perforations in structure must allow for discharge of water at a ratehigher than soil infiltration rate. Must be lined with geotextile fabric. Consultmanufacturer’s specifications for additional design requirements.Surface identification label may be required; check with the local permitting agency.Source: High Point Community Site Drainage Technical Standards. Seattle, WATable DRD-3.Inspection and Maintenance Recommendations for Dispersal Trenches and Dry WellsDisconnected Roof Drains - GeneralGuttersOverflowDispersal Trench and Dry WellSurface and VegetationMaintenancePretreatment SumpPonding Water/MosquitoControlManufacturer’sRecommendations• When cleaning gutters, repair wire mesh as needed to keep leaves and debris out ofdrain pipes.• Periodically inspect and clear overflow pipe.• Keep the surface clean and free of leaves, weeds, debris, and sediment, and do notreplace or cover it with an impermeable paving surface.• Do not store loose material such as bark or sand over dry well or trench area; this canclog the infiltration facility.• Do not plant trees or shrubs over infiltration structures. Grass and plants (especiallydrought-tolerant varieties) are best.• Use integrated pesticide management techniques and minimize use of fertilizers,herbicides and insecticides in vegetated areas.• Remove grass clippings in grass areas over infiltration structures.• Reseed grasses when needed and keep healthy and dense enough to provide filteringwhile protecting underlying soils from erosion.• Inspect sump monthly and after heavy rainfall and clean out accumulatedsediment/debris as needed.• Check for and eliminate any ponding water that does not drain within 48 hours, sincethat provides an environment for insect larvae.• Standing water is usually an indication that the facility is clogged (the overflow and/orthe sump needs to be cleaned and/or the device needs to be reconstructed).• For manufactured products, follow manufacturer’s maintenance recommendations.• Make structural repairs when necessary to restore function.Replacement• Reconstruct or replace when it is no longer functioning properly. For planningpurposes, estimated life expectancies are as follows: dispersal trench - 30 years, drywell – 30 years. (Source: City of Portland, OR)Stormwater Quality Design Manual for the Sacramento and South Placer RegionsDRD-8 May 2007