12/19/2001 Env Bd Packet - Laserfiche WebLink

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b& 10 On -Lot Infiltration General Description On -lot infiltration systems promote infiltration at the individual lot level, controlling runoff at its source. These systems are off -line and generally receive sheet flow runoff. The main feature that distin- guishes these systems from other infiltration systems (such as infiltration basins and trenches) is scale. These small systems accept runoff from a single residential lot. Although infiltration basins and trenches have many design features in common with on -lot infiltra- tion systems, the Infiltration Basins and Infiltration Trenches BMP Sections refer to larger lot, end -of -pipe facilities. On -lot infiltration systems' primary function is to mitigate the normal impacts of urbanization on the natural water balance. This is done by turning water that would normally become surface runoff (a waste product) into a resource that waters trees, recharges groundwa- ter and provides stream baseflows. On -lot infiltration systems also function to improve water quality by removing some pollutants from the runoff as it infiltrates. Also, because these systems serve to reduce the volume of runoff, they contribute to both erosion protec- tion and flood control. Lastly, the use of these systems reduces the size and cost of downstream water control facilities. On -lot infiltration systems include: • Reduced lot grading (Figure 1) • Directing roof leaders to soakaway pits (Figures 2 through 4) • Directing roof leaders to rain barrels (Figure 6) • Directing roof leaders or other surface runoff to other vegetated areas, such as rainwater gardens (Figures 7 through 10) These source controls address measures that can be applied by the developer or the homeowner. Public education programs within municipalities can help to educate citizens on the role they can play in the application of these systems. On -lot infiltration systems are not to be used for infiltrating any Metropolitan Council / Barr Engineering Co. Purpose Flow attenuation Water Quantity 11 Runoff volume reduction Pollution Prevention Soil erosion Sediment control Nutrient loading Water Quality N/A N/A N/A Pollutant Removal (Soakaway Pits and Rainwater Gardens) Total suspended sediment (TSS) Total phosphorus (P) Nitrogen (N) Heavy metals Floatables Oil and grease Other Fecal coliform Biochemical oxygen demand (BOD) • • • • 11 • 11 11 • 11 Primary design benefit Secondary design benefit Little or no design benefit 3 -141