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B. INFILTRATION Inflow <br /> Water Surface Elevatior <br /> Infiltration systems Intercept and reduce direct site a:, f. cr Anaerobic Zone <br /> surface runoff, allowing water to percolate back ,,� Aerobic Zone <br /> Into the ground through coarse gravel, sand or 4 _ ; -- Standpipe cutlet <br /> other filtering media.These types of systems con- <br /> trol peak rates, help preserve existing on-site hy- 4'-0" ' <br /> drok)gy,maintain stream base flow,and recharge Perforated Pipe Inlet <br /> groundwater, –�`Muck Layer <br /> Impermeable Liner <br /> Trenches- Trenches are shallow (two to 10 feet F! ure VI-1:Gravel Trench <br /> deep)and are placed In relatively permeable soils Source:Claytor <br /> that are backfilled with coarse stone,a sand filter, <br /> and lined with filter fabric.The trench surface can <br /> be covered and/or consist of gabion,stone,sand, Street <br /> or a grassed covered area with a surface Inlet. <br /> Trenches allow for partial or total Infiltration of '>~1..... . y Metal Grate <br /> stormwater runoff Into the underlying soil, �j_^__ i �'��� <br /> 3'-0"Deep Trench <br /> Basins-Basins are depressions created by exca- 1,5"-2.5"Dla, Clean Stone <br /> vation, berms, or small dams for the short term - - <br /> ponding of surface runoff until it percolates Into <br /> Protective Layer Filter Fabric <br /> the soil. �i"- - <br /> ' ':; jiL:.X. Filter Fabric Lined Sides <br /> Pervious Paving Systems- Pervious paving sys- <br /> tems consist of strop structural materials, * – -f- <br /> 6' <br /> -12'Deep Sand Filter or Filter Fabric <br /> gsuch as ��---.=�..�:.__::_:.. . <br /> concrete or asphalt,regularly Interspersed with voids Subsoil <br /> which are filled with pervious materials such as <br /> sandy loam or grassed turf.These surfaces are un- <br /> derlain by soils capable of allowing infiltration.Per- <br /> vious asphalt is not recommended for clay-rich <br /> soils since it easily clogs and thus necessitates fre- <br /> quent replacement. Pavers with Sand Filled Joints <br /> 1%2" Bedding Sand <br /> Roof Downspout Systems- Roof downspout sys- Compacted Aggregate <br /> tems consist of small-scale chambers or variations __ — ---- Z7 -r – Geotextlle <br /> of infiltration trenches that are specifically designed `v::;: <br /> p� y _ ....- - – - _Compacted Subgrade <br /> lo <br /> to accept and Infiltrate roof drainage only. They <br /> should be covered with rip rap to dissipate the -=P«! IIT <br /> water's erosive energy. <br /> Figure Vi-3:Pervlous Paving <br />