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B. INFILTRATION Inflow <br /> Water Surface Elevatlor <br /> Inflfration systems Intercept and reduce direct site a: s; Aerobic c Zone <br /> surface runoff, allowing water to percolate back ,� <br /> Into the ground through coarse gravel, sand or d _ ; -- Standpipe Outlet <br /> other filtering media.These types of systems con- <br /> trol peak rates, help preserve existing on-site hy- 4'-0" •�� <br /> Perforated Pipe Inlet <br /> drology,maintain sfream base flow,and recharge Muck Layer <br /> yer <br /> Impermeable Llner <br /> Trenches- Trenches are shallow (two to 10 feet Figure VI-1:Gravel Trench <br /> deep)and are placed in relatively permeable soils Source:Cloytor <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 gablon,stone,sand, Street <br /> or a grassed covered area with a surface Inlet. <br /> Trenches allow for partial or total Infiltration of !P:�L..... . ,�' !' Metal Grate <br /> stormwater runoff Into the underlying soil. �(_ _ J:! 1 <br /> 1 3'-0"Deep Trench <br /> Basins-Basins are depressions created by exca- _ , <br /> •5"-2.s"Did. Clean Stone <br /> vation, berms, or small dams for the short term Tr <br /> ponding of surface runoff until It percolates Into <br /> —Protective Layer Filter Fabric <br /> the soil. i <br /> `*110 �.r;.,''j,i :__.• Filter Fabric Lined Sides <br /> Pervious Paving Systems- Pervious paving sys- ,, ~� i 6 12'Deep Sand Filter or Filter Fabric <br /> tems consist of strong structural materials,such as <br /> concrete or asphalt,regularly Interspersed with volds 'ri°ft y 'ill! 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 /> l'-2" Bedding Sand <br /> Roof Downspout Systems- Roof downspout sys- „- _ � � ---Compacted Aggregate <br /> terns consist of small-scale chambers or variations ___. .__, <br /> of infiltration trenches that are specifically designed Compacted Subgrade <br /> :.. <br /> to accept and Infiltrate roof drainage only. They 11�4 ,r` ;�- Y <br /> should be covered with rip rap to dissipate the — �._.. <br /> water's erosive energy. <br /> Figure Vi-3:Pervlous Paving <br /> Hedrt of <br /> Stormwater Design Guidelines VI -2 <br />