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<br />CHAPTER 5: INFILTRATION TRENCHES <br /> <br />Infiltration trenches are an adaptable BMP that effectively remove both <br />soluble and particulate pollutants. As with other infiltration systems, <br />trenches are not intended to trap coarse sediments. Grass buffers (for <br />surface trenches) or special inlets (for underground trenches) MUSt be <br />installed to capture sediment before it enters the trench. Depending on the <br />degree of storage/exfiltration achieved, trenches can provide groundwater <br />recharge, low flow augmentation and localized streambank erosion control. <br />Individual trenches are primarily an on-site control, and are seldom <br />practical or economical on sites larger than 5 or 10 acres. Trenches are <br />only feasible when soils are permeable and the water table and bedrock are <br />situated well below the bottom of the trench. Aside from regular inspections <br />and more rigorous sediment and erosion control, trenches have limited routine <br />maintenance requirements. However) trenches will prematurely clog if <br />sediment is not kept out before, during and after construction of a site.' If <br />a trench does become severely clogged, partial or complete replacement of the <br />structure may be required. <br /> <br />Figure 5.1: Schematic of an Infiltration Trench <br /> <br />Wellcap <br />" <br /> <br />Observation Well <br /> <br /> <br />Sand Filter (6-12 Feet Oeep) <br />or Fabric Equivalent <br /> <br />'" <br />Aunofl ExRltrates <br />. Through Undlslurbed Subsoils <br />with a Minimum fc ot 0.5 Inches/Hour <br /> <br />I <br /> <br />-: <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />.. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br />.. <br /> <br />I <br />