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3.1.3 Perforated Stub-Out Connections <br /> A perforated stub-out connection is a length of perforated pipe within a <br /> gravel-filled trench that is placed between roof downspouts and a <br /> stub-out to the local drainage system. Figure 3.8 illustrates a perforated <br /> stub-out connection. These systems are intended to provide some <br /> infiltration during drier months. During the wet winter months,they <br /> may provide little or no flow control. Perforated stub-outs are not <br /> appropriate when seasonal water table is< 1 foot below trench bottom. <br /> In single-family subdivision projects subject to Minimum Requirement#7 <br /> for flow control(see Volume I),perforated stub-out connections may be <br /> used only when downspout infiltration or dispersion is not feasible per the <br /> criteria in Sections 3.1.1 and 3.1.2. <br /> Location of the connection should be selected to allow a maximum <br /> amount of runoff to infiltrate into the ground(ideally a dry location on the <br /> site that is relatively well drained). To facilitate maintenance,the <br /> perforated pipe portion of the system should not be located under <br /> impervious or heavily compacted(e.g.,driveways and parking areas) <br /> surfaces. <br /> Perforated stub-out connections should consist of at least 10 feet of <br /> perforated pipe per 5,000 square feet of roof area laid in a level,2-foot <br /> wide trench backfilled with washed drain rock. The drain rock should <br /> extend to a depth of at least 8 inches below the bottom of the pipe and <br /> should cover the pipe. The pipe should be laid level and the rock trench <br /> covered with filter fabric and 6 inches of fill (see Figure 3.8). <br /> Setbacks are the same as for infiltration trenches. <br /> Potential runoff discharge towards a landslide hazard area must be <br /> evaluated by a professional engineer with geotechnical expertise or a <br /> licensed geologist, hydrogeologist, or engineering geologist. The <br /> perforated portion of the pipe may not be placed on or above slopes <br /> greater than 20%or above erosion hazard areas without evaluation by a <br /> professional engineer with geotechnical expertise or qualified geologist <br /> and jurisdiction approval. <br /> For sites with septic systems,the perforated portion of the pipe must be <br /> downgradient of the drainfield primary and reserve areas. This <br /> requirement can be waived if site topography will clearly prohibit flows <br /> from intersecting the drainfield or where site conditions(soil permeability, <br /> distance between systems, etc) indicate that this is unnecessary. <br /> February 2005 Volume !ll—Hydrologic Analysis and Flow Control BMPs 3-17 <br />