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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br /> 16. Matenals speci6cations for any permanent piped system are listed in the City's DCSS, and shall � <br /> be approved by thc City. <br /> Maintenance Standards <br /> I. Check inlct and outict points regularty,especially aftcr storms. <br /> 2. The inlet should bc free of undercutting,and no e�atcr s6ould be going around the point af entry. <br /> If there aze problcros,thc hcadwall should be reinforced with compacted catth or sand bags. <br /> 3. Thc oudet point should be free of erosion and installed wit6 appropriate oudet protection. <br /> 4. For pem�ancnt iastallations, inspect pipe periodically for vandalism and physical distress such as <br /> slides and wic�1-throw. <br /> 5. Nocmelly the pipe slope is so stcep thac c(ogging is not a problem with smooth wall pipe, <br /> however,debris may become lodged in the pipe. <br /> 3.3.6 BMP C205: Subsurface Drains <br /> Purpose <br /> To intercept, collect,and convey gtoundwater to a satisfactary outlet,using a perForated pipe or conduit <br /> below thc ground surCace. Subsudace drains arc also known as "Gcnch drains." The pedorated pipc <br /> provides a dewatering mechanism to dtain excessively wet soils,provide a stable base for canshuction, <br /> improve stability of shuciures with shallow foundations,or to rcducc hydrostatic pressurc to improve <br /> slopc stability. <br /> Conditions o/Use <br /> Usc when excessive watet must bc removed from the soil. Thc soil pertneability,depth to water table and � <br /> impervious layers are all factors which may govcm the use of subsurface drains. <br /> Relief drains arc used either to lower the water table in latge,relatively flat areas, improve the grawth of <br /> vcgetation, or to remove sudace water. They are installed along a slope and drain in the directian of the <br /> slope,and can be installcd in a grid pattem,a hecringbone panern,or a random pattcm. <br /> Ioterceptor drains arc used to rcmove excess groundwaler Gom a slopc,stabilize stcep slopes, and lowcr <br /> We water table immediatcly below a slopc to prevent thc soil Gom becoming saturated. They are installed <br /> perpendicular to a slope and drain to t6e side of the slope and usually consist of a single pipe or scries oC <br /> singlc pipes instead af a pattcrned layout , <br /> Design and lnstalfatJon Specificafions <br /> Depth und spacing af interceptor drains <br /> 1. The depth of an interceptor drain is detertnined primanly by thc depth to which thc watcr iable is <br /> ro be lowcred or the depth to a confining laycr. For pracrical rcasons,thc maximum depth is <br /> usually limited ro 6 fect,with a minimum covcr of 2 fcet to protect the conduit. <br /> 2. The soil should have depth and sufficient permcability to permit installation of an effective <br /> drainagc system at 3 dep[h of 2 to 6 fcet. <br /> 3. M adcquate oudet for thc drainage systcm must bc availa6le either by gravity or by pumpir.g. <br /> 4. The quantity and quality of discherge needs to be accounted far in lhe recciving strcam <br /> (additiona!deteotion may be requ'ved). <br /> 5. This standazd docs not apply lo subsurface drains for building foundations or dcep excavations. <br /> Volume 11—Construction Stormwater Pollution Pr�vention <br /> 3-43 <br />