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<br />. <br /> <br />e <br /> <br />Engineer of Record shall adjust the depth of the proposed pipe accordingly. The <br />City of La Porte reserves the right to require greater depth where the need is <br />perceived by the City. <br />3. Sanitary sewers laid in street rights-of-way with crowned roads and roadside <br />ditches shall have a minimum depth of 6 feet from the crown of the road to the <br />top of the pipe and an absolute minimum cover of2 feet below the flowline ofa <br />roadside ditch when non-rigid or pipes of low hoop strength are used. The City <br />of La Porte shall have final determination on any deviation from these criteria. <br />4. Where the cover over the pipe is less than 2 feet, the sanitary sewer shall be laid <br />with Class 150 pressure pipe, steel pipe or ductile iron pipe. Class 150 pressure <br />pipe must be laid with cement stabilized sand backfill in accordance with the <br />Standard Details. Ductile iron pipe maybe used but shall be lined with either a <br />polyethylene or polyurethane coating with manufacturer recommendation and <br />applied by the pipe manufacturer. The minimum liner thickness shall be 40 mil. <br />Other rigid pipe or pressure pipe will be considered for approval on a case-by- <br />case basis by the City Engineer. <br />5. Maximum depth for 8-12 inch diameter collection lines shall be 20 feet from <br />average ground surface to sanitary sewer invert. Depths greater than 20 feet <br />shall require the use of Class 150 pressure pipe with cement stabilized sand <br />backfill in accordance with the Standard Details. Ductile iron pipe may be used <br />but shall be lined with either a polyethylene or polyurethane coating with <br />manufacturer recommendation and applied by the pipe manufacturer. The <br />minimum liner thickness shall be 40 mil. <br /> <br />I. Line Grades <br /> <br />1. The following table lists the minimum grade for 6-inch to 39-inch diameter <br />public sanitary sewers. The recommended velocity for a sanitary sewer flowing <br />full shall be 2.0 feet per second (fps). The maximum recommended grade shall <br />be calculated by the Professional Engineer of Record for a maximum velocity of <br />4.5 fps based on a Manning equation for full flow with the Manning's "n" equal <br />to 0.013. <br /> <br />Table 4.1 <br />MINIMUM GRADES FOR SANITARY SEWERS <br /> <br />PIPE SIZE MINIMUM GRADE (PERCENn <br />6 0.50 <br />8 0.33 <br />10 0.25 <br />12 0.20 <br />15 0.15 <br />18 0.11 <br />21 0.09 <br />24 0.08 <br />27 0.06 <br />30 0.055 <br />33 0.05 <br />36 0.045 <br />39 0.04 <br /> <br />Sanitary Sewer Design Criteria Page 8 of 11 <br />