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of the pipe existing the manhole shall not be higher than the lowest crown of the pipe <br />entering the manhole or 80 percent of the flow depth of the pipe exiting the manhole <br />shall not be higher than the lowest 80 percent flow depth of the pipes entering the <br />manhole. <br />A 0.1 -foot drop through the manhole shall be provided from upstream inlet and the <br />manhole outlet (2.9 percent slopes). For steep systems where pipe slopes are greater <br />than 3 percent the upstream pipe slope shall be carried through the manhole to the <br />outlet flow line elevation. A maximum drop of 24 inches is allowed through the <br />manhole. <br />2. Drop Manholes <br />Elective use of drop manholes is to be minimized and limited only to situations when <br />public wastewater is very deep, in areas of known high groundwater, or if dense <br />rock is encountered. The Project Engineer shall demonstrate the use of a drop <br />manhole shall not limit extension of gravity service to the wastewater basin. <br />A drop manhole is required where the drop through the manhole channel is <br />proposed to exceed 24 inches. External drop manholes are to be used as first <br />priority. Internal drop manholes may be used in situations where structural, utility or <br />topographical challenges prohibit the use of an external drop manhole. <br />3. Locations <br />Manholes shall be installed at the following locations: <br />• End of each main line, <br />• At all changes in grade, size or alignment (vertical and horizontal), <br />• At distances not greater than 400 feet. Greater spacing may be permitted in <br />large diameter wastewater lines as approved by the City. <br />Manholes shall be positioned outside normal wheel travel paths (centered in the lane <br />or between lanes) and outside the center of an intersection where the turning path <br />of vehicles may place a wheel path over them. <br />4. Size and Materials <br />See the Standard Specifications for Construction and Standards Drawings for <br />required manhole type, size and material properties. <br />5. Shallow Manholes <br />Public Improvement Design Standards Manual, 2016 Page 2-46 <br />