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480 <br /> <br />B. SEWER COLLECTION SYSTEMS <br /> <br />1. DESIGN - GRAVITY SYSTEMS <br /> System shall be designed on the basis of an inflow rate of 400 gallons <br /> per day per single family residential unit. <br /> <br />Non residential flows shall be determined by the Design Engineer, in <br />accordance with state guidelines. <br /> <br />Minimum line size shall be 8 inches. <br /> <br />Maximum spacing between manholes shall be 400 feet for sewers 15" <br />diameter or less. With sewers 18" or larger, the spacing may be <br />increased if approved by the County Engineer. <br /> <br />Minimum cover for PVC pipe is 3 feet. <br /> <br />Maximum depth for PVC pipe is 18 feet. <br /> <br />Minimum slope for 8 inch pipe is 0.40%. <br /> <br />Maximum desired slope is 10.0%. When velocities exceed 15 feet per <br />second, special provisions must be incorporated to assure the <br />stability of the pipe. <br /> <br />A drop manhole is required when the difference in elevation between <br />the influent and effluent pipes exceeds 2.0 feet. <br /> <br />Minimum desired fall across a manhole is 0.20 feet. Ail inverts shall <br />be formed and sloped so that the fall from the influent invert to the <br />paved invert shall not exceed 0.5'. <br /> <br />Locate all street sewers within the asphalt portion of the street if <br />curb and gutter is to be installed or from top of shoulder to top of <br />shoulder if open ditches are to be used. <br /> <br />Minimum right-of-way width for off-street sewers is 20 feet. <br /> <br />Ail design shall be strictly in accordance with the standards and <br />requirements of the North Carolina Department of Natural Resources and <br />Community Development, Environmental Management Division. <br /> <br />DESIGN - LIFT STATIONS AND FORCE MAINS <br />Lift stations shall be designed as duplex systems. <br /> <br />Pumps shall be submersible type with piping and discharge base <br />permanently mounted in the wet well. <br /> <br />Each of the duplex pumps shall be designed to pump the full design <br />flow. <br /> <br />Each sewer line discharging into a wet well shall discharge into an <br />aluminum trash basket with an aluminum guide rail. <br /> <br />Any lift station within a development that discharges into the gravity <br />system of the County must have an approved meter installed in the <br />discharge line of the station for the purpose of measuring the waste <br />flow. <br /> <br />Force mains shall be designed to provide minimum velocity of 2.0 feet <br />per second. <br /> <br />An automatic air relief valve shall be placed at each high point in <br />the force main. <br /> <br />Emergency power connections shall be provided to enable the mobile <br />generator owned by the County to operate the lift station in times of <br />emergency. <br /> <br /> <br />