A. Sanitary sewer systems should be designed for the ultimate drainage basin population. Consideration should be given to current zoning regulations, and approved planning and zoning reports where applicable. Sewer capacities should be adequate to handle the anticipated maximum hourly quantity of sewage and industrial waste together with an adequate allowance for infiltration and other extraneous flow. The unit design flows presented hereinafter should be adequate in each case for the particular type of development indicated. Sewers shall be designed for the total tributary area using the criteria codified as Table 4 at the end of this chapter.
B. The design factors codified in Table 4 shall apply to watersheds of three hundred acres or less. Design factors for watersheds larger than three hundred acres and smaller than one thousand acres shall be computed on the basis of a linear decrease from the applicable design factor for an area of three hundred acres to a design factor of .01 cfs/acre for an area of one thousand acres unless otherwise directed by the city engineer. Design factors for watersheds larger than one thousand acres shall be .01 cfs/acre unless otherwise directed by the city engineer.
1. The diameter of sewers proposed shall not exceed the diameter of the existing or proposed outlet, whichever is applicable, unless otherwise approved by the city engineer;
2. No public sanitary sewer line shall be less than eight inches in diameter, unless sewer line is less than four hundred feet long and cannot be extended;
3. All sewers shall be designed to give mean velocities, when flowing full, of not less than two feet per second. All velocity and flow calculations shall be based on the Manning Formula. The slopes shall be minimum for the size indicated;
4. All sewers shall be laid with straight alignment between manholes, unless otherwise directed or approved by the city engineer;
5. Manholes shall be installed at the end of each line; at all changes in grade, size or alignment; at all intersections; and at distances not greater than three hundred feet for sewers less than eighteen inches, and four hundred feet for sewers eighteen inches in diameter and larger;
6. The difference in elevation between any incoming sewer and the manhole invert shall not exceed twelve inches except where required to match crowns. The use of drop manholes will require approval by the city engineer. The minimum inside diameter of the manholes shall conform to those specified by the city engineer. When a smaller sewer joins a larger one, the crown of the smaller sewer shall not be lower than that of the larger one. The minimum drop through manholes at bends and turns shall be 0.2 feet;
7. Manhole covers shall be sealed covers with inverted vented dishes;
8. Sanitary sewers shall be located within street or alley rights-of-way unless topography dictates otherwise. When located in easements on private property, access shall be provided to all manholes. A manhole shall be provided at each street or alley crossing. End lines shall be extended to provide access from street or alley rights-of-way where possible. Imposed loading shall be considered in all locations. Not less than 3.0 feet of cover shall be provided over top of pipe in street and alley rights-of- way or other areas;
9. Cleanouts and lampholes will not be permitted;
10. There shall be no physical connection between a public or private potable water supply system and sewer which will permit the passage of any sewage or polluted water into the potable supply. Sewers shall be kept removed from water supply wells or other water supply sources and structures;
11. A minimum horizontal distance, from outside to outside of pipewall, of six feet shall be maintained between parallel water and sewer lines. At points where sewers cross water mains, the sewer shall be constructed of cast iron pipe or encased in concrete for a distance of ten feet in each direction from the crossing, measured perpendicular to the water line. This will not be required when the water main is at least two feet above the sewer line;
12. These design criteria are not intended to cover extraordinary situations. Deviations will be allowed and may be required in those instances where considered justified by the city engineer.
(Ord. 1179 § 4.6(F))