(A) Deviations. 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.
(B) Design factors.
(1) Sanitary sewer systems should be designed for the ultimate tributary population. Due 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 flows. 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 following criteria.
Cubic Feet per Second (cfs)/Acre |
Cubic Feet per Second (cfs)/Acre | |
Apartments | |
One- and two-story | .02 |
Three- through six-story | .03 |
Commercial | |
High rise | As directed by the City Engineer |
Industrial | As directed by the City Engineer |
Shopping centers | .02 |
Small stores, offices, and miscellaneous businesses | .02 |
One- and two-family dwellings | .02 |
(2) These design factors shall apply to watersheds of 300 acres or less. Design factors for watersheds larger than 300 acres and smaller than 1,000 acres shall be computed on the basis of a linear decrease from the applicable design factor for an area of 300 acres to a design factor of .01 cfs/acre for an area of 1,000 acres, unless otherwise directed by the City Engineer. Design factors for watersheds larger than 1,000 acres shall be .01 cfs/acre unless otherwise directed by the City Engineer.
(C) Maximum size. 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.
(D) Minimum size. No public sewer shall be less than eight inches in diameter.
(E) Minimum slope. All sewers shall be designed to give mean velocities, when flowing full, of not less than 2.7 feet per second. All velocity and flow calculations shall be based on the Manning Formula using an N value of 0.013. The slopes shall be the minimum for the size indicated. Exceptions to these slopes shall be made at the upper end of lateral sewers serving under 30 houses. Said sewers shall have a minimum slope of 0.76%. Where lateral sewers serve less than ten houses, the minimum slope shall be not less than 1%.
Minimum Slopes for Sewer Size Indicated | |
Sewer Size (in.) | Minimum Slope (in ft./l00 ft.) |
Minimum Slopes for Sewer Size Indicated | |
Sewer Size (in.) | Minimum Slope (in ft./l00 ft.) |
8 | 0.60 |
10 | 0.44 |
12 | 0.36 |
15 | 0.28 |
18 | 0.24 |
21 | 0.20 |
24 | 0.16 |
(F) Alignment. All sewers shall be laid with straight alignment between manholes, unless otherwise directed or approved by the City Engineer.
(G) Manhole location. 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 400 feet for sewers 15 inches and smaller, and 500 feet for sewers 18 inches in diameter and larger.
(H) Manholes. The difference in elevation between any incoming sewer and the manhole invert shall not exceed 12 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. Inside drop manholes will require special considerations. However, in no case shall the minimum clear distance be less than that indicated herein. 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 shall be 0.2 feet.
(I) Sewer locations. Sanitary sewers shall be located within a street or right-of-way, unless topography dictates otherwise. When located in easements on private property, access shall be to manholes. A manhole shall be provided at each street or crossing. End lines shall be extended to provide access from a street or alley right-of-way where possible. Imposed loading shall be considered in all locations. Not less than six feet of cover shall be provided over the top of a pipe in streets and rights-of-way, and not less than three feet shall be provided in all other areas.
(J) Cleanouts. Cleanouts will not be permitted.
(K) Water supply interconnections. There shall be no physical connection between a public or private potable water supply system and a 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.
(L) Relation of sewers to water mains. A minimum horizontal distance of ten 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.
(Prior Code, § 1246.04)