(a) These design criteria are not intended to cover extraordinary situations. Deviations will be allowed and may be required in those instances when considered justified by the Public Works Director and/or County Sanitary Engineer.
(b) Design Factors. Sewer capacities shall 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. Sewers shall be designed for the total tributary area using the criteria in Table 5-3.
DEVELOPMENT TYPE | FLOWS |
1-family and 2-family dwellings | 0.2 c.f.s./acre |
1-2 story apartments | 0.2 c.f.s./acre |
3-6 story apartments | 0.2 c.f.s./acre |
Commercial-small store, offices Commercial-shopping centers High-rise | 0.2 c.f.s./acre 0.2 c.f.s./acre As directed by County Sanitary Engineer |
Industrial | As directed by County Sanitary Engineer |
Note: 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 the design factor of .01 c.f.s./acre for an area of 1,000 acres unless otherwise directed by the Public Works Director and/or the County Sanitary Engineer. | |
(c) Size. The diameter of sewers proposed shall not exceed the diameter of the existing or proposed outlet, whichever is applicable, and shall be no less than eight (8) inches.
(d) Minimum Slope. All sewers shall be designed to give mean velocities, when flowing full, of not less than 2.0 feet per second and not greater than 10.0 feet per second. All velocity and flow calculations shall be based on the Manning Formula using an “n” value of 0.013.
(e) Alignment. All sewers shall be laid with straight alignment between manholes, unless otherwise directed or approved by the Public Works Director.
(f) Manholes. 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. 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 Public Works Director.
(g) Sewerage Location. Sanitary sewers shall be located within street or alley rights-of- way unless topography dictates otherwise. When located in easements on private property, there shall be access 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 right-of-way when possible.