A. Plans: The plans for all sewer lines, sewage lift stations, sewage treatment facilities, etc., shall be designed, signed and sealed by a registered professional engineer licensed in the State, as the City deems necessary.
B. State Health Department Requirements: All sewer lines, lift stations, sewage treatment facilities, etc., shall be designed and approved in accordance with State Health Department requirements.
C. Minimum Size: Minimum sanitary main size shall be eight inch (8") diameter, unless a special design is approved by the City where the sewer line may be reduced. Minimum storm drain size shall be eight inches (8") in diameter. Larger sizes shall be required by the City's overall sewer system master plan or as needed to provide adequate sewage-carrying capacity for the area (and surrounding developable area) being developed and/or annexed to the City. Minimum building service line (side sewer) size shall be four inches (4") in diameter.
D. Generally: In general, sewers shall be sufficiently deep so as to receive sewage from basements and to prevent freezing. Sewer lines shall have at least three feet (3') of cover (from the top of the sewer line pipe to the ground or street surface) unless a special design is approved by the City whereby the sewer line is protected from freezing by special means or methods and the sewer is protected from "heaving" by installation of crushed gravel backfill material under, around and over the pipe.
E. Design And Construction: All sewer mains shall be designed and constructed to provide mean velocities, when flowing full of not less than two feet (2') per second. All sewer service lines (side sewers) shall be designed and constructed to provide mean velocities, when flowing full, of not less than three feet (3') per second. The following are minimum slopes which should be provided; however, slopes greater than these are desirable:
Sewer Size | Minimum Slope In Feet Per 100 Feet |
Sewer Size | Minimum Slope In Feet Per 100 Feet |
4 inch | 2.00 |
6 inch | 1.00 |
8 inch | 0.40 |
10 inch | 0.28 |
12 inch | 0.22 |
15 inch | 0.15 |
18 inch | 0.12 |
21 inch | 0.10 |
24 inch | 0.08 |
27 inch | 0.067 |
30 inch | 0.058 |
36 inch | 0.046 |
Under special conditions, if detailed justifiable reasons are given, slopes slightly less than those required above (i.e., to provide 2.0 or 3.0 fsp velocity when flowing full) may be permitted. Such decreased slopes will only be considered where the depth of flow will be 0.3 of the diameter or greater for the design average flow. Whenever such decreased slopes are proposed, the design engineer must furnish with his or her report his or her computations of the depths of flow, in such pipes at the minimum and average rates of flow for a typical day.
Sewers shall be laid with uniform slopes between manholes (i.e., a manhole shall be constructed at each point where the sewer line slope or grade changes).
F. Manholes: Manholes shall be located no more than four hundred feet (400') apart on lines fifteen inches (15") in diameter or smaller. Manholes may be located up to six hundred feet (600') apart on lines larger than fifteen inches (15") in diameter. Manholes shall be installed at all locations where sewer lines eight inches (8") in diameter or larger intersect, join together or make a bend. All dead-end sewer lines shall have a manhole installed on the end thereof or a lamp well where approved by the Superintendent.
G. Sewer Mainline Drop Through Manholes: The flow line of the main sewer line as it enters and leaves any manhole shall be dropped as follows:
Mainline Bend Of | Drop Of |
0 - 10 degrees | Regular pipe slope |
10 - 45 degrees | 0.05 feet |
45 - 90 degrees | 0.10 feet |
H. Lateral Sewer Line Connections At Manholes: Lateral sanitary sewer lines shall not enter a manhole at an elevation appreciably higher than the sewer mainline. The flow line(s) of any lateral line(s) shall be positioned within the manhole as follows:
1. The flow line of the main sewer line shall be at least 0.05 foot below the flow line on any of the lateral sewer lines entering the manhole.
2. Where the diameter of the main line and the lateral line differ by less than 0.5 foot, the top of the lateral line shall be positioned even with the top of the main line on its highest (inlet) side.
3. Where the diameter of the main and lateral differ by 0.5 foot or more, the two (2) sewer line inverts shall be positioned at the same elevation.
4. Where a lateral sewer line would enter a manhole at an elevation of three feet (3') or more above the main sewer line, "drop manhole" construction shall be utilized to locate or position the flow line of the lateral line (in relation to that of the main line) as indicated above.
5. Where a lateral line would enter a manhole at an elevation of less than three feet (3') above the main sewer line, the grade or slope of the lateral shall be adjusted so that its flow line is located (in relation to that of the main line) as indicated above.
Individual building service lines may not enter manholes; except that no more than two (2) individual building service lines may enter a "dead-end" manhole (a manhole on the upstream and permanent end of a sewer line); and provided further, that the individual building service lines must enter the manhole at such elevation that the top of the service line is level with the top of the sewer main line and that the poured-in-place concrete floor of the manhole brings the flow lines of the service lines into the flow line of the main line in a smooth continuous manner.
I. Location Of Sewer And Water Lines: Sanitary sewer lines and water lines shall, wherever possible, be located on opposite sides of the street, a ten foot (10') (out-to-out) horizontal separation between water line facilities and sewer line facilities (either sanitary or storm) and an eighteen inch (18") (out-to-out) vertical separation between said line facilities shall always be maintained, unless a specific variance to this requirement is obtained from the City. The applicable separation requirements of the Idaho Health Department shall also be complied with.
J. Drawings: All drawings shall be on linen or mylar in pencil or ink and of such quality that they clearly show the dimensions, location, sizes, etc., of all facilities represented thereon. All sewer line manholes, inlet boxes, building service lines, etc., shall be clearly shown and identified by name and station or other means of horizontal location. Sewer lines shall be shown both plan and profile unless the length of said sewer line or sewer line extension is so short that the City waives this requirement. If a profile of the sewer line is not provided, it shall be located in the vertical plane by elevations on the flow line of the pipe at all manholes, inlet boxes, etc., and at other such locations and intervals as the City may require. Drawings shall be drawn on a scale of one inch equals one hundred feet (1" = 100') unless the amount of detail, topography, etc., necessitates their being drawn on a larger scale (i.e., 1" = 40') to provide the clarity and completeness needed on the drawings.
K. Approval Of City: The design of all sewer lines and all sewer system plans must be approved by the City. (Ord. 655, 9-27-1994)