A. Plans: The plans for all sewer lines, sewage lift stations, sewage treatment facilities, shall be designed in accordance with the City's approved design standards. All plans will be signed, and sealed by a registered professional engineer licensed in the state of Idaho.
B. Compliance With State Requirements: All sewer lines, lift stations, sewage treatment facilities, etc., shall be designed in accordance with Idaho DEQ.
C. Minimum Size: Minimum sanitary sewer main size shall be eight inch (8") diameter. Minimum storm drain size shall be eight inch (8") diameter. Larger sizes shall be as required by the City's overall sewer system master plan or as are 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 size shall be four inch (4") diameter.
D. Pressure Sewer Lines: Pressure sewer lines shall be a minimum of six inch (6") diameter with a cleanout every five hundred feet (500').
E. Depth: In general, sewers shall be sufficiently deep so as to receive sewage from basements and to prevent freezing. Sewer lines shall have at least five feet (5') of cover (from the top of sewer line pipe to the ground or street surface) unless a special design is approved by the City Engineer whereby the sewer line is protected from freezing by special means or methods and the sewer is protected from "heaving" by the installation of crushed gravel backfill material under, around, and over the pipe.
F. Slope: All sewer mains shall be designed and constructed to provide mean velocities, when flowing full, of not less than 2.0 feet per second. All sewer service lines (side sewer) shall be designed and constructed to provide mean velocities, when flowing full, of not less than 3.0 feet 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 fps 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 report his 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.
G. 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.
H. 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 to 10 degrees | Regular pipe slope |
10 to 45 degrees | 0.05 feet |
45 to 90 degrees | 0.10 feet |
I. Lateral Sewer Line Connections At Manholes: Lateral sanitary sewer lines shall not enter a manhole at the elevation appreciably higher than the sewer main line. The flow line(s) of any lateral line(s) shall be positioned with the manhole as follows:
The flow line of the main sewer line shall be at least 0.05 feet below the flow line of any of the lateral sewer lines entering the manhole. Where the diameter of the main line and the lateral line differ by less than 0.05 feet, the top of the lateral line shall be positioned even with the top of the main line on its high (inlet) side.
Where the diameter of the main and lateral differ by 0.05 of a foot or more, the 0.8 depth points of the two (2) sewer line inverts shall be positioned at the same elevation.
Where a lateral sewer line would enter a manhole at an elevation of four feet (4') 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.
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.
J. Location Of Lines: Sanitary sewer lines and water lines shall, wherever possible, be located on opposite sides of the street. Preferably, water lines shall be located thirteen feet (13') west or north of the street centerline and the sanitary sewer at thirteen feet (13') east or south of the street centerline. Where storm drains are needed these shall preferably be located along the street centerline. The above referenced locations and dimensions may be varied to accommodate unusual circumstances; however, a ten foot (10') (out to out) horizontal separation between water line facilities and sewer facilities (either sanitary or storm) and an eighteen inch (18") (out to out) vertical separation between said facilities shall always be maintained unless a specific variance to this requirement is obtained from the City Engineer. The applicable separation requirements of the state health department shall also be complied with.
K. Drawings: All drawings shall be on linen or mylar in pencil or ink and of such quality that they clearly show the dimensions, locations, 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 by station or other means of horizontal location. Sewer lines shall be shown in both plan and profile unless the length of said sewer lines or sewer line extensions is so short that the City Engineer 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 Engineer 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 inch = 50 feet or 1 inch = 40 feet) to provide the clarity and completeness needed on the drawings.
L. Approval By City: The design of all sewer lines and all sewer line plans must be approved by the City Engineer. (Ord. 543, 5-5-2009; amd. Ord. 2021-621, 9-2-2021)