(A) General. The applicant shall install sanitary sewer facilities in the method prescribed by the city construction standards and specifications. All plans shall be designed in accordance with the rules, regulations and standards of the local government, State Health Department, United States Environmental Protection Agency and other appropriate agencies.
(B) Sanitary sewerage facilities with public sanitary sewer systems.
(1) Sewers shall be installed to serve each lot and to grades and sizes required by the City Engineer. No individual disposal system or treatment plant (private or group) shall be permitted except as noted herein.
(2) The Metro Area Planning Commission may allow the developer to install a central sewerage system for the development or individual disposal system if the development is more than 3,000 feet from the nearest public sewer system (measured from subdivision boundaries), or if the owner of the public sewer system will not allow the developer to connect to the system. This provision shall not be applicable to minor subdivisions with an average lot size greater than two acres. Privately owned systems shall meet the requirements of the health officer and local government engineer.
(C) Design criteria for sanitary sewers.
(1) (a) The design criteria presented herein are not intended to cover extraordinary situations. Deviations will be allowed and may be required in those instances where considered justified by the local government engineer.
(b) Sanitary sewers should be designed for the ultimate tributary populations. Due consideration should be given to current and anticipated zoning and approved sewerage master plans. The capacity of sewage collection systems should be adequate to hold the anticipated maximum hourly quantity of sewerage and industrial waste together with an adequate allowance for infiltration and other extraneous flow. As a unit flow, two-hundredths cubic foot per second per acre (with an appropriate increase for areas where apartment buildings or high rises are planned) or 450 gallons per day per capita (total tributary population must be estimated) should be adequate. Design flows for areas larger than 300 acres should be adequate if the unit design factors are one-hundredth cubic foot per second per acre or 300 gallons per day per capita.
(2) Sanitary sewer system shall consist of trunk line sewers, lateral lines sewers, service connections, pump stations and force mains. Lateral sewers shall not be less than eight-inch nominal internal diameter except when the ultimate number of lots served is four or less and the maximum length of lateral line is 300 feet. The size of trunk lines, force mains and pump stations should be determined by the capacity and flow considerations described previously and the directions of the City Engineer. The diameter of proposed sewers shall not exceed the diameter of the existing or proposed sewer unless otherwise approved by the City Engineer.
(3) Prior to the issuance of any building permits, the developer shall pay the owner of the public sewer any required fees for connecting to the sewage system.
(4) All sewers should be designed to maintain a mean velocity of not less than two and five-tenths feet per second when flowing full and shall, as a minimum, be designed to maintain a mean velocity of not less than two feet per second when flowing full. Velocity and flow calculation shall be based on the Manning formula using an “n” value of 0.013, or as directed by the City Engineer. Lateral lines that will not be extended and serve less than the equivalent of ten houses shall be sloped not less than 1%. Lateral lines that will not be extended and serve less than the equivalent of 25 houses and greater than the equivalent of ten houses should be sloped not less than 0.76% where feasible. Sewers shall be designed so the velocities will not exceed ten feet per second at average flows or shall be of a special design approved by the City Engineer. Sewers shall be provided with protection against displacement when laid on slopes greater than 7%.
Minimum Slopes for Sewer Size Indicated | ||
Sewer Size (Diameter in Inches) | Minimum Design Slope in Feet Per/100 Feet | Minimum Slope in Feet Per/100 Feet |
8 | 0.52 | 0.40 |
10 | 0.39 | 0.29 |
12 | 0.30 | 0.22 |
15 | 0.22 | 0.15 |
18 | 0.18 | 0.12 |
21 | 0.15 | 0.10 |
24 | 0.12 | 0.08 |
(5) Pump stations and force mains will be permitted only under extraordinary conditions of topography and distance to the public sewer system. Pump stations shall be designed to meet the reliability criteria established by the City Engineer.
(6) All sewers shall be designed with straight alignment between manholes, unless otherwise directed or approved by the City Engineer.
(7) 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. In lieu of manholes, the City Engineer may approve inspection cleanouts at end lines where appropriate.
(8) The difference in elevation between any incoming sewer and the manholes invert shall be less than 24 inches except where required to match crowns. The use of drop manholes will require approval by the City Engineer. When sewers are increased in size, or when a smaller sewer joins a larger one, the invert of the larger one shall be lowered sufficiently to maintain the same energy gradient. The minimum drop through manholes shall be one-tenth foot.
(9) Sanitary sewers shall be located within public utility easements, streets or alley rights-of-way, according to the policy of the owner of the sewerage system, the directions of the City Engineer and topography characteristics. When sewers with two or more consecutive manholes located in easements on private property are proposed, access lanes should be provided to all manholes. A manhole should be provided at each street or alley crossing. End lines shall be extended to provide access from street or alley right-of-way where possible. Imposed loading shall be considered in all locations. No less than four feet of cover should be provided over top of pipe. In no event shall less than two and one-half feet of cover be provided unless special protection is provided for the pipe.
(10) 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.
(11) A minimum horizontal distance of ten feet shall be maintained between parallel water and sewer lines. The top of the sewer pipe should be a minimum of two feet lower than the bottom of the water line at points where they cross. In the event the vertical or horizontal clearance cannot be maintained, the sewer line shall be constructed out of material pressure rated for a minimum working pressure of 150 pounds per square inch. When the horizontal separation cannot be maintained, the sewer shall be laid in a separate trench from the water line and at a lower elevation.
(12) Inverted siphons shall be permitted only under extraordinary conditions.
(13) The width of easements in which sanitary sewers are located shall be the greater of 12 feet or the width of the sewer plus ten feet.
(D) Plan details.
(1) The plan and profile along the line of all sewers to be constructed shall be detailed. The plan and profile shall show all special features. Stream crossings and sewer outlets shall be shown on the profiles with the elevations of the streambed and, if known, of the normal and extreme high and low water levels. Profiles should have a horizontal scale of not more than 100 feet to the inch and a vertical scale of not more than ten feet to the inch. Both scales shall be clearly shown on the plan and profile. All known and existing and proposed structures both above and below the ground which may interfere with the proposed construction shall be shown both in plan and profile. The location of service connections shall be noted. The plan shall include a noted reference to the construction conditions.
(2) Figures showing the manhole stationing, size of sewers, surface and sewer invert elevations of all sewers at each manhole and the grade and length of all sewers between each two adjacent manholes shall be shown on the profiles. The dimensioned location of the sewer lines shall be shown on the plan.
(3) The details of all sewer appurtenances such as manholes, drop manholes, inspection chambers, as well as of any special appurtenances, shall be included in the plans or a reference shall be made on the plans to the standard plans of the city.
(Prior Code, § 11-7-5) (Ord. 594, passed 8-5-1997)