The following regulations shall apply to storm and sewer details on the preliminary plan:
(a) Storm Sewers. Storm sewers are to be closed conduits which convey stormwater run-off from a drainage area to an outlet. Storm sewers are to be designed to carry the peak rate of run-off from a design storm without having ponding of water. The storm sewers do not have to be designed to carry all of the run-off during infrequent major storms fast enough to avoid the local ponding of water on the streets or the overland run-off. The grades of the streets and the development of a major storm surface drainageway plan shall be considered while designing the improvements for the subdivision. Storm sewers shall be designed with the following minimum requirements:
(1) The peak design discharge flow rates shall be determined using the Rational Method for drainage areas of less than 200 acres. The basic formula for the Rational Method is: Q=CiA.
(2) Storm sewer pipes shall be sized to carry a ten-year storm without flowing under pressure. However, this requirement for ten-year storm sewer pipes shall not apply to the existing outlet pipe originally planned to serve additional areas with future extensions. The following locations are areas where the ten-year storm criteria shall not require construction of the outlet storm sewer:
A. Greenbriar Subdivision, #2 and higher
B. Robin Park, #8 and higher
C. Maslyk Subdivision, #1 and #2
D. Hampton Drive and eastward
In no event shall this exception be construed to mean that any subdivisions given preliminary approval by the Elyria City Planning Commission after the effective date of these Regulations shall be serviced internally by less than a ten-year size storm sewer pipe.
(3) The rainfall intensity ("i" in the rational method), in inches per hour, expressed for different times of concentration, shall be as follows:
Concentration Time | Storm Frequency | |||||
Concentration Time | Storm Frequency | |||||
2 Year | 5 Year | 10 Year | 25 Year | 50 Year | 100 Year | |
5 Minutes | 4.40 | 6.45 | 7.85 | 9.25 | 11.00 | 12.45 |
10 Minutes | 3.50 | 4.75 | 5.60 | 6.50 | 7.40 | 8.50 |
15 Minutes | 2.80 | 3.70 | 4.25 | 5.04 | 5.85 | 6.15 |
20 Minutes | 2.30 | 3.00 | 3.50 | 4.15 | 4.70 | 5.20 |
30 Minutes | 1.75 | 2.35 | 2.70 | 3.81 | 3.70 | 4.00 |
40 Minutes | 1.40 | 1.90 | 2.25 | 2.60 | 3.10 | 3.40 |
50 Minutes | 1.35 | 1.75 | 2.00 | 2.40 | 2.75 | 2.90 |
60 Minutes | 1.20 | 1.65 | 1.85 | 2.00 | 2.45 | 2.70 |
(4) The minimum pipe slope shall be the slope determined by finding the slope that produces an average velocity of flow of three feet per second for a two-year storm.
(5) The minimum storm sewer pipe diameter shall be twelve inches.
(6) The maximum allowable velocity in a pipe or at an outlet point shall be twelve feet per second.
(7) The minimum cover for a storm sewer pipe and a house storm lateral pipe shall be one foot of clearance between the bottom of the pavement's granular base to the top of the outside of the pipe.
(8) The hydraulic design of the storm sewers shall be based on the Manning equation.
(9) The roughness coefficient, Mannings "n", shall be 0.013 for concrete pipes. Other materials, if approved for use by the City Engineer, shall have "n" values as published in the American Society of Civil Engineering Manual on Engineering Practice No. 37.
(10) The storm sewer pipe shall be laid on a straight line on a straight grade, except for radius pipe.
(11) Radius pipe shall be used for changes of direction of more than forty-five degrees on pipes of thirty-six inches in diameter or larger.
(12) Manholes or access structures shall be located at junctions of conduits (including the street inlet connections to the storm sewer), at changes in direction, at changes in slope and near the midpoint of radius pipe locations. The maximum spacing of manholes or access structures shall be 400 feet for pipes forty-two inches in diameter and smaller, and 575 feet for pipes forty-eight inches in diameter and larger.
(13) Street inlets shall be located at not more than 400 feet from high points or from previous inlets on a grade sloping in the same direction.
(14) All grades shall be designed such as to divert surface waters and surface drainage into underground storm drainage systems and to prohibit the diversion of water to adjacent lots.
(b) Sanitary Sewers; Details of Design and Construction. Sanitary sewers shall be designed with the following minimum requirements:
(1) Minimum size of sewer. No public gravity sanitary sewer conveying raw wastewater shall be less than eight inches in diameter.
(2) Depth of sewer. In general, sanitary sewers shall be sufficiently deep to receive wastewater from basements and to prevent freezing. Insulation shall be provided for sewers and building sewer laterals that cannot be placed at a depth sufficient enough to prevent freezing.
(3) Minimum slope of sewer. All sewers shall be designed and constructed to give mean velocities, when flowing full, of not less than two feet per second, based on the Manning formula using an "n" value of 0.013. The following are the recommended minimum slopes which shall be provided. However, slopes greater than these are more desirable.
Sewer Size | Minimum Slope in Feet per 100 Feet |
Sewer Size | Minimum Slope in Feet per 100 Feet |
8 inches | 0.40 |
10 inches | 0.28 |
12 inches | 0.22 |
14 inches | 0.17 |
15 inches | 0.15 |
16 inches | 0.12 |
18 inches | 0.10 |
21 inches | 0.10 |
24 inches | 0.08 |
(4) Minimize solids deposition. The pipe diameter and slope shall be selected to obtain the greatest practical velocities to minimize settling problems. Oversized sewers shall not be utilized to justify using flatter slopes. The actual depths and velocities at minimum, average and design maximum day and peak-hour flow for each design section of the sewer, shall be calculated by the design engineer and shall be included with the plans submitted to the City for review.
(5) Slope between manholes. Sewers shall be laid with a uniform slope between manholes.
(6) High-velocity protection. Where velocities greater than fifteen feet per second are attained, special provisions shall be made to protect against displacement by erosion and impact.
(7) Alignment of sewers. Sewers twenty-four inches in diameter and smaller shall be laid with straight alignment between manholes. Straight vertical alignment shall be controlled by a laser beam. Curvilinear alignment of sewers larger than twenty-four inches may be considered on a case-by-case basis.
(8) Change in pipe size. When a sewer joins a larger one, the invert of the larger sewer should be lowered sufficiently to maintain the same energy gradient. An approximate method for securing these results is to place the eight-tenths depth point of both sewers at the same elevation.
(9) Sewer extensions. Main trunk sewer extensions shall be designed (grade and size) for projected service area design flows.
(10) Materials. Sanitary sewers shall be constructed of either PVC, clay or DI cement-lined pipe.
(11) Installation. The trenching, bedding, haunching, initial backfilling and final backfilling shall be completed as per City specifications, as established in the Engineering Division office.
(12) Deflection tests. A deflection test shall be performed on all flexible pipes not less than sixty days after installation. No pipe shall exceed a deflection of five percent. If the deflection exceeds five percent, replacement shall be accomplished in accordance with the requirements of the specifications. The deflection test shall be conducted with a mandrel having a diameter of not less than ninety-five percent of the inside sewer diameter. The test shall be performed without any mechanical pulling devices.
(13) Leakage tests. A leakage test, with either water or low pressure air testing methods, shall be completed as per City specifications, as established in the Engineering Division office.
(14) Manhole locations. 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 sixteen inches or less in diameter, and 500 feet for all sewers eighteen to thirty inches in diameter. Greater spacing, up to 600 feet, may be permitted by the City Engineering Division on sewers larger than thirty inches in diameter.
(15) Drop manholes. Drop manholes shall be constructed with an outside drop connection when the sewer entering the manhole is at an elevation of twenty-four inches or more above the manhole invert. The entire outside drop connection shall be encased in concrete.
(16) Manhole diameter. The minimum inside diameter of manholes shall be forty-eight inches. Larger diameters are required for larger sewers. A minimum access diameter of twenty-one inches shall be provided.
(c) Sanitary Sewage Lift Stations.
(1) Where required to provide the minimum depth for sanitary sewers, a sanitary sewage lift station shall be constructed, unless other provisions for sewage flow are approved by the Planning Commission.
(2) Sanitary sewage lift stations shall be located on permanent easements outside of the minimum right-of-way required for street purposes. The stations, for maintenance purposes, shall be accessible by a paved driveway to the station and shall include an off-street parking area when located along arterial streets.
(3) The sanitary sewage lift station shall have not less than two pumps, each of which shall have the design capacity to pump sewage at the peak design flow rate, based on the Ohio Environmental Protection Agency's recommended flow volumes. The lift station shall be able to handle the peak design flow with the largest pump out of service.
(4) The wet well storage volume shall be large enough that, after failure of the pump to operate for any reason, sewage may continue to flow for two hours at average design flow rates into the system (including the sewer line) before reaching the elevation point in the crown of the sewer line where the lowest house lateral is connected.
(5) Except for individual home pumps used for pressure sewer systems, the sanitary sewage lift station shall be designed as suction lift. The suction lift station design requirement may be modified by the City Engineer provided that there is sufficient design and operational documentation available to substantially justify that an alternative pump design is appropriate for the specific conditions. The determination by the City Engineer as to the appropriateness of a suction lift design or an alternative design resides entirely with the City Engineer and is not subject to an appeal.
(6) Sanitary sewage lift stations shall have a permanent stand-by power generator or secondary source of electrical power. To be considered a secondary source of electrical power, it must come from a different utility substation. Any generator furnished shall be driven by either a diesel or natural gas engine.
(7) Sanitary sewage lift stations shall be equipped for connection to the City's SCAD A system and alarm sending unit.
(Ord. 97-297. Passed 12-15-97; Ord. 2018-98. Passed 7-9-18.)