Chapter 18.20
SANITARY SEWERS
Sections:
18.20.020 Sanitary sewer pipes.
18.20.030 Manholes and cleanouts.
18.20.040 Sanitary sewer alignment.
18.20.050 Sanitary sewer connections.
18.20.060 Wastewater pump stations.
18.20.070 Sanitary sewer system testing.
18.20.005 Generally.
This chapter provides information for the design of public sanitary sewers. Public sanitary sewer design plans are reviewed and approved by the engineering division.
Private sanitary sewers constructed on private property must be designed according to the Oregon Plumbing Specialty Code.
The following sanitary sewer design standards have been developed with the goals of proper sizing for current and future flows, correct installation for long life, ease of access for maintenance and repair while taking into account construction costs.
Compliance with these standards does not relieve the design professional of the responsibility to apply conservative and sound professional judgment. These are minimum standards and are intended to assist, but not substitute for, competent work by design professionals. The city may at its sole discretion, due to special conditions and/or environmental constraints, require more stringent requirements than would normally be required under these standards.
This chapter is intended to be consistent with and a supplement to the following documents:
|
APWA |
American Public Works Association |
|
ASTM |
American Society for Testing and Materials |
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OAR |
Oregon Administrative Rules |
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CBMC |
City of Coos Bay Municipal Code |
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OPSC |
Oregon Plumbing Specialty Code |
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DEQ |
Oregon Department of Environmental Quality Water Quality Program Rules1 |
1 Oregon Department of Environmental Quality, Water Quality Program Rules – Division 052
http://www.deq.state.or.us/regulations/rules.htm
Where conflict exists between these design standards and the above referenced documents, the most stringent requirements shall take precedence. [Ord. 479 § 1 (EDS § 4), 2016].
18.20.010 Design flows.
The entire basin to be served by a sanitary sewer must be taken into account when developing design flows for new or replacement sanitary sewers.
Flow calculations prepared by a professional engineer are required for all lines serving 10 or more residences and all commercial or industrial facilities with flows in excess of 3,600 gallons per day (gpd). Engineer prepared calculations for lesser thresholds may be required by public works staff based on known existing conditions in the downstream collection system. [Ord. 479 § 1 (EDS § 4.1), 2016].
18.20.020 Sanitary sewer pipes.
(1) Sanitary Sewer Pipe Material. The standard pipe material to be used for gravity sanitary sewers is green PVC meeting the requirements of ASTM D3034 SDR35. High-density polyethylene (HDPE) pipe with fused joints is also acceptable. All HDPE pipe shall be de-beaded. Minimum wall thickness class of HDPE pipe is SDR 26. Other pipe materials may be considered where appropriate and must be approved by public works. Tracer wire shall be a minimum 18-gauge minimum, solid copper wire with green 30-mil-thick HDPE insulation rated for direct burial, and shall be installed with all sanitary sewer pipes. Use waterproof splice at all connections.
Sanitary and storm sewer lines must have warning tape. The tape shall be six inches wide, four-mil-thick, APWA green, and reading “Caution Sewer Line Buried Below.”
(2) Sanitary Sewer Pipe Size. Sanitary sewers shall be sized to adequately handle the expected flows. The minimum sanitary sewer diameter is eight inches. For dead-end lines up to a maximum length of 250 feet, that have no possibility of future extension and serve less than six houses or have limited flow, six-inch lines will be allowed providing that they can be shown to have sufficient capacity and flow velocity. Manholes will be required at upstream end for maintenance purposes.
(3) Sanitary Sewer Pipe Slope. Sanitary sewers shall be sloped to provide a minimum velocity of two feet per second (fps) for the average daily flow using a Manning’s roughness coefficient of 0.013 or greater. In no case, unless approved by public works, shall the slope be less than shown in Table 4-1.
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Pipe Diameter (inches) |
Minimum Slope (%) |
|---|---|
|
6 |
0.75 |
|
8 |
0.40 |
|
10 |
0.40 |
|
12 |
0.40 |
Slopes shown are an absolute minimum. Calculations shall be provided to show that minimum flow velocity requirements can be met. Sizing pipes larger than needed for the anticipated flow to allow installation at a reduced slope is not acceptable. Sanitary sewer diameters may not be reduced in a downstream direction even if steeper slopes allow a smaller diameter pipe to have sufficient capacity for the design flow.
Flow velocities greater than 15 fps under daily peak flows should be avoided. A velocity over 15 fps in sanitary sewer pipes requires special consideration for pipe scour control (and manhole scour; see CBMC 18.20.030(4)). Pipe restraints or anchors may be required for pipe slopes in excess of 20 percent.
(4) Sanitary Sewer Depth. Sanitary sewers shall be installed with a minimum of 36 inches of cover from the top of the pipe to the finish surface. The depth should be sufficient to provide for access by gravity from all adjacent properties in the area whether proposed or existing. Sanitary sewer main depth shall be designed to avoid conflict with other existing and proposed utilities as provided in CBMC 18.20.040(2). Conflicts between sanitary sewer laterals and other utilities must also be taken into account in the design. All design must be in conformance with OAR 333-061-0050.
(5) Sanitary Sewer Laterals. Sanitary sewer laterals shall meet the requirements of the Oregon Plumbing Specialty Code. [Ord. 479 § 1 (EDS § 4.2), 2016].
18.20.030 Manholes and cleanouts.
(1) Location. Manholes shall be installed at the following locations:
(a) All changes of pipe size, direction, alignment and grade;
(b) At the upstream end of the pipe;
(c) Maximum spacing of 300 feet;
(d) Each intersection or junction of sanitary sewer mains;
(e) Any intersection of a service or private sewer of eight inches or larger;
(f) Manholes shall not be placed in the wheel path.
Manhole placement within the street right-of-way should allow easy access without blocking both traffic lanes. Manhole covers shall not be located in the normal wheel path for the street nor within a crosswalk. Place manholes to avoid surface runoff or stormwater ponding.
(2) Standard Manhole. Manholes shall be 48 inches in diameter for main sizes up to 24 inches. For line sizes in excess of 24 inches, the design engineer shall submit manhole designs. A minimum 0.1-foot drop in inverts across the manhole is required where the angle between the upstream and downstream pipe is less than 90 degrees. Provide at least a 0.2-foot drop in inverts where the outlet pipe is 90 degrees from the inlet pipe, or where manholes larger than 48 inches have been approved for use by public works. Designs for connections to existing manholes shall show the location of the cover and ladder and the elevations of all pipe inverts, channels, ledge and rim. When different size pipes enter/exit a manhole, the elevation of the crowns of the pipe shall match.
Flat top manholes should be used when there is less than six feet from the pipe invert to the top of the manhole.
(3) Drop Manhole. The maximum permitted channelized drop across a manhole is 24 inches. For drops in excess of 24 inches, a drop manhole is required. Inside drops are only permitted when adequate room is available within the manhole and when site conditions make an outside drop extremely difficult to construct. Only one inside drop is permitted in each manhole. Inside drops require approval by public works.
(4) Manhole Scour Protection. Internal manhole scour protection, such as HDPE flat plate (one-quarter inch thick), epoxy coating or energy dissipation mechanisms shall be provided whenever entering flows exceed 15 feet per second. Scour protection treatments require approval by the engineering division.
(5) Connections to Existing Manholes. When connecting new lines to existing manholes, the manhole wall must be core drilled cleanly, and grouted or otherwise sealed to prevent groundwater inflow and infiltration. [Ord. 479 § 1 (EDS § 4.3), 2016].
18.20.040 Sanitary sewer alignment.
Sanitary sewer lines shall have a straight alignment with a constant grade between manholes. Curved alignment will not be allowed unless there are no reasonable alternatives and must be approved by public works. Sanitary sewer alignment shall be in a street right-of-way whenever possible.
(1) Sanitary Sewer Easements. The minimum easement width for installations of storm and sewer with depths of cover of five feet or less (measured at the top of pipe) is 15 feet. The minimum easement width will be increased by 10 feet for each additional five feet of cover over five feet (rounded up). Easements shall be centered over the utility.
If due to topographic constraints the sanitary sewer must run along the alignment of a property line, adequate access must be provided. A minimum 15-foot-wide sanitary sewer easement is required for access and an adequate surface is required for physical access. The sanitary sewer alignment must be graded to permit travel by utility trucks and backhoes. The sanitary sewer alignment should be offset from the property line to avoid conflicts with survey monuments. The easement description must hold the city harmless for any damage to or removal of fences, retaining walls, trees or other improvements constructed in the easement area. Easements need to be shown on the final plat or recorded easement document prior to city acceptance.
Sewers in easements will be allowed only after all reasonable attempts to place the mains in the right-of-way have been exhausted. All sewers shall be centered in the easements.
(2) Clearance from Other Utilities. Separation of parallel water and sanitary sewer lines shall meet the requirements of OAR 333-061-0050.
Adequate separation is required from other utilities. All clearances listed in Table 4-2 are from edge of pipe to edge of pipe:
|
Utility |
Min. Distance (ft) |
|---|---|
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Cable TV |
5 |
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Gas |
10 |
|
Power |
10 |
|
Storm |
5 |
|
Telephone, Fiber Optic |
10 |
|
Utility |
Min. Distance (ft) |
|---|---|
|
Cable TV |
2 |
|
Gas |
2 |
|
Power |
2 |
|
Storm |
2 |
|
Telephone, Fiber Optic |
2 |
[Ord. 479 § 1 (EDS § 4.4), 2016].
18.20.050 Sanitary sewer connections.
In accordance with the Coos Bay Municipal Code, each residential, commercial or industrial building is required to have a separate connection to the public sanitary sewer. Exceptions are allowed per CBMC 13.15.170.
(1) Connection of Sanitary Sewer Laterals. Connection of sanitary sewer laterals to the public sanitary sewer main must conform to the standard details. The cost of new lateral connections or extensions is the responsibility of the property owner.
City responsibility for sanitary sewer maintenance is limited to public sanitary sewer mains. Sanitary sewer laterals from the point of connection, including the connection at the sanitary sewer main, back to the building are the responsibility of the property owner.
(2) Connection of New Sanitary Sewer Mains. Connections of new sanitary sewer mains to existing pipes must be done with a manhole. There is a possibility of surcharging in some existing sanitary sewer lines, particularly the interceptor. This must be taken into account when designing new connections and measures such as storage or backflow prevention constructed to avoid problems.
(3) Pretreatment Requirements for Sanitary Sewer Connections. Chapter 13.15 CBMC prohibits the introduction of mastics, oil, grease or petroleum products into the public sanitary sewer by any user connected to the sanitary sewer system. Industrial, commercial and/or retail operations, regardless of size, that generate petroleum/animal/vegetable fats, oils or grease (FOG) waste, must pretreat wastewater prior to discharging to the public sanitary sewer. Pretreatment systems are reviewed and approved by the State of Oregon Plumbing Official. Ongoing maintenance and repair of pretreatment systems to ensure proper function is the responsibility of the property owner. [Ord. 479 § 1 (EDS § 4.5), 2016].
18.20.060 Wastewater pump stations.
Pump stations will be evaluated on a case-by-case basis by public works. Pump station design plans require DEQ approval in addition to city approval.
Wastewater pump stations must be designed by an Oregon registered professional engineer and must meet DEQ standards for design and construction of wastewater pump stations. Operation and maintenance manuals meeting DEQ guidelines must also be provided. Contact public works for additional specifications on pump station controls and appurtenances required by the city. [Ord. 479 § 1 (EDS § 4.6), 2016].
18.20.070 Sanitary sewer system testing.
All new sanitary sewer pipes and manholes must be tested for water tightness prior to city acceptance, using a DEQ-approved method. (Refer to Appendix A of OAR 340-052.)
In addition, new sewer pipes must be thoroughly flushed and inspected by video, after trench backfilling is complete and prior to city acceptance. This includes video confirmation that the line is free from sags, irregular joints and connections, obstructions, restrictions or other anomalies that may cause solids to accumulate.
Pump station inspection and testing shall be performed to manufacturer’s specifications in the presence of public works personnel or designated representative. Testing documentation must be provided to public works for approval prior to city acceptance. [Ord. 479 § 1 (EDS § 4.7), 2016].