Sanitary and Combined Sewers
In general, requirements for sanitary and combined sewer mains are as described above for storm drain pipes with the following differences:
- All sewer pipe must be designed and constructed to give mean velocities, when flowing full, of not less than 3 fps.
- Minimum pipe diameter is 6 inches for a side sewer, 8 inches for a mainline sanitary sewer and 12 inches for a mainline combined sewer.
- Manholes are required every 350 feet.
- Minimum pipe depth is 12 feet.
Side Sewers and Service Drains
The pipeline between the building and the sewer or storm drain main is a side sewer or service drain, respectively. All side sewer and service drain work within the right-of-way requires a Street Use Utility Permit issued by SDCI on behalf of SDOT. Additional information is available in Seattle Municipal Code: Chapter 21.16 Side Sewer Code, SDCI DR 4-2011/SPU DR 2011-004 Requirements for Design & Construction of Side Sewers (Drainage & Wastewater Discharges) (2011) and SDCI CAM 503: Side Sewer Permits in Seattle (2012).
Minimum Grade, Pipe Size and Materials, Connection Details, Installation and Testing Requirements
Side sewers and service drains shall be designed and installed in accordance with the SDCI DR 4-2011/SPU DR 2011-004 Requirements for Design & Construction of Side Sewers (Drainage & Wastewater Discharges) (2011) and City of Seattle Standard Specifications and Plans (2014). New core taps shall be per SPU Core Tap Procedures (2010).
Side sewers and service drains are owned and maintained by the property owner. The minimum grade is 2%. Ownership of side sewers shall be according to the Seattle Municipal Code: Chapter 21.16.190 – Ownership of side sewers.
Use of Existing Side Sewers
It is possible to use existing side sewers in lieu of a new connection in some cases. See the Seattle Municipal Code: 21.16.240 – Use of existing side sewer for more details.
For build-overs for SPU owned sewer and drainage appurtenances, the applicant shall follow the guidance SDCI Tip 507: Build-Over and/or Re-Route Review and Approval Process (2015).