How Do MHLD Sewer Services Differ?
An MHLD is a type of land division that allows specified housing types to be divided into separate lots through an expedited process. MHLDs differ from standard land divisions in some key ways. To accommodate these differences, Environmental Services developed a sewer route-of-service policy unique to MHLDs. Environmental Services allows two unique sewer connection configurations specifically for MHLDs: 1) wye laterals, and 2) MHLD shared sewers.
For a complete description of MHLDs, review procedures, submittal requirements, and information about other utilities, see the Middle Housing Land Divisions webpage.
Please note that the information provided on this page applies to MHLD developments only.
What Is a Wye Lateral?
A wye lateral is when two individual building sewer laterals from the MHLD development join at a single wye fitting before connecting to the public sewer main. MHLD wye laterals must abide by the following:
- Wye laterals must be installed per the double sanitary detail shown in the graphic and follow Portland details and drawings P-262, P-257 and ENB- 4.17. A cleanout must be installed on each lateral upstream of the wye-fitting.
- Each wye lateral can serve a maximum of two units.
- A minimum 6-inch lateral between the sewer main and the wye-fitting is required. Pipe sizing and acceptable materials are detailed under ENB 4.17 for laterals in the public right-of-way.
What Is an MHLD Shared Sewer?
MHLD shared sewers consist of a single sanitary lateral connection to the public main, with the private sewer system on the property shared by the owners of the lots that the system serves. MHLD shared sewers must abide by the following:
- The portion of the MHLD shared sewer system on private property must meet the requirements of the Bureau of Development Services and may require a plumbing code appeal.
- MHLD shared sewers require private easements and maintenance agreements for Environmental Services to consider them conforming sewers per Title 17.32. Easements and agreements are managed and reviewed by the Bureau of Development Services.
- Property owners are responsible for maintaining the shared system on private property.
- When an MHLD shared sewer is proposed, all MHLD lots should use that sewer unless infeasible or impractical due to technical constraints.
- A minimum 6-inch lateral within the right-of-way is required and must follow the standard details and drawing P-262 as well as ENB 4.17.
Route-of-Service Options for MHLDs With Four or Fewer Units
The following route-of-service options are acceptable for MHLDs with four or fewer units:
- Individual sewer laterals that do not cross another parcel and connect to the public sewer system within each parcel's frontage.
- Individual sewer laterals that cross one or more parcels within the MHLD parent parcel, within private easements approved by the Bureau of Development Services.
- Individual sewer laterals that wye together with no more than one other lateral from the same MHLD development, according to Environmental Services standard wye configuration graphic.
Route-of-Service Options for MHLDs With Five or More Units
The following route-of-service options are acceptable for MHLDs with five or more units.
- Any of the sewer lateral configurations approvable for four or fewer units.
- An MHLD shared sewer with one lateral to the public main, provided easements and maintenance agreements are recorded over it and it meets the requirements of the Bureau of Development Services Plumbing Department. Note that a plumbing code appeal may be required.
Alternatives for Unique or Challenging Scenarios
The City may allow or require the use of MHLD shared sewers for other MHLD development applications, including for applications with four or fewer parcels, when Environmental Services determines that the provision of sewer service through an MHLD shared sewer is preferable due to concerns for human health and safety, environmental impacts, construction complexity, right-of-way conflicts or other technical factors. MHLD shared sewers are only allowed with adequate easements and maintenance agreements in place. Example scenarios may include:
- Proximity to or conflict with water lines.
- Presence of vaults, franchise utilities, or other features that, in aggregate, make individual or wye connections infeasible.
- Construction of a public sewer main extension in the public right-of-way to provide individual or wye connections is not the preferred solution, as determined by Environmental Services.
- The depth, age, material, or condition of the public sewer main makes multiple connections an unacceptable risk to Environmental Services.
Other Considerations
Depending on the location and availability of existing Environmental Services sewer infrastructure relative to the MHLD proposal, route-of-service rules may still require an extension of the public sewer in the existing right-of-way under a public works permit to bring the public sewer to a point that allows the MHLD to connect to the City's system.
One or more sewer laterals may be allowed to cross neighboring properties outside of the parent parcel in private easements, subject to ENB-4.07 Section 6.A.3.