Work through the following steps to determine the options available for meeting SWMM requirements for your project.
Step 1: Determine if your project area discharges to and existing facility in the right-of-way
- Identify any existing stormwater facilities within the vicinity of the project site.
- If existing sumps or other facilities are present, coordinate with PP&D Environmental Services Development Engineering staff (hotline number 503-823-7761, option 3) to determine if an existing facility is adequate to meet SWMM requirements for the triggered impervious area.
- Upgrades of modifications may be required if the facility is not adequate to meet SWMM requirements. Adequacy will depend on conveyance to the facility, capacity, condition and configuration. For sumps, an existing facility will not be sufficient as is if a sedimentation maintenance hole is not present.
- If modifications are necessary, they will be reviewed through the Public Works Permit application.
Step 2: Determine if your project automatically qualifies to pay an offsite stormwater management fee (Staff Review Special Circumstances)
Projects in the right-of-way can meet SWMM requirements by automatically paying the offsite management fee for all or part of their project when they meet the criteria for Staff Review Special Circumstances (see SWMM Section 1.7.1). The offsite stormwater management fee will be allowed for the qualifying impervious areas. To determine if all or a portion of your project qualifies, answer the following questions:
- Does the project propose improvements to meet ADA requirements, or create, expand, or replace pedestrian facilities in the right-of-way outside of travel and parking lanes (e.g., sidewalks, shoulder widening)?
- Does the project construct right-of way improvements, through a public works permit, with less than 120 ft. of frontage per block face?
- Does the project have incidental areas that total 500 ft2 or less that cannot be managed?
- Yes. Improvements qualify for Staff Review Special Circumstances fee. Please complete the Staff Review Special Circumstances Application Form and submit it along with your permit documents. A full list of Staff Review Special Circumstances qualifications are found in the SWMM Section 1.7.1. No application fee is required for a Staff Review Special Circumstances. Include the tree credit worksheet from Step 3 below if the project has street trees, this will reduce the fee.
- No. Improvements do not qualify for Staff Review Special Circumstances fee payment. Follow normal SWMM process for all triggered impervious area or apply for a Committee Review Special Circumstances.
Additional eligibility may apply if the project constructs right-of-way improvements in a combined sewer system and a sed-sump system is not feasible, or a lined facility is required. Please contact PP&D Environmental Services staff at 503-823-7761.
Additional notes on the Staff Review Special Circumstances: For sites with existing facilities, payment of the offsite stormwater management fee is not necessary if the existing facility is adequate per permit staff. This is typically true in the sumped areas of Portland.
Step 3: Apply Tree Credits
- Trees in the right-of-way can be used to provide stormwater management for some impervious surfaces, subject to the design criteria in SWMM Section 6.2.5.
- Tree credits can only be applied to triggered impervious areas located on the same side of the street as the tree itself.
- Submit the Tree Credit Worksheet with the Public Works Permit.
Step 4: Construct New Stormwater Facilities
The type of new stormwater facility will depend on the site evaluation criteria described in SWMM Section 2.2. Refer to SWMM Chapter 6 for public stormwater facilities design criteria and submittal requirements.
- Stormwater Facilities and Right-of-Way Dedication: Additional right-of-way dedication for stormwater facilities is not required for most development projects. Additional right-of-way dedication for stormwater facilities will only be required for projects that build new streets within new rights-of-way (for example, large subdivisions or site master plans) when the dedication is needed to meet SWMM requirements. The type, size and placement of required stormwater facilities will impact necessary right-of-way dedication widths.
- Calculating Facility Basin Areas for Sizing: The drainage basin area for sizing a facility will vary depending on the specific type of stormwater facility proposed.
- Sumps: Sumps must be sized for the full contributing drainage area, not just the new impervious surface area.
- Vegetated Stormwater Facilities: These must be sized based on the total triggering area. For most projects, this will consist of the new or redeveloped impervious area alone, but some projects will also trigger the SWMM because of a New Connection or Route of Conveyance (Section 1.2.2). For the latter, the relevant area is the existing impervious area that sheet flows directly to the new curb subject to the new connection criteria described above (for public works permitted projects, upstream gutter flow from outside of the project frontage can be excluded).
- Vegetated infiltration facilities are required to include the new impervious area, plus the half street associated with the development.
- For other facility types, discuss drainage basin delineation with the assigned City reviewer.
Step 5: Apply to get approval to pay the offsite stormwater management fee (Committee Review Special Circumstances)
A Committee Review Special Circumstances request must demonstrate why it is technically infeasible to manage stormwater runoff for the area not being managed. Typically, site constraints related to grading, slopes, or topography are the most common reasons construction of a stormwater facility would be infeasible. Refer to SWMM Section 1.7.2 for additional information.
To determine if this option is appropriate for your project, ask yourself this question: Is it technically infeasible to meet SWMM requirements for all or a portion of improvements in the right-of-way (consult with PP&D reviewer as applicable)?
- No. Follow normal SWMM process for all triggered impervious area.
- Yes. Apply for Committee Review Special Circumstances. Committee Review Special Circumstances require payment of the application fee for all applications, and the offsite fee, if approved.
If the application is denied, follow normal SWMM process for all triggered impervious area.
If the application is approved, pay offsite stormwater management fee for approved areas.
Always consult the current SWMM for complete requirements.