Step 1: Determine if the right-of-way activities are exempt.
For additional detail see the SWMM Section 1.2.1.2.
If your project involves only one the following activities in the right-of-way, then you do not need to continue through the following steps.
- Right-of-way work that can be completed under a PBOT Minor Improvement Permit.
- Construction of curb ramps that do not project into the street beyond existing curb lines.
- Redevelopment of pedestrian-only areas when the pavement material remains the same.
- Pavement restoration for utility trenching work.
- Base repair of a public street when no more than 50% of the street is repaved.
Step 2: Calculate new or redeveloped impervious area in the right-of-way.
See SWMM Section 1.2.1 for additional information.
Calculate new and redeveloped impervious areas in the right-of-way:
New development and redevelopment activities that create or replace 1000 square feet or more of impervious area are subject to the requirements of the SWMM unless specifically exempt. Triggered impervious area must be based on all constructed or replaced area that is not exempt. It is not calculated based on net change in impervious area. Common scenarios include:
- Full-width roadway replacement with base repair.
- Construction of a new sidewalk behind an existing curb.
- Full-width alleyway pavement improvements with base repair.
Subtract exempt impervious areas in the right-of-way:
Refer to SWMM Section 1.2.1.2 for a complete list of pavement exemptions.
- Pavement surface maintenance: This includes repaving and resurfacing within the existing footprint of the paved surface, provided no subgrade (soil) is exposed and pavement is replaced in-kind such as using the same paving material.
- Replacement of pedestrian-only areas: Replacement in-kind of pedestrian-only areas (including sidewalks).
Construction of curb ramps: Adding a curb ramp or replacing an existing curb ramp when the proposed curb is not constructed into the street beyond the existing curb line.
Reducing the radius of a corner curb ramp so the new curbline remains within the extension of the existing curblines is exempt.
Examples of improvements and the resulting impervious areas triggering SWMM requirements:
Step 3: Add areas of new connection or new route of conveyance in the right-of-way.
See SWMM Section 1.2.2 for additional information.
Projects that make new connections, route new drainage areas to a stormwater receiving system, or change an existing connection or discharge point must provide stormwater management for those areas if the project connects or reroutes impervious areas that are 1000 square feet or more in total. This applies when the project involves any of the following:
- Changing the hierarchy level: Rerouting impervious area from one storm system to another, e.g., combined system to the separated system (see SWMM 1.3.4 for hierarchy levels).
- Changing to a public discharge point: Rerouting impervious area from an existing private discharge to a public discharge point.
- Formalizing an existing drainage or conveyance system: Installing new infrastructure to convey stormwater runoff from impervious areas within the project boundary (e.g., constructing curb and gutter on an uncurbed street, installing a new stormwater outfall, converting open-channel conveyance to piped conveyance). For public works permit projects, the subject area will be considered the area within the frontage of the development project or the area of new or redevelopment impervious area, whichever is larger.
Step 4: Does the sum of steps 2 and 3 exceed 1000 square feet?
No. If your project area is less than 1000 square feet, then your project does not trigger SWMM requirements. You are done.
Yes. If your project area is 1000 square feet or greater your project triggers the SWMM and requires stormwater management. Learn more about how to meet SWMM requirements.