Permanent Stormwater Control Measure Permits
Permanent stormwater control measures (PSCMs) are long-term structures or treatment devices that prevent or reduce the pollution from stormwater prior to discharging to our natural waterways like the St. Vrain Creek. Common PSCMs are Extended Detention Basins, Rain Gardens, Porous Landscape Detention, Sand Filters, Grass Buffers or Swales, and Manufactured Treatment Devices (MTDs). PSCM facilities are managed through three phases, Design Construction, and Operation.
All new developments or re-developments that are larger than one acre require PSCMs. PSCMs are engineered facilities that are designed to remove pollutants from urban stormwater. PSCs must be designed to meet the design standards outlined in Title 14.26. The City has adopted the Urban Storm Drainage Criteria Manual, Volume 3 as the design standards for all PSCM facilities.
Construction of PSCMs is monitored by the City through the Stormwater Construction Activity Permit. PSCMs are inspected during construction by City staff to ensure PSCMs are constructed according to the design plans. PSCMs must also be certified by a professional engineer, and the certification must be submitted to the Stormwater Quality Program. Certification letter templates are available below.
Professional engineers draft certification letters to verify that the PSCM will function according to the design intent. Certification letters include a description of the constructed PSCM, updated calculations for the PSCM, and as-built construction drawings, and updated operation and maintenance manual.
The following certification letter templates are available:
- Detention Only Certification Letter Template
- Extended Detention Basin & Detention Certification Template
- Extended Detention Basin Certification Template
- Grass Swale Buffer Certification Template
- Hydrodynamic Separator Certification Template
- Rain Garden & Detention Certification Template
- Rain Garden (Fully Infiltrating) Certification Template
- Rain Garden Certification Template
- Sand filter & Detention Certification Template
- Sand Filter Certification Template
For detention or water quality facilities that require major sediment removal as a non-routine maintenance activity, recertification of the storage volume is required once the maintenance activity is complete. To recertify storage volume of a previously constructed facility please use the following template letter:
After construction, PSCMs must be regularly inspected and maintained to ensure that they continue to operate. The City issues a PSCM permit for all private PSCMs that are constructed in the City. The permit is issued to the owner of the PSCM and includes requirements that the facility is maintained, inspected at least once annually, and an annual report must be submitted to the City. The permit also requires that contact information for the PSCM owner is kept up to date. The PSCM Permit Application, as well as the Annual Report is provided below. Additional information including general facility descriptions, inspection report templates, and standard operation and maintenance frequencies is provided for each PSCM type.
In accordance with the terms and conditions of the PSCM Permit, all permittees are required to conduct and document at least one inspection annually for each PSCM facility and submit the completed inspection to the Stormwater Quality Program. The City of Longmont has developed standardized inspection forms that address all required inspection elements for each PSCM type.
Beginning in 2026, completed owner inspection forms must be submitted by October 31. A separate inspection form is required for each individual facility. If you have any questions regarding the inspection forms or the inspection process, please contact the Stormwater Quality Program.
- Extended Detention Basin (EDB) Inspection Form
- Rain Garden (RG) Inspection Form
- Sand Filter (SF) Inspection Form
- Grass Swale (GS) Inspection Form
- Grass Buffer (GB) Inspection Form
- Porous Landscape Detention (PLD) Inspection Form
- Hydrodynamic Separators, Underground Detention, or other Manufactured Treatment Devices (MTDs) Inspection Form
