Environmental Rules in Longmont, CO (2026)
4 verified environmental rules for Longmont, Colorado, sourced directly from the municipal code and official government pages.
Verified from official government sources
Stormwater Management
Longmont's stormwater program is governed by LMC Chapter 14.26 (Stormwater Quality) and the city's NPDES MS4 permit issued by the Colorado Department of Public Health and Environment. Any development disturbing more than one acre — or that is part of a larger common plan of development — must design, construct, and permanently maintain on-site Permanent Stormwater Control (PSC) measures to keep pollutants out of the St. Vrain Creek watershed. Permits are administered by Environmental Services and reviewed in three phases (Design, Construction, Operations & Maintenance), with annual maintenance reports required for the life of the development.
Stormwater Quality in Longmont
Heavy RestrictionsErosion Control
All construction sites in Longmont must install and maintain erosion and sediment control BMPs to keep soil out of the MS4 and the St. Vrain Creek system. Authority comes from LMC Chapter 14.26 (Stormwater Quality) and is implemented through the 2025 Longmont Design Standards. Sites disturbing one acre or more also need the State CDPS Stormwater Construction Permit through CDPHE. The building permittee is responsible for erosion control associated with any building permit, regardless of acreage.
Erosion Control in Longmont
Heavy RestrictionsFlood Zones
Longmont's floodplain regulations are codified in LMC Title 20 (Floodplain Regulations). St. Vrain Creek runs through the heart of the city and produced the catastrophic September 2013 flood that displaced hundreds of residents — making floodplain compliance one of the most active regulatory areas in town. Any construction or development inside a FEMA Special Flood Hazard Area (SFHA) requires a Floodplain Development Permit issued by the city Floodplain Administrator, with a $100 application fee.
Flood Zones in Longmont
Heavy RestrictionsGrading & Drainage
Longmont reviews grading and drainage through the Land Development Code (Title 15) plus the city's published Design Standards. Drainage Studies are required as part of the Design Review process for new development, and stormwater conveyance must be sized to safely pass the 100-year event without aggravating off-site flooding. Permanent Stormwater Controls under LMC Chapter 14.26 stack on top of the drainage requirements for any site disturbing one acre or more.
Grading and Drainage in Longmont
Heavy RestrictionsLooking for Boulder County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Longmont city rules.
Environmental Rules in Boulder County →