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Stormwater Quality

General Permit for Stormwater Discharges Associated with Municipal Separate Storm Sewer Systems
(CDPS-MS4 General Permit)

Contact:   Traci Shambo    498-5701   Send E-mail

Larimer County has a long history of protecting our natural resources, including stormwater. When dealing with stormwater issues, as a land developer or an individual homeowner, stormwater should be viewed as a valued resource - not a liability. When thought of in this light, it makes sense to protect the quality of that resource from pollution. We remain committed to being good stewards of our water resources. Not because it is required - it's the right thing to do!

In 2003, under provisions of the Colorado Water Quality Control Act and the Federal Water Pollution Control Act, Larimer County was designated by the Water Quality Division of the State Health Department as a Phase II Municipal Separate Storm Sewer System (MS4) Community. With this designation, Larimer County was required to apply for the Colorado Discharge Permit System (CDPS) General Permit for Stormwater Discharges Associated with MS4s. Under the regulation of this permit, Larimer County is required to have a Stormwater Quality Management Plan that has the goal to protect stormwater quality by controlling and/or eliminating pollutant discharges into stormwater sewer systems.

The regulation requires Larimer County to administer a group of programs to assure water quality is maintained. It also requires any individual or entity, planning construction activities that involve disturbance of one acre or greater, to design and implement erosion control and water quality measures into such activities and obtain a stormwater permit from the Colorado Department of Public Health and Environment (CDPHE).

Following are links to information regarding regulatory requirements as well as general water quality information. They provide useful information for land development issues as well as knowledge of water quality issues.

Stormwater Management Plans Required

Regulations require a permit be obtained from the Colorado Department of Public Health and Environment (CDPHE) for construction activities which disturb an area of 1 acre or larger.  (More information)

Larimer County Stormwater Quality Management Plan

The current Colorado Discharge Permit System (CDPS) General Permit for Stormwater Discharges Associated with MS4s (COR0900) became effective July of 2016 and will expire June of 2021. The MS4 permit regulations for Larimer County are now effective within specific urbanized areas as shown on the current Larimer County MS4 Permit Coverage Areas Map. Under the terms of the current MS4 permit, effective July 2016, Larimer County is required to implement our County Stormwater Management Plan in accordance with the previous permit terms until the new Stormwater Management Plan is implemented in accordance with the compliance schedule of the current MS4 permit.

Illicit Discharge Detection & Elimination

Larimer County has a Stormwater Quality Ordinance that addresses illicit discharges into the stormwater system. The ordinance is a required enforcement mechanism to comply with the National Pollutant Discharge Elimination System program, and addresses recurring offenses of prohibited discharges into the stormwater system. The links below provide additional information about the ordinance, as well as other public information provided to citizens throughout the Fall of 2007 related to stormwater quality.

Open House Presentation     Frequently Asked Questions     Stormwater Quality Survey

Keep It Clean

Larimer County has joined the "Keep It Clean" Campaign, an educational outreach effort to enhance water quality.

Additional Information

Engineers and Developers



Business and Industrial

Industrial Stormwater


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