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Stormwater Quality and NPDES 
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The National Pollutant Discharge Elimination System (NPDES) Stormwater Program regulates stormwater discharges from three potential sources: municipal separate storm sewer systems (MS4s), construction activities, and industrial activities. Most stormwater discharges are considered point sources, and operators of these sources may be required to receive an NPDES permit before they can discharge. This permitting mechanism is designed to prevent stormwater runoff from washing harmful pollutants into local surface waters such as streams, rivers, or lakes.

In compliance with the provisions of the Colorado Water Quality Control Act and the Federal Water Pollution Control Act; the City of Thornton is required to obtain a permit from the Colorado Department of Public Health and Environment which authorizes the City to discharge stormwater associated with a Municipal Separate Storm Sewer Systems (MS4). Such discharges are allowed in accordance with the conditions of this MS4 Permit.

 In accordance with the permit requirements the City of Thornton developed, implemented and enforces a Stormwater Management Program designed to reduce the discharge of pollutants to the maximum extent possible to protect water quality.


The MS4 Permit and the Stormwater Management Program require the City of Thornton to implement six minimum control measures over the next permitted period of 2008 – 2013. These minimum control measures are as follows...


Public Education and Outreach

MS4s are required to educate their community on the pollution potential of common activities, and increase awareness of the direct links between land activities, rainfall-runoff, storm drains, and their local water resources. Most importantly the requirement is to give the public clear guidance on steps and specific actions that they can take to reduce their stormwater pollution-potential.

Public Participation and Involvement

MS4s are required to follow all State, and local public notice requirements when implementing their stormwater program.

Illicit Discharge Detention and Elimination

Illicit discharges are generally any discharge into a storm drain system this is not composed entirely of stormwater. The exceptions include discharges from emergency fire fighting activities and discharges specifically authorized by a separate permit.

Construction Site Runoff Control

Stormwater runoff from construction activities can have a significant impact on water quality. As stormwater flows over a construction site, it picks up pollutants like sediment, construction debris, and chemicals such as gas, fertilizer, and paint. Polluted stormwater runoff can harm or kill fish and other wildlife. Sedimentation can destroy aquatic habitat and high volumes of runoff can cause stream bank erosion.

Post Construction Site Runoff Control

MS4s are required to address post-construction stormwater runoff from new development and redevelopments that disturb one or more acres. This primarily includes developing strategies to implement a combination of structural and non-structural BMPs, an ordinance to address post-construction runoff, and a program to ensure adequate long-term operation and maintenance of Best Management Practices (BMPs).

Pollution Prevention / Good Housekeeping

MS4s are required to develop and implement an operation and maintenance program with the ultimate goal of preventing or reducing pollutant runoff from municipal operations into the storm sewer system. The program includes employee training on how to incorporate pollution prevention/good housekeeping techniques into municipal operations such as parks and open space maintenance, fleet and building maintenance, new construction and land disturbances, and stormwater system maintenance.

 

Keep Thornton waters clean button


City of Thornton
9500 Civic Center Drive, Thornton, CO 80229
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