Prohibited Discharges and Exemptions

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Prohibited Discharges to the Storm Drainage System

Storm drains discharges directly to the river without treatment and are designed to accept rain water and snow melt.  Certain discharges are prohibited and are listed in section 14.26.050 of the Longmont Municipal Code:


It is illegal for a person to discharge or cause to be discharged anything that would cause pollution of the waters in the Municipal Separate Storm Sewer System (MS4) or receiving water including, but not limited to, discharges that:

1. Cause or contribute to violations of any applicable water quality standard;

2. Cause or contribute to any blockages of or damage to the MS4;

3 Constitute a fire or explosion hazard;

4. Contain any toxic or hazardous material including, but not limited to, pathogens, chemicals and automotive fluids and hazardous waste as defined in 40 CFR 261.3;

5. Have a pH less than 6.5 standard units or greater than 9.0 standard units;

6. Cause or contribute to a public nuisance as defined in Chapter 9.04 of the Longmont Municipal Code;

7. Contain radioactive material;

8. Result from any construction activities including, but not limited to, earthwork, paving, concrete placement, painting, sawcutting, and material storage;

9. Consist of trucked or hauled wastes including, but not limited to, septage, recreational vehicle waste, and water from mobile washing operations, (mobile pet washing operations); or

10. Contain or consist of any material that is harmful to humans, animals, aquatic life or the environment including, but not limited to trash, refuse, rubbish, garbage, food wastes; pet wastes; litter; other discarded or abandoned objects, floatables, cleaning products; landscaping materials, lawn clippings, leaves, branches or other landscaping and yard debris; wastes and residues from mobile washing operations; discharges from toilets, sinks, industrial processes, cooling systems, boilers, fabric cleaning, equipment cleaning and commercial vehicle cleaning; motor oil, antifreeze and substances added to the storm drain to control root growth.


The following discharges to the MS4 are exempt from the discharge prohibitions established by this chapter unless the discharge either by itself or in combination with other discharges, unduly restricts the capacity of the MS4 to carry design storm flows:

1. Line flushing, tank draining or other potable water sources when managed in accordance with the requirements of a CDPHE treated water discharge permit or other applicable BMPs;

2. Irrigation return flows, diverted stream flows, natural riparian habitat or wet-land flows, rising ground water and natural springs;

3 Uncontaminated ground water infiltration to storm drains;

4. Uncontaminated pumped ground water from foundation or footing drains or crawl space pumps, provided such water does not flow onto sidewalks, or cause nuisance or public safety conditions such as algae growth, ice formation or sediment buildup in gutters or surfaces;

5. Air conditioning condensation;

6. Water from individual residential car washing;

7. Discharges from swimming pools, spas and hot tubs if the discharges contain no detectable residual chlorine,

8 Discharges necessary to protect public health and safety, such as flows from firefighting;

9. Dye testing, provided that the testing and materials to be used have been approved by the applicable federal, state or local regulatory agencies and that the person(s) doing the testing provide verbal notification to said agencies a minimum of twenty-four hours prior to the time of the test;

10. Runoff of roadway anti-icing and deicing agents and street wash water, provided that best management practices to reduce or prevent pollution are followed;

11. Discharges from activities related to management or operation of agricultural land;

12. Discharges resulting from the maintenance and repair of any facilities, including structures, pipes, ditches, etc., performed by the City of Longmont, provided that the maintenance and repair are necessary to maintain the integrity of the MS4 or protect the health, safety or well-being of the public, city personnel and the environment and that BMPs are utilized to manage the discharges to the extent possible; or

13. Any other water source not containing pollutants,

The prohibitions set forth in this section shall not apply to any non-storm water discharge permitted under an NPDES permit, waiver or waste discharge order issued and administered under the authority of the federal Environmental Protection Agency (EPA) or the CDPHE under the authority of the EPA, provided that the discharger is in full compliance with all requirements of the permit, waiver or order and other applicable laws and regulations, and provided that written approval has been granted by the city for any discharge to the storm drain system.

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