National Pollutant Discharge Elimination System (NPDES)

Municipal Separate Storm Sewer System

Polluted storm water runoff is often transported to municipal separate storm sewer systems (MS4s) and ultimately discharged into local rivers and streams without treatment. The EPA's Stormwater Phase II Rule establishes an MS4 stormwater management program that is intended to improve the Nation's waterways by reducing the quantity of pollutants that stormwater picks up and carries into storm sewer systems during storm events.

Common pollutants include oil and grease from roadways, pesticides from lawns, sediment from construction sites, and carelessly discarded trash, such as cigarette butts, paper wrappers, and plastic bottles. When deposited into nearby waterways through MS4 discharges, these pollutants can impair the waterways, thereby discouraging recreational use of the resource, contaminating drinking water supplies and interfering with the habitat for fish, other aquatic organisms and wildlife.

In 1990, the EPA promulgated rules establishing Phase I of the National Pollutant Discharge Elimination System (NPDES) stormwater program. The Phase I program requires operators of "medium" and "large" MS4s, that is, those that generally serve populations of 100,000 or greater, to implement a stormwater management program as a means to control polluted discharges from these MS4s. The Stormwater Phase II Rule extends coverage of the NPDES stormwater program to certain "small" MS4s like Niles, but takes a slightly different approach as to how the stormwater management program is developed and implemented.

This web page includes links to the documents that are part of the Village of Niles' efforts to minimize pollution from stormwater runoff as part of its federal National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) Phase II permit.


Niles - NPDES MS4 Permit
Niles - NPDES Notice of Intent
Niles - 2015/2016 MS4 Annual Report
Niles - 2014/2015 MS4 Annual Report
Niles - 2013/2014 MS4 Annual Report
Niles - Storm Water Management Plan

Additional Information

A full explanation of the NPDES MS4 program can be found at the USEPA website and the IEPA website.

Combined Sewer Overflows

Most older cities in the United States were built with combined sewer systems. This means the sewer system was designed to collect rainwater runoff, domestic sewage and industrial wastewater all in a single pipe.

Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant where it is treated and then discharged to a water body. However, during periods of heavy rainfall or snowmelt, the runoff volume can exceed the capacity of the sewer system or treatment plant, resulting in the discharge of excess wastewater directly to nearby streams, rivers or other water bodies.

The long term plan for the region to reduce and/or eliminate direct discharges of wastewater is called the Tunnel and Reservoir Plan (TARP), sometimes referred to as the Deep Tunnel. The TARP consists of a series of tunnels and reservoirs to temporarily store excess runoff during rain events so it can be treated before discharge into the waterways. In addition, the Village of Niles continues to construct separate storm sewers as part of street reconstruction projects to reduce the volume of rainwater that flows into the combined sewer system.

Metropolitan Water Reclamation District

The Metropolitan Water Reclamation District (MWRD) has flow monitoring equipment installed at 30 CSO outfalls along the north branch of the Chicago River, including the 10 Village of Niles outfalls. In addition, the MWRD has created a public notification plan that includes signage at the outfalls, a web page to inform the public of CSO occurrences, and an email address book of interested parties.

Village Requirements

In the interest of avoiding a redundancy of efforts, the MWRD has invited TARP (Tunnel and Reservoir Plan) municipalities to use the MWRD Public Notification Plan for their public notification compliance. Given that all of the village’s outfalls are currently monitored by the MWRD, the village proposes that the MWRD’s public notification program largely meets the village’s requirements. To complement the MWRD’s program, the Village of Niles to:
  • Provides a link from the Village of Niles website to the MWRD CSO.
  • Installed signage, adhering to the MWRD developed specifications, at the village-maintained outfalls.
  • Coordinated with the MWRD regarding the flow monitoring data such that the village will be aware of any combined sewer overflows.

Emergency Operation Plan

The Director of Public Services shall at all times keep the Mayor, and/or his appointee, informed of any dangerous condition that may exist. Should the village administration consider the condition to be an emergency, then the village's Emergency Operation Plan shall be implemented.

This program was developed in compliance with the requirements of the village’s National Pollutant Discharge Elimination System (NPDES). The Combined Sewer Overflow (CSO) program was established June 1, 2003. CSO General Permit Number: ILM580035


Niles - CSO Application
Niles - Operational and Maintenance Program
Niles - Pollution Prevention Program
Niles - Public Notification Plan
Niles - CSO Outfall Map