Evanston’s Innovative Sewer Improvement Program

The entire City of Evanston was previously served only by a combined sewer system, a system that carries both sanitary waste from homes and businesses and storm water. As long ago as 1902, the City’s combined sewer system was declared by the Commissioner of Public Works to be “inadequate in size and depth to serve the demands of the city.” Sewage water backing up into basements was a common event during any significant rain event. Over time, increased amounts of impervious surfaces, such as paved alleys and parking lots exacerbated the flooding.

In 1990 the City Council approved a Long Range Sewer Improvement Program to mitigate property damage caused by sewage backing up into basements. The program consisted of the following components.

1. The installation of larger diameter relief combined sewers at a depth that could convey storm water and overflows from the combined sewer system to the Metropolitan Water Reclamation District (MWRD) deep tunnel beneath the North Shore Channel.
2. The installation of flow restrictors in alley and street drainage inlets connected to the combined sewer system. These prevent the combined sewer from becoming overloaded during moderate and extreme rainfall events including, but not limited to the 100 year design storm. This provides basement backup protection under nearly all situations. The storm water that is forced to stay on the street due to the inlet restrictors can flow down the street for up to two blocks where it is intercepted by high capacity inlets that flow directly into the relief sewer system.
3. In a few areas separate storm sewers were installed to convey surface drainage directly to the North Shore Channel.

This innovative approach of partial sewer separation combined with overland street flow control was utilized because it was much more cost effective than installing a completely new separate storm sewer system throughout the entire city.

The Long Range Sewer Improvement Program was constructed between 1991 and 2008 and cost approximately $210 million to complete. The City received the Clean Water State Revolving Fund 2006 Pisces Award for innovative use of Clean Water Act State Revolving Fund (SRF) funding to improve water quality. In 2009, the City received the Illinois Section – American Society of Civil Engineers Outstanding Civil Engineering Achievement of the Year Award for the Combined Sewer Relief Program.

In the Event of a Sewer Emergency

Between the hours of 7 a.m. and 7 p.m. dial 311 (847-448-4311 outside the city) and state the nature of the emergency. If the emergency occurs after 7 p.m., call the Utilities Department after-hours emergency number at 847-475-6880. An employee will be dispatched to analyze the cause of the problem as soon as possible.

Do not use toilets and sinks unless absolutely necessary, as water sent down your drain will end up adding to the problem.

Sewage Backup and Flooding

There are two different types of basement flooding.

1. If the water in the basement is clear, this indicates that storm water has entered the basement through window wells or doors, that storm water has seeped into the basement through cracks in the basement walls or floor, or that a sump pump has failed. These types of issues cannot be resolved by the City. However, they should be reported so the City can take appropriate action if warranted.
2. If the water in the basement is discolored and has an odor, this indicates that sewage water has backed-up or entered the basement through floor drains, sump pumps, toilets or laundry sinks. Please contact the City via 311 if you suspect the water entering your basement is sewage water. An investigation will be conducted to determine if the City sewer has contributed to your problem.

Causes of Sewage Backups:

1. The City’s combined sewer system has become overwhelmed by excessive rainfall.
   • More storm water has entered the combined sewer system than it can handle, causing water to back-up into basements. Unfortunately there isn’t anything that can be done to relieve this type of flooding until after the rain event subsides and sewer flow returns to normal.
2. Blockage in the City sewer.
   • Debris, roots, or a sewer collapse blocks or hinders the flow of the sewage in the City’s combined sewer system. The City’s Sewer Division will take corrective action to eliminate the problem so that normal flow can be re-established.
3. Blockage in the property owner's private sewer lateral.
   • Debris, roots, or a sewer collapse blocks or hinders the flow of sewage in the property owner’s sewer lateral, or the sewer lateral becomes overwhelmed by storm water.
   • The property owner will need to contact a plumber to clear the blockage or repair a collapsed pipe in the sewer lateral. We recommend that the homeowner seek three quotes from licensed plumbers for any type of sewer work. Property owners are welcome to contact the Utilities Department via 311 to review the plumber’s recommendations, but ultimately the property owner must make the decision on how to proceed.
   • Frequently, private sewer back-ups are a result of the sewer lateral becoming overwhelmed by the amount of storm water entering it from roof gutters and downspouts. The Utilities Department highly recommends that all downspouts discharge to the ground rather than being connected to the sewer lateral. Please contact the Utilities Department via 311 to receive guidance on downspout disconnection.

Evanston Sewer History

The Evanston sewer system is comprised of three systems: a combined sewer system, a relief combined sewer system and a storm sewer system. The City does not have a sewage treatment plant. All of Evanston’s sewage flows to the Metropolitan Water Reclamation District (MWRD) system and is treated at the MWRD North Side Water Reclamation Plant at the intersection of McCormick and Howard in Skokie.

The Evanston combined sewer system (see map) was constructed as the city was developed, and the majority of the system is 80 to well over 100 years old. Typical of combined sewer systems built at the time, the sewer conveyed sanitary waste as well as storm water during rain events. Amazingly, over 60 percent of the 144 miles of combined sewers are comprised of 12-inch diameter or smaller pipes. While this size is adequate for sanitary flow, it is not at all suited for storm water drainage. As long ago as 1902, the city’s combined sewer system was declared by the Commissioner of Public Works to be “inadequate in size and depth to serve the demands of the city.”

The majority of the combined sewer system is constructed of vitrified clay tile pipes with the larger diameter pipes constructed of brick or segmental clay tiles. Originally the combined sewer system discharged to Lake Michigan. In 1889 the state legislature enabled the creation of the Sanitary District of Chicago (now called the Metropolitan Water Reclamation District of Greater Chicago) to, among other things, protect the water supply (Lake Michigan) from pollution. The district reversed the flow of the Chicago River and South Branch in 1900, and in 1910 they completed construction of the North Shore Channel. The channel diverted the sewage from the northwestern part of Evanston away from the lake. By 1920 the district had constructed intercepting sewers along Lake Michigan and the Evanston Pumping Station at Elmwood and Lake Streets to divert the sewage from the southern two-thirds of the city to the channel. In 1928 the district completed the installation of an interceptor that follows the channel and carries the sewage to the MWRD North Side Water Reclamation Plant at the intersection of Howard and McCormick in Skokie.

Evanston’s sewer system is greatly dependent on the MWRD sewer system.
During dry weather flow, the combined sewer system flows to the MWRD interceptors and then to the North Side Water Reclamation Plant. During rain events, the sanitary and storm water flow continues to discharge to the MWRD interceptors. However, when the MWRD interceptors become overwhelmed with storm water, the combined sewers begin to discharge to the MWRD deep tunnel system. The deep tunnel is part of the MWRD Tunnel and Reservoir Plan (TARP). Construction of the TARP tunnels began in 1975 and the part that serves Evanston was completed in 1985. In Evanston, the deep tunnel is 22 feet in diameter, approximately 250 feet deep in bed rock and is located directly below the channel. The combined sewers are connected to the deep tunnel by drop shafts that take the flow from the elevation of the combined sewer down to the deep tunnel. Since the McCook Reservoir that will serve Evanston has not been completed, the deep tunnel occasionally begins to fill to its maximum capacity and sluice gates (or valves) are closed preventing any additional flow into the deep tunnel. When this occurs, the combined sewers will begin to discharge to the North Shore Channel. If the channel water level rises too high, the MWRD opens the sluice gates at the Wilmette Pumping Station and the channel begins to discharge to Lake Michigan. To learn more about the MWRD TARP project, visit the MWRD website at www.mwrd.org.

Even after the MWRD deep tunnel was installed, Evanston residents continued to sustain property damage during rain events when the combined sewer system became overwhelmed, forcing sewage to backup into basements. Even though the MWRD had installed a system to handle the combined sewer overflow, Evanston’s sewer system was still too small and shallow to convey storm water to the deep tunnel.

In 1990 the City Council approved a Long Range Sewer Improvement Program to mitigate property damage caused by sewage backing up into basements. The program consisted of the following components.

The installation of larger diameter relief combined sewers at a depth that could convey storm water and overflows from the combined sewer system to the Metropolitan Water Reclamation District (MWRD) deep tunnel beneath the North Shore Channel.
The installation of flow restrictors in alley and street drainage inlets connected to the combined sewer system. These prevent the combined sewer from becoming overloaded during moderate and extreme rainfall events including, but not limited to the 100 year design storm. This provides basement backup protection under nearly all situations. The storm water that is forced to stay on the street due to the inlet restrictors can flow down the street for up to two blocks where it is intercepted by high capacity inlets that flow directly into the relief sewer system.
In a few areas separate storm sewers were installed to convey surface drainage directly to the North Shore Channel.
This innovative approach of partial sewer separation combined with overland street flow control was utilized because it was much more cost effective than installing a completely new separate storm sewer system throughout the entire city.

The Long Range Sewer Improvement Program was constructed between 1991 and 2008 and cost approximately $210 million to complete. The City received the Clean Water State Revolving Fund 2006 Pisces Award for innovative use of Clean Water Act State Revolving Fund (SRF) funding to improve water quality. In 2009, the City received the Illinois Section – American Society of Civil Engineers Outstanding Civil Engineering Achievement of the Year Award for the Combined Sewer Relief Program.

Initially, the relief sewer system was installed prior to the installation of the restrictors. The relief sewer system (see map) consists of 9 miles of shallow tunnels (approximately 60 feet deep) ranging in size from 60 to 120 inches in diameter, and 43 miles of sewer mains ranging in size from 6 to 54 inches in diameter.

On streets where the relief sewers were installed, the system was designed to have storm water drain away without any street flooding during a 5-year storm and have only minimal flooding in isolated areas during a 10-year storm. Street flooding is expected on more significant rain events.

After the relief sewers were installed, the installation of the flow restrictors in the drainage structures still connected to the combined sewer system began. The flow restrictors limit the amount of storm water entering the combined sewer system causing the rain water to stay on the street rather than causing sewage water to backup into basements.

Flow restrictors are located throughout a large portion of the City (see map) and property owners in these areas should expect overland flow and street flooding to occur. Storm water continues to slowly drain away during a rain event and should be entirely gone within two hours after the rain stops

The storm sewer system (see map) discharges directly to the North Shore Channel and Lake Michigan, and it is not connected to the MWRD interceptor sewers or deep tunnel system. The storm sewer system is only utilized during rain events to convey storm water from the street to the channel or the lake. The majority of the storm sewer in southwest Evanston was installed in the late 1970s and early 1980s as part of the City’s Southwest Paving Project. As part of the Long Range Sewer Improvement Program, the storm sewer system in this area was extended east of Asbury Avenue. The storm sewer in the north central and east side of the city was also installed as part of the Long Range Sewer Improvement Program.

Definitions:

Combined Sewer System – a type of sewer system designed to carry both sanitary waste and surface runoff from rain events. During dry weather, Evanston’s combined sewer system discharges to the Metropolitan Water Reclamation District’s interceptor system that flows to the North Side Water Reclamation Plant located at the intersection of Howard Street and McCormick Boulevard in Skokie. During wet weather, the combined sewer system continues to flow to the MWRD interceptor. When the interceptor becomes overwhelmed, the combined sewer system begins to discharge to the MWRD deep tunnel. When the deep tunnel fills, the combined sewer system will discharge to the North Shore Channel.

Relief Combined Sewer System – a type of sewer system designed to carry storm water as well as overflows from the combined sewer system. During dry weather there is generally no flow in the relief sewer system since sewer services are not directly connected to the relief sewer system. Evanston’s relief sewer system discharges to the MWRD deep tunnel system. When the deep tunnel fills, the relief combined sewer system will discharge to the North Shore Channel.

Storm Sewer System – a type of sewer system designed to carry only storm water. Evanston’s storm sewer system discharges to the North Shore Channel and to Lake Michigan.

Drainage Structure – a storm water drain designed to drain rain from paved streets, alleys and parking lots.

Flow Restrictor – a device placed in the outflow pipe of a drainage structure to limit the amount of rain water that flows into the combined sewer system.

Private Sewer Lateral – the sewer pipe installed between the building and the City’s combined sewer system. A private sewer lateral is also referred to as a building sewer or waste tie. In accordance with Title 7, Chapter 13, Section 7, Paragraph (D) of the City Code, the property owner is responsible for the maintenance and repair of the building sewer or lateral including the pipe located in the parkway or street.

Stormwater Best Management Practices – Sometimes referred to as Green Technology, these practices have recently been employed by the City to reduce the amount of storm water that has to be handled by the combined sewer system. Porous pavements have recently been installed in parking lanes along Sheridan Road south of the NU campus. Porous alleys have been installed in south and north Evanston. The effectiveness and durability of these and other practices will be closely monitored to assure their future usefulness and practicality for a sustainable city.

Helpful Hints:

Cleaning Up after a Basement Backup

• Before entering the affected area, assess for potential electrical shock hazards and gas leaks. Gas leaks can occur in hot water tanks and furnaces.
• Wear rubber boots and gloves.
• Wash hands frequently!
• Keep contaminated objects, water, and hands away from mucous membranes (eyes, mouth, and nose).
• Avoid skin contact with sewer water. Be especially careful with cuts and sores. Keep them clean and covered.
• If you receive a cut while working in flood or sewer water, contact your physician or Health Department about receiving a tetanus vaccine or booster.
• Disinfect all areas, equipment, toys and objects that came into contact with sewer water with a solution of 1/2 cup of liquid chlorine bleach to a gallon of water. Bleach is the most effective method for removing bacteria and odor, but it can cause discoloration of many materials.
• Do not mix bleach with ammonia. This produces chlorine gas, a dangerous and toxic substance.
• Machine wash contaminated clothes in hot water and soap. Add one cup of chlorine bleach to wash water.
• Ventilate the affected area with floor fans and dehumidifier to properly dry the area.
• Do not use heat to dry closed building interiors. Mildew and expanded water damage may result.
• Small, loose rugs and wall-to-wall carpet installed on tacks can be cleaned professionally. In-plant cleaning is the best option. In-plant cleaning for wall-to-wall carpets that are glued down may not be practical or economical. All padding should be discarded.

What happens if the storm water doesn’t drain away from the street after the rain stops?

Street flooding can be caused by leaves or other debris clogging the storm water drain grate at the street level. Residents can help prevent this from occurring by cleaning the debris off the grate when the rain event starts. There is also the possibility the restrictor is blocked. The flow restrictors used to limit the amount of storm water entering the combined sewer have small 2 ½ inch diameter openings. If the restrictor becomes clogged, a city employee is needed to clear this blockage. DO NOT ATTEMPT TO CLEAR RESTRICTORS YOURSELF.

If the storm water doesn’t drain away two hours after a rain event or if it is damaging vehicles, please dial 311 (847-448-4311 outside Evanston) between the hours of 7 a.m. and 7 p.m. and state the location of the street flooding. If the flooding occurs after 7 p.m., call the Utilities Department after-hours emergency number at 847-475-6880.

Alley Flooding

Alleys can flood as well. If you observe an alley flooding, consider the type of alley:

• Gravel alleys do not have sewers. Unfortunately the Sewer Division is not able to help relieve flooding in these types of alleys. Consider petitioning to get the alley paved. Refer to the City of Evanston Alley Improvements page for the Special Assessment Paving process.
• Paved alleys with storm drainage structures can flood as well. The causes, correction, and prevention of flooding in paved alleys are the same as street flooding. Please refer to the street flooding section to find out what causes paved alleys to flood and what can be done to correct the problem.

Diagrams of the Old and New Sewer System

Old system – Combine Sewer System Only

New system – Combined and Relief Systems