Storm Water System Terminology

Skokie's comprehensive storm water runoff control program is a combination of on-street storage, detention facility storage and relief sewers. The following terminology is frequently used in explaining the program and is defined here to assist residents.

Catch Basin

An underground structure, usually at the curb line, with either a closed or an open grate cover on the surface. It collects storm water from the streets and right of way.

Combined Sewer System

A sewer system which conveys both sanitary sewage and storm water. When this type of sewer surcharges during rainstorms, combined sewage may travel up the house sanitary line into basements.

Detention Ponds

Depressed landscaped areas used to detain storm water runoff during heavy rainstorms. The ponds fill with excess water and drain into the combined sewer system at a controlled rate that reduces the chance of sewer surcharge.


A large, vertical shaft used to connect to the Metropolitan Water Reclamation District's Deep Tunnel system. During construction, dropshafts are used as an access way for workers and equipment and for removing excavation material. Dropshafts are used to convey sanitary and storm water from the Village sewer system to the Deep Tunnel.

Flow Regulators

A device located in a catch basin that restricts the rate at which storm water runoff enters the Village sewer system. These regulators cannot be manually adjusted. They are fixed openings that slow down the flow of water into sewers.


Large sewers which transport sewage and storm water from Skokie and other Metropolitan Water Reclamation District of Greater Chicago member communities to the MWRD treatment plant at Howard Street and McCormick Boulevard.

Private House Drain

The private drain is the connection from residential property to the main sewer. The drain carries waste material from the residence to the Village sewer. Maintenance and care of this connection is the property owners' responsibility.

Relief Sewer

Sewers installed to supplement and/or relieve the combined sewer system to prevent surcharging of sewage into basements.

Roadway Berms

A section of street pavement that is constructed to create mini dams to safely maximize the ponding of storm water on the street surface.

Storm Sewers

A sewer system that only conveys storm water.


When combined sewers fill beyond capacity, water may back flow into homeowners' basements.

Trunk Sewer

A main sewer pipeline. In Skokie, a pipe that is 60 inches-90 inches in diameter, to which smaller collector sewers drain.

Underground Storage Facilities

Large diameter concrete pipes or large concrete tanks built underground to detain storm water runoff during heavy rainstorms. The facilities drain into the combined sewer system at a controlled rate that is designed to prevent sewer surcharging. Some of these facilities are located under Skokie parks and public parking lots.