Combined Sewer Overflow (NPDES CSO)
Most older cities in the United States were built with combined
sewer systems. This means that 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. During periods of
heavy rainfall or snowmelt, however, the wastewater volume in a
combined sewer system can exceed the capacity of the sewer system or
treatment plant. For this reason, combined sewer systems are
designed to overflow occasionally and discharge excess wastewater
directly to nearby streams, rivers, or other water bodies.
The EPA's CSO Control Policy, published April 19, 1994, is the
national framework for control of CSOs. The Policy provides guidance
on how communities with combined sewer systems can meet Clean Water
Act goals in as flexible and cost-effective a manner as possible.
One logical solution would be to entirely replace the combined sewer
systems in older communities with separate sewer systems, meaning a
separate pipe for stormwater and wastewater. However, this solution
is not feasible due to the tremendous costs involved.
In the 1970s, a team of engineers from the District, the City of
Chicago, Cook County and State agencies considered various plans to
solve the problem of flooding and water pollution in the Chicago
region. The hybrid plan selected as best and most cost-effective was
the Tunnel and Reservoir Plan — or TARP. Under this plan, 109 miles
of huge underground tunnels would be burrowed under the city to
intercept combined sewer overflow and convey it to large storage
reservoirs. After the storm had subsided, the overflow could then be
conveyed to treatment plants for cleaning before going to a
waterway. The tunnels are now complete and one of the three
reservoirs is on-line with the other two under construction.
The City of Des Plaines seven CSO’s are connected to the regional
TARP system. While the TARP is not yet fully complete, it has
already resulted in dramatic improvements in the water quality
throughout the Chicago region.
This web page includes links to the documents which outline the
City of Des Plaines’ efforts to minimize pollution and flooding
issues from the combined sewers as part of its federal National
Pollutant Discharge Elimination System (NPDES) Combined Sewer
Overflow (CSO) permit.
Additional Information
A full explanation of the NPDES CSO program and information about
combined sewer overflows can be found at the USEPA’s
website.
The Metropolitan Water Reclamation District (MWRD) maintains a
network of flow monitoring devices throughout the Chicago area to
detect combined sewer overflows. Up to date information is available
at the MWRD’s
website.
Information about the Tunnel and Reservoir Action Plan (TARP) is
also available on the MWRD’s website.
Living In Des
Plaines | Your
Local Government |
Your City Services
Economic
Development |
ADA Compliance |
Online City
Reference Desk
Search |
Site Map |
Site Use Policy
| Home
|
|
Engineering
