Combined Sewer Overflow
The Rouge River National Wet Weather Demonstration
Project (Rouge Project) has been an unqualified success story in
many ways including the control of combined sewer overflows (CSOs).
This has been confirmed by independent sources. During the latter
part of 2001, USEPA's Office of Inspector General (OIG) conducted
a nationwide audit of the national CSO control program. The OIG
issued their final Evaluation Report on "Wastewater
Management - Controlling and Abating Combined Sewer Overflows"
in August 2002. The following is a quote from that report about
the Rouge Project’s CSO control program and the watershed
approach being utilized:
“Rouge River Project a Blueprint for Success
The Rouge River National Wet Weather Demonstration in Michigan is an excellent
example of how utilizing a watershed approach can help to achieve water quality
goals more efficiently. We have previously described in this report some
of the successful results that have been achieved by this project.”
The restoration of the Rouge River began by focusing on the primary
public health pollutant threat and source: combined sewer overflows.
At the start of the program, 168 CSOs were identified, with a tributary
service area of approximately 59,300 acres (approximately 20% of the
CSO controls are being implemented in the Rouge Project through three
phases as established by National Pollutant Discharge Elimination System
- Phase I: elimination of raw sewage and the protection of
public health for approximately 40 percent of the combined sewer
- Phase II: public health protection for the remaining combined sewer
- Phase III meet water quality standards in the Rouge River
Under Phase I, six communities separated their sewers and eight communities
constructed 10 retention treatment basins. Each of these basins is sized
for different design storms and several employ innovative technology.
These CSO basins also incorporate a variety of additional features or
variations in compartment sizing and sequencing in an effort to improve
their effectiveness. The retention treatment basins capture most wet
weather flows for later conveyance to the Detroit POTW for treatment.
Flows from very large wet weather events that are not captured by the
retention treatment basins receive screening, skimming, settling, and
disinfection prior to discharge. These CSO control projects have effectively
eliminated or controlled the discharge of untreated sewage from approximately
half of the watershed CSOs.
Working with the local communities, the Michigan Department of Environmental
Quality (MDEQ) established rigorous "Criteria
for Success in CSO Treatment" to
evaluate whether the CSO basins meet the Phase I and II goals of
elimination of raw sewage discharges and protection of public health
and the Phase
III goal of achieving water quality standards. The development of
an evaluation process provided an innovative forum for stakeholders
collaboratively establish objectives for CSO controls within the
goals of urban watershed restoration. Since wet weather control is
expensive, having a well defined, technical evaluation process to
with regulatory requirements is important.
A detailed evaluation study of each of the CSO control basins was
completed to examine the performance of the facilities and the resulting
water quality impacts of their discharges. The results of the evaluation
study, coupled with efforts to control storm water and other pollution
sources in the watershed, has provided valuable technical information
for use in establishing the basis for deciding on the Phase II and
Phase III CSO control program on the remaining CSO sources in the watershed.
In addition, the evaluation of design storms and control technologies
has provided valuable technical information for communities embarking
on such controls in other watersheds in the country.
As the CSO control program has been implemented, additional valuable
lessons were learned in the success of the control technology selected
at the various basins. Standard operation and maintenance procedures
are ensuring that the basins are meeting effluent limits and keeping
the basins as good neighbors to surrounding land uses, which include
nature centers, a golf course, and recreational facilities. A very noteworthy
finding was that while the technology was selected, installed and operated
so as to meet the Phase I objective (elimination of raw sewage and the
protection of public health), it was learned that the Phase III objective
(meeting water quality standards in the Rouge River) was also achieved
in many instances.
USEPA's 1994 National CSO Control Policy has been fully implemented
through the Rouge Project.
It is very important to note that the CSO control program, while at
the heart of the Rouge Project, is but one element of the overall Rouge
River restoration effort. The impressive improvements in water quality
and recreational use in the Rouge River can be attributed to the multitude
of other Rouge Project programs including illicit connection elimination,
storm water management activities, and developing better public, industry
and community awareness of pollution control and prevention. These programs
and others are all part if the watershed approach being successfully
implemented in the Rouge River watershed. For
more information on the watershed approach being utilized click here.
The Rouge River Wet Weather Demonstration Program has been successful
in identifying efficient and cost effective CSO basins for control of
combined sewer overflows. The wisdom of controlling CSOs at remote locations
versus trying to convey all of the combined sewage at one time to the
central treatment plant was confirmed. Combined sewer overflow pollutant
loads to the river have been cut by 90 to 100 percent during most wet
weather events. Demonstration basins, built to a smaller size than what
would have been required by presumptive criteria, have reduced release
of pollution to the river with excellent environmental protection results.
Protection of human health, elimination of the discharge of raw sewage,
and meeting water quality standards have been achieved, with the exception
of TRC, which is still being investigated. Phased implementation has
allowed lessons learned to be used in subsequent phases, affording greater
efficiencies in developing and implementing controls for the remaining
CSOs with a very large savings in capital expenditures. The completed
basins are controlling overflows at a rate of approximately 4 billion
gallons per year with outstanding water quality and aesthetic improvements
and increased recreational usage in the Rouge River.