Combined Sewer Overflow Controls in Southeast Michigan
Suzanne Coffey, P.E., Great Lakes Water Authority, E-mail Suzanne.Coffey@glwater.org
Majid Khan, PhD., Great Lakes Water Authority, Majid.Khan@glwater.org
Ed Hogan, PE, Wade Trim, email@example.com
Imad Salim, Ph.D., P.E., Wade Trim, firstname.lastname@example.org
Most large, older cities in the Great Lakes basin were located on the banks of rivers or lakes to meet the needs for transportation and commerce. Detroit was no exception. During the 1700s and 1800s, the streets were primarily dirt or gravel and they frequently remained muddy after rainfall. Citizens of Detroit and similar cities grew tired of muddy streets and urged the local government to do something about this inconvenience.
The immediate solution was to build sewers to drain storm water off the streets during wet weather so that they would not remain muddy for long periods of time. These sewers were either open ditches or pipes buried underground. As communities grew, these sewers needed to be quite substantial in size to carry away the storm water. Remember, of course, that the vehicles on these roads were horses and carriages, and that the horses left behind more than footprints. At that time, domestic water use was relatively low, but the domestic wastewater was simply dumped in the gutter where it would be flushed away during the next rain. During these rains, both domestic wastewater and manure from the streets were flushed into the sewers, where they were transported directly to the nearest waterway. This created both odor problems and pollution of waterways.
A new kind of sewer, called an interceptor sewer, was built to address these problems. They were primarily built parallel to waterways to carry wastewater further downstream. It was common and acceptable up to the late 1800s and early 1900s to move this wastewater further downstream where there were fewer or no people to complain. In the early 1900s, domestic use of water increased rapidly with human population growth and resulted in increased domestic wastewater discharges. Since the sewers at that time were originally designed to carry away storm water, the increased domestic wastewater from the growing population could exceed sewer capacity during heavy rains and snow melt. However, because of budget constraints, the sewers at that time were sized to intercept only the domestic waste during dry weather conditions. Therefore, one of two things had to happen during a rainstorm. Either the sewers would exceed their capacity and flood the streets or there needed to be a relief discharge directly into a waterway near these populated areas. Structures, called regulators, were constructed to provide this relief. They operate when the flow rises above the height of the overflow weir, allowing the combined storm and sanitary sewer flow to overflow into the receiving waterway – thus causing what has come to be called a combined sewer overflow (CSO).
As time went by, the idea of building sewers that handled both the sanitary wastewater and the storm water gave way to the concept of building a separate system just for sanitary wastes. These separate sewers came to be called sanitary sewers and the original type of sewer came to be called combined sewers. Today, these combined sewers are found only in older, larger cities where combined storm water and wastewater are treated during dry weather, but it overflows directly into rivers during and after wet weather events. When many of these combined sewers were constructed, they were simply called “sewers.” Later on, in the 1930s and 1940s, the distinction between storm sewers, sanitary sewers, and combined sewers became well accepted.
Status and Trends
In 1972, the U.S. Congress passed the Clean Water Act which launched a major effort to control pollution from industrial and municipal sources. The law required each state to issue discharge permits to regulate the quantity and concentration of pollutants from municipal and industrial treatment facilities to meet state water quality standards.
By the mid-1980s virtually all of the over 400 municipal wastewater treatment plants in Michigan had achieved compliance with the Clean Water Act requirement to provide secondary treatment of all flows. Michigan’s treatment plants were also required to disinfect the wastewater prior to discharge and reduce phosphorus loadings to control nutrient impacts in the Great Lakes basin.
As the discharges from wastewater treatment plants came under control, attention began to focus on water quality problems attributable to intermittent wet weather discharges from combined sewer systems. CSO discharges can be a significant source of pollution to receiving waters since they consist of a diluted mixture of untreated sanitary wastewater and storm water runoff. Water quality problems attributable to uncontrolled CSOs include public health threats from bacteria contamination and pathogenic organisms, dissolved oxygen depletion, aesthetic problems, and residues from sanitary trash and floatable materials. CSOs were a particularly significant problem in southeast Michigan because of the high population and the fact that CSO discharges were impacting small urban waterways such as the Rouge River and its tributaries. Within the service area of the Detroit wastewater treatment plant (now identified as the Great Lakes Water Authority (GLWA) Water Resource Recovery Facility (WRRF)), more than 25% of the service area utilizes combined sewer systems.
Within the city of Detroit there are 35,924 hectares (88,770 acres) served by combined sewers and an additional 24,186 hectares (59,764 acres) in suburban communities in Wayne, Oakland and Macomb counties (Figure 1
). Uncontrolled CSO discharges were identified as a major source of pollution throughout much of the Rouge River basin, the Clinton River basin, and portions of the Lake St. Clair and Detroit River shoreline.
In 1985, work began on the development of Remedial Action Plans for these watersheds to define alternatives for improving water quality and protecting public health. The Rouge River Remedial Action Plan was adopted in 1988 and called for substantial investment in facilities to control CSOs in Detroit, Wayne County and Oakland County. Similar control efforts were initiated along the Clinton River and Red Run Drain basin, and the shoreline areas of Lake St. Clair and the Detroit River.
The recommendations of the Remedial Action Plans were the basis for new permit requirements to eliminate or adequately treat CSO discharges throughout southeast Michigan. The southeast Michigan CSO control program received support from the federal government when Congress approved the Rouge River National Wet Weather Demonstration Project in 1992. Under this program, municipalities in the Rouge River watershed served as a pilot program to demonstrate the effectiveness of various CSO control measures. The program also instituted a variety of other pollution control activities related to storm water discharges, streambank erosion control, wetland preservation, public education, and other measures.
Areas of Wayne, Oakland, and Macomb counties that have combined and separate sewer systems.
Prior to 1990, there were more than 170 uncontrolled CSOs in existence in 35 municipalities in southeast Michigan. The quantity of untreated combined sewage discharged annually at that time is estimated at more than 119 billion liters per year (over 31 billion gallons per year), although the actual quantity of the discharge varies in response to climatic conditions and rainfall patterns. CSO discharges typically occurred about 50 times per year throughout the region and the pollutant load from these discharges was significant. Numerous water quality studies in the area documented serious impairments and water quality standards violations during and after wet weather events when CSO discharges occurred. Dissolved oxygen levels in some areas were depleted, making it difficult for the watersheds to support aquatic life and fish.
In response to the regulatory initiative to control CSOs, southeast Michigan communities in the GLWA service area have committed to the construction of projects totaling nearly $1.8 billion to eliminate, capture, or treat combined sewage, with more than an additional $400 million supporting the study, design and oversight of the CSO construction projects. A list of the CSO control projects is included in Table 1
. The debt obligation to pay for these capital improvements has had a significant impact on local sewer rates, even though many facilities were financed with low interest loan assistance from the State Revolving Loan Fund, and the initial projects received grant support through the National Wet Weather Demonstration Project.
CSO investment of southeast Michigan as of May 2007a
. DWSD = Detroit Water and Sewerage Department.
Listing does not include facilities to control sanitary sewer overflows (SSOs) from separated sewer systems except for equalization basins which were built to retain excess wet weather flows in newly separated combined sewer systems.
Construction cost reflects the cost to build the facility (as-bid contractor's cost plus or minus change orders) and has not been adjusted to account for inflation since the project was built. Costs do not include engineering, administrative, land acquisition or legal expenses.
The benefits of this massive CSO expenditure have become apparent as water quality throughout southeast Michigan continues to improve. The volume of uncontrolled CSOs has decreased substantially, and further improvements will be achieved as projects currently in design and construction are completed and placed into service. As shown in Figure 2
, the quantity of uncontrolled CSO discharges have been reduced by 95%, on average, with completion of all core elements of CSO Control Program. As the program moves into the final phases, the remaining control measures are focused at fully complying with the Michigan Water Quality Standards.
Historical and projected effects of Detroit Water and Sewerage Department’s, Great Lakes Water Authority, and customers’ efforts to reduce and treat CSOs.
Dissolved oxygen levels in receiving waters throughout southeast Michigan have shown steady improvement, and fish and aquatic life surveys document that area waterways are markedly improved. Because the CSO control projects typically include disinfection to control bacteria, recreational users benefit from improved public health protection practices, and beach closures in response to wet weather events have become increasingly infrequent.
While the effort to control wet weather pollution from CSOs is not yet complete, the progress achieved to date demonstrates that significant water quality improvements are achievable in urban areas when CSO controls are constructed. The overall health of the watersheds in southeast Michigan has experienced significant improvement, and is continuing to improve. In large measure this is a result of the work by local government to control pollution from combined sewer systems throughout the area.
Management Next Steps
Key management actions for southeastern Michigan watersheds include:
- Complete the GLWA long-term Wastewater Master Plan;
- Continue City of Detroit Green Infrastructure Program;
- Continue to strategically identify, evaluate and plan for the remaining CSO control projects;
- Continue sanitary sewer capacity improvements;
- Promote the economic importance of the region’s “Green” (plants) and “Blue” (waters) infrastructure to encourage adequate public investment in continued restoration and protection efforts;Ensure sufficient collaboration among all watershed communities, all watershed counties, Michigan Department of Environmental Quality, and the U.S. Environmental Protection Agency to secure adequate funding to sustain and expand a collaborative illicit discharge elimination effort and a public education and watershed monitoring program; and
- Integrate the combined sewer overflow and the storm water permit programs with receiving stream water quality for all southeastern Michigan watersheds.
Monitoring is essential for proper watershed management. Priority must be given to ensuring sufficient monitoring to be able to adequately evaluate effectiveness of programs and to make midcourse corrections. Further, research is needed on innovative funding mechanisms for storm water, CSOs, and watershed management in order to maintain the momentum for restoration and protection efforts.
Contact Information regarding Combined Sewer Overflow Controls in Southeast Michigan
Suzanne Coffey, P.E.
Chief Planning Officer & Interim Chief Operating Officer – Wastewater
Great Lakes Water Authority
E-mail Address: Suzanne.Coffey@glwater.org
Majid Khan, PhD.
Director Wastewater Operations
Great Lakes Water Authority
E-mail Address: Majid.Khan@glwater.org
Ed Hogan, PE
Senior Project Manager
E-Mail Address: email@example.com
Imad Salim, Ph.D., P.E.
Technical Lead for Wet Weather Planning
E-mail Address: firstname.lastname@example.org