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Frequently Asked Questions

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What is a CSO?

A CSO, or Combined Sewer Overflow, occurs in a combined sewer/storm water system, where both storm water and sanitary sewage flow in the same pipe. These overflows were designed to prevent flooding at the wastewater treatment plants when the volume of rain exceeds the capacity of the combined pipes.

Why is it important to address the CSO problem now?

Although the City began addressing its CSO problems 20 years ago by building facilities to treat overflows, in 1995 the City was sued by the U.S. EPA, Georgia EPD and the Upper Chattahoochee Riverkeeper et al, who claimed that the facilities did not prevent violations of water quality standards. In 1998, the City signed a court-ordered Consent Decree agreeing to eliminate CSO water quality violations by November 2007.

What is the authorized CSO Plan that is authorized by the EPA and EPD?

The City submitted a plan to EPA and EPD in April 2001 describing how the CSO problem would be solved. That plan was authorized by EPA and EPD in July 2001. The specific elements of the plan are:

  • Separate a minimum of 27% of the combined sewer system. Meeting this minimum will increase the City’s total separated area from 85% to almost 90%. The areas to be separated will be chosen based on water quality benefits and how cost-effectively they can be implemented.

  • Construct a deep-rock tunnel storage and treatment system to capture and store 85% of the combined storm water and sewage flow for conveyance to two new CSO treatment facilities for advanced treatment (a much higher level than the current CSO treatment facilities provide) before discharge to the Chattahoochee or South Rivers. The number of overflows will be reduced from 60-80 per year to an average of only 4 per year at the 7 existing CSO treatment facilities. These remaining overflows will be screened, disinfected and dechlorinated before discharge to a receiving stream.

  • The new CSO treatment facilities will use chlorination/dechlorination, a highly effective method of killing bacteria that eliminates the need for chlorine disinfection. While chlorine is an effective method of killing bacteria, it can harm aquatic life. At the existing facilities where chlorine will still be used, dechlorination will be added so that treated discharges do not contain harmful chlorine residual.

The authorized plan is currently being refined to identify which areas of the combined sewer system will be separated. The refinement includes a predesign sewer separation study to determine where it is most cost effective to separate. The authorized plan provides for separating a portion of each basin, but EPA asked the City to look at fully separating at least one of the basins. By fully separating one or more basins, the City will be able to reduce the length of the proposed tunnels and eliminate one or more of the existing CSO facilities. This could reduce the cost and the number of facilities in neighborhoods. The long-range 2008 to 2030 wastewater plans will use information from the study for future planning purposes should there be funding available to consider additional separation.

How much is this going to cost?

The entire sewer improvement program is estimated to cost $3 billion. The estimated capital cost for the authorized CSO Plan is $950 million.

How will the sewer improvements be paid for?

Ratepayers will pay for the improvements unless state and federal funding assistance is secured. Without any outside funding assistance, we would expect water and sewer rates to triple over the next twelve years. The average bill is expected to increase gradually from annual average of $632 presently to $1,776 in 2014.

Mayor Franklin is actively pursuing alternative funding to pay for the work, including local sales tax, state and federal grants, and other sources of funding. Mayor Franklin is committed to easing the burden on ratepayers as much as possible by choosing the most responsible solution while seeking ratepayer relief.

How long will this proposed solution last? Will we have to fix this again in a few years?

The plan authorized by the EPA and the EPD is a long-term solution. The tunnels and treatment plants will be operational for several decades. Moreover, if all sewers are eventually separated, eliminating the need for the tunnels and treatment plants, these can be transferred to the future storm water utility for use as storm water management facilities.

Has the decision been made to go forward with this plan?

This plan has been authorized by EPA and EPD. However, the predesign process has revealed opportunities for refining the plan. The refinements may result in some modifications in the original plan. The City is continuing to gather information and seek expert advice in order to ensure that the best plan is implemented. The city will select a plan that: (1) meets the Consent Decree deadlines; (2) improves water quality; (3) is affordable; and (4) recognizes quality of life issues.

When will the Mayor reach a decision?

The final CSO plan will be submitted to EPA and EPD in early fall 2002, once the options for refinements have been studied and the costs and schedule are fully understood.

Will the city's CSO plan meet the timeline mandated by the court so that the city avoids the fines?

Yes, the authorized plan can be implemented by the 2007 Consent Decree deadline.

What will we do as sewage increases because of population growth?

The improvements to our wastewater treatment plants take into account projected growth in the City for 40 years. Should our growth exceed the treatment capacity of our expanded and upgraded plants, it will be necessary to do further capital improvements or to explore regional treatment solutions. However, we believe we have planned adequately.

Are we getting the best bang for our buck?

Yes. The authorized plan best meets the City’s four objectives: -

1. Minimize cost – The plan must be affordable for all of Atlanta’s ratepayers
2. Maximize water quality – The plan must meet all water quality standards
3. Meet deadlines – The City cannot afford to pay fines for missing court-ordered deadlines
4. Recognize quality of life issues – The public has expressed a preference for sewer separation where feasible

In addition, the plan allows the city to meet anticipated storm water regulations by providing treatment of storm water in the tunnel and storage system.

Will there be an economic benefit (more jobs)?

The number of construction and related projects under the City’s comprehensive sewer improvement program would create many jobs. In addition, the improvements are essential to continuing to attract new businesses to our city

Will the construction displace anyone?

The construction will occur in public rights-of-way, and very little displacement is anticipated.

What is the purpose of the tunnels?

The CSO tunnel project is one part of a comprehensive plan for long-term control measures to bring the City’s combined sewer system into compliance with water quality standards. The tunnels are part of a storage and treatment alternative that involves capturing and storing overflows (that is, CSOs) from combined sewers, resulting from rainfall. The overflows are stored in large underground excavated tunnels in bedrock. When the rainfall is over, the captured CSO volume is conveyed to a separate treatment system for removal of pollutants and disinfection before discharge to our streams and rivers. As parts of the combined sewer system are separated, the tunnel system can be used to treat storm water runoff from the urban core portion of the CSO area, which includes the central part of Atlanta, encompassing downtown, Midtown (near Piedmont Park), the Georgia Tech and Georgia Dome areas, and parts of east Atlanta near Grant Park.

Are tunnels a proven technology for wastewater and CSO conveyance and storage?

Yes, large underground tunnels are a common and accepted technology for conveyance and storage of wastewater and combined sewer overflows. A recent inventory of tunnel projects in other cities identified more than 47 tunnel projects in the United States and overseas. These projects ranged from 7 feet to 33 feet in diameter and from 2 miles to 33 miles in length. The Chicago Tunnel and Reservoir Plan (TARP) is one of the most successful and large-scale applications of tunnels. This project has 109 miles of 33 feet diameter that have performed excellently in more than two decades of operation. Other large tunnel projects in operation in the U.S. include Austin, Boston, Cleveland, Houston, Detroit, Los Angeles, New York, Minneapolis, and San Francisco.

Are there other deep tunnel projects in the Atlanta area?

The City of Atlanta owns and operates two deep sewer tunnels -- the Intrenchment Creek and Three Rivers Tunnels. These tunnels have been in operation for about 15 to 20 years and are functioning exceptionally well. Both tunnels were constructed through the metamorphic rock common in the north Georgia Piedmont, using tunnel-boring machines (TBMs). The Intrenchment Creek Tunnel is about 1.76 miles long and has a diameter of 26 feet. The Three Rivers Tunnel is about 7 miles long and has a diameter of 10 feet. These tunnels were constructed at depths of up to 270 feet below ground surface. The City, accompanied by its design specialist, inspected the Intrenchment Creek Tunnel in August 2000 and found it to be in excellent condition. Tunnel performance has been exceptional, and no environmental problems have occurred as a result of tunnel operation.

Won’t the underground tunnels pollute the underground aquifer? The implications of that are long-term and affect the entire region, don't they?

The tunnel is being constructed at a depth below the water table. Therefore, flow is more likely to seep in than out of the tunnel. In addition, the tunnel will be lined at strategic places to prevent any inflow or infiltration.

Combined sewer flows on the east side of Atlanta will go to the existing upgrade Intrenchment Creek plant. Where will the new CSO facility be put to handle flows on the west side?

The new facility will be located near the existing R.M. Clayton WRC, on the site of an old steam plant once used by the City’s Water Department.

Why put the treatment facility near the R.M. Clayton WRC?

To relieve neighborhood creeks and streams, we would discharge the highly treated combined flow from the new treatment facility directly into the Chattahoochee River.

Why is the City promoting a plan that still involves four overflows of combined sewage?

The National CSO Policy limits overflows to an average of four per year, and the City’s plan recognizes and complies with this. Any overflows from the CSO system will receive screening and disinfection before discharge.

Were other alternatives studied?

Yes. The City studied many alternatives, eventually eliminating all but 3. Those 3 were:

  • Option A: 80% sewer separation (separation of all but the downtown area, with limited storage and treatment for that area) $1.25 Billion

  • Option B: Storage and treatment only $700 Million

  • Option C: Partial (27%) sewer separation with storage and treatment (the currently authorized CSO Plan) $950 Million

Four criteria were used to evaluate each option – (1) ability to achieve water quality standards; (2) affordability; (3) acceptability; (4) ability to meet Consent Decree deadline. Storage and treatment only, the least costly of the three options, was eliminated because of the strong support for sewer separation expressed throughout an intensive 30-month public participation process. Full separation was not chosen because it was found to be the most expensive and most disruptive of the alternatives, could not be completed by the Consent Decree deadline and, by itself, would not offer the same water quality improvements as would the authorized plan.

Why won’t the City separate all the sewers?

The City’s analysis of full sewer separation indicates that it cannot be implemented by the Consent Decree deadline and is more costly. We also believe that separation of the sewers in the downtown urban core, which is highly developed, is impractical because of the disruption that would be required. Other findings from the analysis include:

  • Full separation alone will not achieve water quality improvements comparable to storage and treatment. According to an independent study commissioned by the Upper Chattahoochee Riverkeeper, the City's plan results in better water quality than full separation over a 40-year time frame.

  • Storm water ponds, detention structures or other storm water management techniques must be incorporated with sewer separation to achieve pollutant reductions comparable to what the City’s plan achieves, particularly in the more dense areas of the combined system.

  • Storm water ponds and detention facility costs would add over $1 billion more to the cost of full separation. The City cannot legally fund storm water ponds with water and sewer revenues. The general fund would have to bear the burden of the storm water management cost. The City cannot impose such an expensive option upon Atlanta taxpayers at this time. Although the City plans to establish a storm water utility to address storm water management Citywide, it could take several years to implement.

  • At present, there is no credible evidence to suggest that full separation can be completed by 2007. If we miss the deadline, we will have to pay fines of $8,500 per day and more.

The combined system represents 15% of the city – 85% is already separated. Following implementation of the City’s current plan, about 90% of the City will be separated. Pre-design refinement of the plan could result in an even greater area of separation.

Why is it so hard for Atlanta to separate its downtown area? Rome, Augusta and other cities have.

Rome and Augusta are not comparable to Atlanta in size and other parameters, so a comparison to these smaller cities is not meaningful. Of 18 cities of similar size surveyed, only Minneapolis/St. Paul has implemented full sewer separation, over a 50-year period. The downtown area was separated over a period of about 10 years.

If the sewers are separated, will storm water be treated?

Separation of sewers will completely eliminate combined sewer overflows in those areas, but will not provide treatment of storm water. Storm water management will be desirable at some point in the future but is not a part of the CSO Remediation Plan. Pre-design information for this portion of the plan will be used in the development of a long-range storm water management strategy for the City.

We heard that the city is eligible for and should request a time extension. Wouldn’t this allow full separation?

The EPA allows additional implementation time based on the affordability rating they assign to mandated capital improvement projects. Atlanta’s CSO project was rated “medium” in terms of its financial burden on Atlanta’s ratepayers. The medium burden rating automatically qualified the City for a 3-year extension. However, according to regulatory interpretation, the implementation period began in 1998; therefore, at most the City would gain an additional year to implement the program beyond 2007. The analysis of full separation does not suggest that it can be achieved by 2008. No formal request for an extension has been made as yet.

The SSES repair work is going to involve opening up the city streets to replace old sewers. Why not just separate while that's being done?

The SSES work was designed to use the least disruptive methods as possible. Therefore, much of the work will involve technologies other than open trench sewer work, such as pipe lining and microtunneling. There will be very limited open cut work.

Won’t separation create more greenspace opportunities?

Parks and greenspace are desirable. However, our preliminary analysis suggests that land acquisition alone may cost more than the City’s plan of improvement. The City has a separate greenspace acquisition program, which will work in concert with stormwater management. The city is working with other programs designed to provide parks and greenspace. Moreover, by law, the city cannot purchase land for greenspace with water and sewer funds.

You used water and sewer funds to pay for the Greenway acquisition program. Why are you saying you can't use them to do stormwater treatment in the areas that you separate?

The Consent Decree required Atlanta to purchase greenway space with money that would have otherwise been paid as fines. The City’s charter says that water and sewer funds cannot be used to pay for storm water treatment.

Does sewer separation become more expensive if you wait until the city is more developed?

Possibly, as land prices continue to escalate in the inner city and more development occurs.

It has been said that many other cities are using storm water ponds and that they are a better, more natural solution than engineering solutions.

Other cities have certainly used storm water ponds, but almost always in combination with an existing engineering solution and typically on a much smaller scale than what is being proposed in Atlanta by the natural systems advocates. It is important to take into account each area’s unique topography. In Atlanta, we generally have heavy rainfall and many small urban streams feed into relatively small rivers. This condition does not support storm water ponds as an ideal solution.

The City of Atlanta permits approximately 200 stormwater management facilities per year (vaults and ponds) associated with private development. It is probable that ponds will be an integral component for stormwater management in the entire City once a stormwater utility is established. However, water and sewer funds cannot be legally used to create such facilities. In the interim, the tunnel storage and treatment option offers the opportunity to treat stormwater from the combined sewer area in dedicated treatment plants to achieve a very high level of water quality, comparable or better than that achieved by stormwater ponds. The use of the tunnel and treatment system in the future will reduce the volume of stormwater that must be treated in surface ponds within the combined sewer area, thereby reducing the land area that must be dedicated to ponds.

Does the authorized plan have a greater impact on minority communities (especially the tunnels and treatment facilities)?

The tunnels will be constructed using a boring technique that minimizes surface disruption. In addition, the tunnel alignment is mostly in the public right-of-way so that neighborhoods will be largely unaffected. The tunnels will be underground in parts of northwest, northeast and southeast Atlanta, underneath many communities of varying income levels and demographics. All Atlantans, including those living in low-income and minority communities, stand to benefit more from the elimination of overflows that impair water quality in the creeks and streams that flow through their neighborhoods.

What are the bottom-line benefits that the authorized plan provides?

The authorized plan:

  • Is more cost effective. The authorized CSO Plan provides the best balance of water quality improvement and cost effectiveness. More pounds of pollution per dollar will be removed by the authorized plan than by other alternatives studied by the City.

  • Meets the mandated deadline. The authorized CSO Plan and the refinements being studied can be fully implemented by the 2007 Consent Decree deadline.
    ? Provides overall improvements to water quality in the combined sewer area. The authorized plan provides better removal of the pollutants of concern throughout the basin: total phosphorus (TP), copper (Cu), zinc (Zn) and total suspended solids (TSS). The plan also provides necessary sewer repairs and capacity fixes in the combined sewer area.

  • Provides improvements in the combined sewer area. The plan provides necessary sewer repairs and capacity fixes to prevent overflows in the combined sewer area.

  • Requires less community disruption. The tunnel will be constructed using boring equipment that minimizes surface disruption. The tunnel alignment is mostly along public right-of-way, to minimize disturbance to communities.

  • Offers storm water treatment. The tunnel storage and treatment system allows treatment of storm water along with sewage. Water pollution has many sources, and stormwater is a significant one. State regulations are already being developed to require storm water treatment. Storm water treatment in areas where the sewers are separated will require additional funding. Storm water treatment structures (ponds, filters, detention basins, etc.) cannot be funded with water and sewer dollars, and there is currently not a dedicated fund for storm water.

  • Assures the best overall investment. At $950 million, the authorized plan provides the best overall benefits for the money invested. The refinements being studied would provide a tradeoff of benefits, trading the treatment of stormwater for elimination of CSOs in some basins.

Why ask for citizen input if you are not going to use it?

The city has used citizen input. Citizen input was sought and used throughout the development of the CSO Plan. The plan submitted to EPA and EPD in March 2001 incorporated sewer separation at the request of citizens. The storage and treatment option was less expensive, but the City incorporated 27% separation of the CSO area into the CSO Plan in response to citizen input.

Can the city provide more written information to disseminate to the community? How can we get more information? Is there a phone number?

Written information is available. We are also available to make presentations in the community. Please call the program hotline at 404-529-9211 for information or to schedule a presentation.


Copyright 2007 City of Atlanta, Depart of Watershed Management. All rights reserved
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