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
- 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
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
What will we do as sewage increases because of population
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
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
Are tunnels a proven technology for wastewater and CSO conveyance
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
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
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
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
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
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
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
What are the bottom-line benefits that the authorized plan
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
- 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.