What is the purpose of the Custer
Avenue CSO Storage & Dechlorination
The Custer Avenue CSO Storage Facility project &
Treatment Facility upgrades 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. This facility
is part of storage and treatment alternative that involves
capturing and storing overflows from combined sewers
that result from rainfall. The overflows are stored in a
linear storage facility. When the rainfall is over, the
captured CSO volume is conveyed via an existing
tunnel to a separate treatment system for removal of
pollutants and disinfection before discharge to
receiving waters. As parts of the combined sewer
system are separated, this same system can be used to
treat stormwater runoff from the urban core portion of
the CSO area.
Why is additional storage needed?
Additional storage is needed to increase the volume of
CSO that is captured and treated so that the volume of
partially treated overflow discharged to Intrenchment
Creek can be reduced to the level required to meet water
quality standards. During rain events, combined sewer
overflows travel to the Custer CSO facility and are
directed into an existing tunnel and conveyed to the
Intrenchment Creek CSO Treatment Facility. However,
during extended periods of rain, the existing tunnel
reaches its capacity and some overflows discharge to
Intrenchment Creek with only disinfection treatment.
The new storage facility will supplement the existing
tunnel storage capacity so that more CSO can be
captured and treated at the Intrenchment Creek CSO
How will the underground storage facility
To construct the new storage facility, a 30-foot diameter
vertical construction access shaft, approximately 120 feet deep, will be excavated
into rock. Its walls will be
reinforced with concrete where required for stability.
This shaft will provide access to start constructing the
below-ground storage facility. Contractors will
excavate into solid rock using drill and blasting
construction methods to create the storage cavern.
How was the alignment for the Custer
Avenue linear storage structure selected?
The alignment for the Custer Avenue linear storage
structure was selected based on the best possible rock
or geological conditions for constructing the
underground storage facility, proximity to the existing
tunnel, and minimum impact on private property.
How does this linear storage facility
compare to tunnels in Atlanta?
Although the linear storage structure is excavated
through mostly solid rock, existing tunnels are
considerably deeper than the depth proposed for the
Custer Avenue linear storage.
Will Easements be acquired for this
The City will be acquiring one subsurface easement
for this project. The remaining construction areas are
along city streets or city owned property.
How will safety concerns be addressed
with this project?
The City and its design engineer for the Custer Avenue
Tunnel are committed to maintaining the City’s
excellent safety record on all construction projects. The
City will continue to require the contractor to develop
and implement a safety program.
Will there be any odors associated with
the operation of the Custer Avenue CSO
The entrance at the top of the construction access
shaft to the linear storage facility will be sealed to
Will any streets along the alignment be
closed to traffic during construction? What
about construction truck traffic?
No streets will be closed. Trucks hauling excavated
rock from the shaft and underground storage facility
will only be allowed to turn left onto Custer Avenue to
Moreland Avenue to avoid residential areas as much
as practicable. The contractor will be required to keep
all streets free of refuge, rubbish, scrap materials and
Why won't the stormwater and wastewater
be separated in the entire Custer Basin?
Studies of the combined sewer system have shown that
the proposed additional storage and upgraded treatment
for CSO’s in the Boulevard CSO Basin is the most
economical and effective approach to meeting water
quality standards. Stormwater runoff from urban areas
is polluted with solids, bacteria and heavy metals and
will require additional controls in the future if water
quality standards are to be met in all streams and rivers.
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