Page 19 - Jan-Feb 2020

buildup or large debris. A junction box at
the far upstream end of the project and an
intermediate structure was constructed so
that the tops can be lifted off by crane to plishes for stormwater capacity and future
allow a skid steer loader to be lowered in
for future maintenance.
Pre-construction Soil and Groundwater
Characterization
For construction planning purposes,
S&ME was initially contracted by the
City to evaluate soil and groundwater
conditions along the horizontal and
vertical extent of the proposed stormwater
alignment. A total of 165 soil samples
were collected from 54 soil borings
and four groundwater samples from
monitoring wells positioned along the
three proposed conveyances.
The assessment activities identified the
presence of polynuclear aromatic hydro-
carbons (PAHs), eight Resource Conser-
vation and Recovery Act (RCRA) metals
and extractable petroleum hydrocarbons
(EPH) in soil and groundwater. For soil
samples containing metals concentrations
approaching or exceeding 20 times the
US EPA Toxicity Characteristic Regula-
tory Level, the samples also were analyzed
for the target constituents using the EPA
Toxicity Characteristic Leaching Proce-
dure (TCLP).
The assessments resulted in valuable
data necessary to support negotiation of a
Brownfield Voluntary Agreement for the
easement, provide recommendations and
protocols for management of foundry-
related waste and hazardous and special
waste as well as petroleum and metals
contaminated groundwater along the
portion of the alignment outside of the
landfill footprint.
Bringing Public Awareness of the Role of
Public Works and Engineering in Society
The public often is not aware of storm
infrastructure until there is a problem.
The City of Chattanooga identified
structural and capacity issues for the
existing storm infrastructure conveyance
under the Wheland Foundry Landfill,
proactively putting a plan in action to
relocate and upsize the existing storm
infrastructure to ultimately avoid a
catastrophic failure that would have both
environmental and flooding impacts.
Through public meetings, The City of
Chattanooga was able to spread awareness
about the project, discussing topics such
as the finding of contaminated soils, how
the project would address the soils in a
manner that contains and/or disposes the
contaminants to keep the public safe from
exposure, and what the project accom-
development.
Social, Economic, and Sustainable
Development Considerations
The stormwater infrastructure (that was
in place previous to the Big Dig project)
was undersized and already was partially
collapsed. The project limits were pri-
marily in an industrial area where many
properties have been vacant or dormant
for decades. While this project was driven
primarily due to the condition of the ex-
isting storm conveyance and environmen-
tal impact concerns, the project ties in to a manufacturers of the design options
larger effort to revitalize the St. Elmo and
Southern Chattanooga areas for invest-
ment and development.
The City has been in the process of
extending the Chattanooga Riverwalk
from the downtown riverfront to the
historic St. Elmo area. A portion of the
planned Riverwalk was incorporated into
the project, providing a key connection
to the upcoming Riverwalk project for
pedestrian and bicycle activity.
Extensive forethought went into the
design project. The storm infrastructure
that was installed with this project
was sized and stubbed out in multiple
locations along the alignment for
anticipated future expansion and
development. The Big Dig Project will
serve as the backbone to pave the way for
the future development in the area.
Complexity
Asset Inventory, Condition Analysis,
Hydrology, Hydraulics, Geotechnical
Engineering, Structural Design, Soil and
Groundwater Characterization, Utility
Design/Coordination, Environmental
Permitting, Wildlife Protection, Traffic
Control, Hazardous and Non-hazardous
Soil and Groundwater Management, Logis-
tics, Railroad Permitting, R.O.W./Easement
Acquisition, Construction Inspection/Ad-
ministration, Scheduling, Public Relations:
This list sounds like a pretty well-rounded
engineering curriculum, but these were
some of the key disciplines required to de-
sign and execute the Chattanooga Big Dig
project. This project was one archeological
find away from having everything!
Asset Inventory and Condition Analysis
One of the first objectives of this
project was to perform an inventory
and condition assessment of the existing
storm conveyance that was believed to
run underneath the Wheland Foundry
Landfill. What was found was a highly
deteriorated hodgepodge of partially
collapsed and eroded corrugated metal
pipes, box culverts, and parallel pipes that
did, in fact, run under the landfill. The
City was on the clock. They knew that if
the deteriorated pipe under the landfill
were to fully fail, it could have major
flooding and environmental implications.
Structural Design
The proposed storm infrastructure
was very large and very deep (ranging
from 22' to 30' below grade). Civic’s
engineers worked with multiple precast
for the storm conveyances. However,
the outfall structure and junction boxes
had to be specially designed. The outfall
structure required reinforced concrete
energy dissipaters that can stand up to high
velocity flows that may contain large debris.
Additionally, the upstream junction box
was three stories high and designed to tie
in to the existing upstream infrastructure
while allowing for bypass flow through the
structure during construction.
Continuous On-site Soil Management
Previous soil investigations conducted
by S&ME identified the presence of im-
pacted fill materials with contaminants that
rendered soils both non-hazardous special
waste as well as materials that exceed char-
acteristically hazardous threshold. S&ME
provided day to day on-site monitoring
services utilizing photo-ionization and x-
ray fluorescence instrumentation that kept
the contractors, Civic, City, and TDEC ap-
prised of site soil conditions continuously
for the duration of the project. The real
time evaluation of site soil conditions as-
sisted the contractor to direct the excavated
materials for reuse on-site as structural
fill, clean cover soils and off-site landfill
disposal as special waste.
Utility Design/Coordination
The project required the relocations of
gravity sanitary sewer, sanitary force main,
existing storm drainage, water lines, gas
lines, overhead utilities and even hydrogen
lines.
Traffic Control
Traffic control was integral in the success
of this project. The project required the
60-day closure of Broad Street (Cummings
Highway), which is one of only two main
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