Page 14 - May-June2019 Vol37 No1

Vital Connection from page 13
and Lebanon Pike required jacking and
boring to keep a major railroad crossing
open.
Tracing the Loop
A 60" x 60" DIP Tee with two 60-inch
gate valves on either side was used to
connect the 60-inch replacement section
of transmission main on McGavock Pike
to the new 60-inch transmission main
routed toward the eastern portion of the
distribution system.
An MWS cost savings of $75,000
resulted from creation of an 84-inch
diameter tunnel routing the new section
of 60-inch ductile iron pipe beneath the
Nashville Eastern Railroad Crossing
near Donelson Pike. (The design team’s
decision to reduce the tunnel’s diameter
from 96 inches to 84 inches and shorten
its length played a significant factor
here.)
Garney Construction managed a
500-foot-long construction zone in
an area with a high volume of traffic,
moving the zone down the street
concurrently with construction efforts
to avoid blocking the entire length of
the street, minimizing impact to traffic.
This was particularly important since
the 60-inch transmission main was laid
in the middle of some of Nashville’s
central traffic routes, which are also state
highways managed by the Tennessee
Department of Transportation (TDOT)
and Metro Public Works, including
Donelson Pike—the main route to and
from Nashville International Airport
from the north.
Part of the 36-inch water main
alignment involved crossing the Stones
River near Lebanon Pike. Starting on the
west side of the Stones River, a temporary
Portadam was created to pump out river
water allowing workers to dig below the
riverbed to lay this section of 36-inch
water main. Coordination with the
United States Army Corps of Engineers
was required during this portion of the
construction to regulate the flow from
Percy Priest Lake into the Stones River.
Once complete, the same process
was employed on the east side of the
river, with the water transmission main
ultimately tying into the existing 24-inch
line at Central Pike, thereby completing
the water system loop.
Gresham Smith engineers worked
14 TPW May/June 2019
closely with MWS, Metro Public Works
and TDOT to complete the project on
an expedited schedule. Working around
the clock, the project was completed in
less than 24 months, saving millions of
dollars for MWS and mitigating impact
to the public.
The new route and distribution points
add enough capacity to the system that in
the event one water treatment plant goes
offline in an emergency, sufficient water
still could be effectively supplied to the
east side of Nashville.
In summary, the new water
transmission main pushes water via a
continuous loop that can accommodate
flow in either line, as needed, to
accommodate system water demand.
The new water transmission main
also provides increased reliability for
delivering clean water to the eastern
portion of Davidson County.
This system is better prepared to
handle a break, due to the increased
flexibility and the variety of directions
water can be pushed from either K.R.
Harrington or Omohundro—or both
plants. As a result, the water distribution costs were avoided by strategically
system is a more reliable infrastructure
for MWS customers.
A Socioeconomic and Environmental
Win-Win
While aging infrastructure systems
pose major issues, well-planned strategic
infrastructure projects often provide
exponential benefits both economically
and to the community. The CCL
Transmission Water Main project
identifies multiple social, economic and
environmental benefits to communities
similar to Nashville, in terms of how
infrastructure improvements can help
cities survive, adapt and grow.
Economic benefits included jobs
sustained during the project as well as
projected growth in economic activity.
Social and environmental impacts were
projected via literature reviews, data
analysis, and interviews with project
staff. Benefits included increased
resilience and reduced traffic congestion.
Environmental impacts were expressed
as the estimated reductions in external
costs to the community when traffic
congestion is reduced. When compared
to MWS’ already high level of service
and regulatory compliance, supply
redundancy was the benefit yielding the
greatest impact. As part of this project,
a Triple bottom line (TBL) analysis
was prepared to quantify the overall
economic, social and environmental
impacts.
In this context, by creating supply
redundancy for the MWS service area
east of the Stones River, this project
improved CCL’s transmission water main
resilience against the acute shock of a
water main break.
As evidenced in the TBL analysis, there
are current and future positive impacts
from infrastructure spending. In the case
of the CCL project, post-construction,
the redundancy accomplished by the
project is estimated to avoid $5.5 million
of additional expense and lost revenue
in the communities east of the Stones
River, in the event of future water supply
disruptions.
During construction, over 100
estimated jobs were supported, many
of them stable infrastructure positions;
an estimated $3.1 million in taxes
were collected across federal, state
and local jurisdictions; an estimated
$8.7 million in future construction
upsizing a portion of the line to 60-
inch pipe; and a verified $6.1 million of
construction was awarded to small or
disadvantaged businesses supporting
the project. Moreover, an estimated 1.4
years of additional traffic congestion
was avoided; $1.3 million in wasted
commuter work time and travel fuel
was averted; and $46 million of public
health and other external environmental
costs were avoided due to the expedited
construction schedule that was built into
the project approach.
The Cumberland City Lowdown
Without this project, MWS would still
have only one water transmission line
across the Stones River connecting the
entire eastern portion of its vital water
distribution system, creating a less than
optimal situation for the customers
they serve. With this project, MWS has
improved reliability, redundancy, and
resiliency systemwide, which benefits
the Nashville community by providing
a safe, clean and reliable water source.
New paving, spruced-up sidewalks, and
plantings along the former project route
are yet another positive byproduct of
one of the largest diameter high-pressure
pipeline projects in Metro Nashville
history.