Page 13 - May-June2019 Vol37 No1
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Treatment Plant or the Omohundro prestressed concrete cylinder pipe. routes were scored and ranked based
Water Treatment Plant. MWS, Gresham System resiliency was compromised on water quality, permitting, property
Smith, and Garney Construction acquisition, constructability, cost, and
provided professional services for due to previous breaks to sections of the schedule. Water quality was deemed
the comprehensive infrastructure circa 1970s 60-inch transmission main the most important and influential
improvement project, from initial from K.R. Harrington, with only one factor in selecting a route for the new
routing studies, design and bidding, transmission main (a 36-inch diameter transmission main.
through construction on an expedited pipe) serving the eastern portion of
project delivery schedule of less than 24 the distribution system. MWS sought a Maintaining a constant flow of
months. sustainable solution to address this aging water through water mains in a water
infrastructure challenge. distribution system minimizes potential
Using the CCL Transmission Water stagnation and thereby keeps water
Main project as an example, we explore To add redundancy to this essential age at an acceptable level. This helps
the significant benefits to system asset, MWS determined that a new water prevent the formation of disinfection
resiliency and the estimated economic, transmission main would need to be by-products and enables better-tasting
social and environmental benefits of designed and constructed to connect water. After the evaluation, the Elm Hill
constructing infrastructure projects. the existing 24-inch water main along Pike to Lebanon Pike route was selected
Finding the Right Solution Nashville’s Central Pike to the existing to become the alignment for the project.
60-inch transmission water main located
As Nashville’s population continues at the intersection of Elm Hill Pike and The most beneficial and economical
to grow, so does the city’s need for McGavock Pike. solution was to lay over five miles of
utility infrastructure improvements transmission main to intertie the water
and expansion. This is especially true of This would not only provide a loop system at the strategic locations of Elm
the eastern section of Nashville’s water system that could deliver water to the Hill Pike/McGavock Pike and Central
distribution system. MWS delivers clean Donelson/Hermitage area via two Pike. With the selected route and the
water to more than 200,000 customers means, but also improve overall water distribution system connection points,
in Davidson County through the K.R. system pressure. Moreover, this solution capacity in the distribution system
Harrington and Omohundro water also would decrease pumping costs by is increased, water can flow in both
treatment plants. reducing system head loss and bottleneck directions depending upon demand,
pumping pressure (which was inherent and reliability in the system is increased
Prior to the CCL transmission water with the single water supply line that against future water main breaks.
main upgrades, MWS provided water existed prior to the CCL project).
from its K.R. Harrington plant to the A significant project challenge involved
area east of the Stones River, via a single Gresham Smith’s engineers assessed tying the new pipeline into the existing,
36-inch diameter transmission main. available routing options for the new unrestrained pipeline. To mitigate this
This section of the system serves nearly main and provided a short list of three challenge, the Gresham Smith design
20,000 residents. MWS provided water proposed design solutions for further team incorporated a large thrust block
from K.R. Harrington to the rest of the evaluation. Each of the options began tied into rock, which prevented the
distribution system through a 60-inch at the intersection of Elm Hill Pike and unrestrained sections of pipe from
diameter transmission main made of McGavock Pike and terminated into moving. This innovative restraint system
the existing water distribution network was designed to withstand approximately
Stones River Crossing east of the Stones River. The proposed
1 million
pounds of thrust
under isolated
test pressure
conditions.
Additional
challenges included
placing the new
60-inch ductile
iron pipe into
ground that was
already occupied
by other utilities
and then creating
a path for it from
Elm Hill Pike to
Lebanon Pike.
For example, the
60-inch line near
the intersection
of Donelson Pike
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