When it comes to repairing aging
water mains, municipalities are always on the lookout for cost-effective and
less-intrusive technologies. Every repair made means more of the community’s
water is making its way from the plant to the user. But every repair has a price
tag.
The EPA estimates that in the last
20 years, communities across the US spent over $1 trillion to repair drinking
water treatment and distribution structures and wastewater treatment and
disposal systems. But with a growing population, continually aging water and
wastewater infrastructure, and increasingly limited funds, it is estimated that
by 2020 there will be shortfall in funding that could reach $500 billion.
With EPA’s data supporting it, and
communities relying on their own experience, new technologies for improving
water delivery are growing in number. But each technology must be evaluated for
its effectiveness and applicability, and just how it will work in the water main
repair toolbox. One Denver, CO, suburb tested a new solution and was pleased
with the outcome.
Identifying the Need
The city of Thornton, CO, is just
10 miles north of Denver and home to a population of just over 117,000
residents. The city itself is about 50 years old, as is much of the
infrastructure. Like any city, Thornton looks to maintain water treatment and
distribution services to its residents with minimal cost and disruption. So when
an alternative to standard trenching was suggested for water line repair, it
garnered attention.
The project area was identified
through GIS mapping. In the city of Thornton, when small leaks are identified,
they are entered into a GIS database. Over time, when certain areas show up
repeatedly, they are scheduled for repair. In the case of the Hoffman Way
project, a section of 50-year-old asbestos-concrete pipe hit the radar time
after time and was obviously in need of refurbishment.
Jason Pierce, project manager with
the city of Thornton, explains that Hoffman Way was used as a pilot program to
compare trenchless to open cut projects. The idea of going trenchless came about
because a portion of the project involves water lines buried below old, large
trees.
“We wanted to see if we could
repair the pipe with minimal disruption to the neighborhood,” says Pierce.
The city put out a request for
proposals and received bids from companies planning to use traditional trenching
and other trenchless technologies such as horizontal directional drilling and
centrifugal application to repair the stretch of pipe. W.S.U. Inc. of
Breckenridge, CO, won the project, proposing to use the company’s proprietary
MainSaver technology. The price came in at $140 per lineal foot for 2,000 feet
of 6-inch pipe. Pierce believes it’s realistic to plan future work to come in a
little higher, somewhere between $150 and $175 per lineal foot.
Harry Baum is president and owner
of W.S.U. Inc. His experience in the field started literally in the trenches,
doing excavation and rehabilitation work. His company has used the MainSaver
technology for two years, and Baum points out that its applicability comes down
to different factors, including the number of bends and valves, but none are
deal breakers. The only absolute condition that can stop a project is the
condition of the pipe. “We will look at the pipe, and we won’t say every reach
can be lined,” says Baum. “It may not be worth it, and it might be better to
have somebody dig it up and replace it.” Determining the feasibility of using
Baum’s technology comes in the initial phase of project work.
Step by Step
Like other technologies, MainSaver
is done through a series of consecutive steps. Typically, project execution
generally takes place in eight steps. The Hoffman Way, like other projects,
followed the steps listed here.
Replacing. Before any work is done
on the existing water line, it must be taken out of service, and a temporary
line established. The temporary pipe is connected either to a fire hydrant or
the main line, within an excavated pit. The temporary line generally runs across
the top of the ground and branches off, connecting to homes at individual meter
pits.
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Photo:
W.S.U. Inc.
New technologies for improving water delivery must be evaluated for effectiveness and applicability. |
Videoing. The existing water line
is examined. This requires excavations at two pipe locations. Pits are dug at
the launch and receiving ends of the pipe to be inspected. The distance between
launch and receiving can span upwards of 400 to 500 feet. Generally, pits are 4
feet by 6 feet across and about 4.5 feet deep to the top of the pipe.
“We TV the pipe and watch on a
closed circuit,” says Baum. “We can make sure that it’s in good enough shape to
rehab and locate the service laterals; we map them out so we know where they
are. Then we give the owner a report.”
If it’s decided that the condition
of the pipe warrants repair over replacement, the process moves on. In the case
of the Hoffman Way project, the pipes were deemed salvageable, and the project
moved on.
Cleaning. The pipe is then
cleaned, using pressurized water or mechanical rodding. “This can take from one
hour to one day to complete, depending on how dirty it is,” says Baum.
“Due to the buildup of mineral
deposits on the pipe, it was determined that cleaning the pipe was necessary,”
says Pierce. “The deposits can affect the grout consistency and its ability to
distribute evenly around the liner.”
Testing. Depending on the type of
pipe, Baum and his team then diverge from the normal lining process and test the
pipe for electrical conductivity. External pipe corrosion exists when the
outside of the pipe becomes the anode to the soil’s cathode, causing corrosion
of the outside surface of the pipe. Any corrosion that has taken place on the
outside of the pipe can’t really be repaired, but it can be held at bay. With
the use of a sacrificial anode, such as zinc or magnesium, the pipe can be
spared. To determine the best solution, Baum calls on geotechnical engineers to
collect soil samples and recommend the most suitable anode.
Asbestos-concrete pipes are
resistant to most external corrosions. In the case of the Hoffman Way project,
the pipes were in good condition, meaning no external remediation or sacrificial
anode was necessary.
Plugging. The service laterals
must then be plugged to keep the liner and grout that will be installed from
migrating out of the main line. In Thornton, W.S.U. introduced RoboTap, the
first commercial use of this process, to locate and cork the laterals. The
remotely operated robotic equipment travels the length of the pipe run, from
launch to receiving end, plugging the laterals and documenting their
location.
Lining. The lining comes in rolls
320 centimeters wide and makes its way from a plant in Barcelona to destinations
in the US. The inside and outside of the tubing are vastly different. The
outside is designed like Velcro, patterned with useful hooks. The inside is
smooth to not impede hydraulic conductivity. The length of the liner is pulled
through the pipe from launch to receiving end, going over any of the corks
placed at the service laterals.
Grouting. Once the lining is in
place, it must be kept in place. The liner is sealed to the host pipe by pumping
grout into the 3-millimeter-wide annulus between the host pipe and the liner.
The hooks on the Velcro exterior of the liner imbed themselves into the grout,
creating a composite-like material.
To ensure that the grout is evenly
distributed throughout the length of the pipe, a rounding swab is sent through
the length of the pipe. This pushes the grout into any pinholes, cracks, and
fissures. Approximately half a pound of pressure is applied using the swab, and
then it is left to cure overnight. The next day, the internal of the pipe is
checked using an infrared camera. The camera will pick up any gaps in the
grout.
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Photo: W.S.U. Inc.
The Hoffman Way project was used as a pilot program to compare trenchless to open cut projects.
W.S.U. Inc. won the project, proposing to use the company’s proprietary MainSaver technology.
|
When it comes to how much grout to
inject, more is better. “We use about 200% to 300% of the annulus volume,”
explains Baum. “We want more grout than we think we’ll need. The extra grout
goes out the end and becomes part of the backfill in the pit.”
The grout is subject to
temperature and must be between 45˚F and 55˚F. The grout is mixed on the spot,
so water temperature is critical and needs to range between 65˚F and 75˚F.
During the summer, this might mean adding ice to the mix water. During the
winter, it can be heated up using a heating iron. Admittedly, working outside
through the cold winter months isn’t something Baum is fond of, but he is
willing, and his technology is capable. “It’s not a deal breaker,” says Baum;
“you just have to make sure it’s addressed.”
Drilling. The liner is laid
through the straight length of pipe, but the homes cannot access it, as the
service lines are still plugged. RoboTap then returns to drill out the corks
that were installed at the service laterals. This is done by inserting a cap or
sleeve into the connection.
During the Hoffman Way project,
there was a slight glitch when it came to cutting through the grout. Since this
was the debut of the RoboTap, it needed to be adjusted for the 6-inch pipe. “The
top of the cap was too big to fit on the inner wall of the six-inch-diameter
pipe,” says Pierce. “But they were resized, and the problem was resolved.”
Once it’s determined that the
rehab work is complete, it usually takes another three to five days to return
the pipe to service. With water lines, the pipe must be disinfected following
local regulations. In Thornton, this included allowing chlorinated water to sit
in the pipe, and then performing a bacteriological review.
Broad Range
Applicability
The technology can be used on
pipes ranging from 4–12 inches in diameter, including concrete, ductile iron,
cast iron, steel, and asbestos cement. The process hasn’t been used on plastic
pipe yet, because it’s relatively new to the field, and to date there hasn’t
been a demand to repair plastic piping. But Baum doesn’t believe W.S.U.’s
MainSaver technology will have any problems rehabbing plastic when the time
comes.
All in all, the pipe inspection
and rehab can be done within one week: one day to open and inspect the pipe; one
day to cork the service laterals; one day to lay the liner and grout the pipe;
the grout then cures for a day before the pipe’s final inspection; add to that
the time to put the line back in service, and the schedule is complete.
“MainSaver is a good application
for certain projects,” says Pierce. “It’s not the Holy Grail, but in certain
applications it is cost-effective. The two biggest issues that impact trenchless
technology is the amount of asphalt and the number of fittings.”
The process is limited in pipes
with bends and cannot be used at tees. Pierce determined that for the Hoffman
Way project, because there were straight lengths of pipe at least 300 feet long,
MainSaver was a cost-effective alternative to traditional open trenching. “The
price goes up every time you have to dig an access point,” he adds.
But the cost of excavating access
points has to be compared to the amount of asphalt that will have to be trenched
through and replaced. While he found his own break-even point, Pierce
acknowledges that others may come up with different numbers.
As a result of going trenchless,
the City of Thornton was able to save approximately 50 mature shade trees and
avoid the replacement of 25 driveways. “The people paying for the work are the
people living in the houses,” says Baum.
“The project was shorter and
cleaner than open cut,” says Pierce.
And even with a slight delay in
schedule, people were ultimately pleased with the work. “We’ve had no
complaints,” adds Pierce.
Beyond
improving water delivery, avoiding customer complaints is a goal for any
community manager.