Underground Construction - August 2021 - 18

Five Steps to a Successful
Sewer Bypass Project
Neil Ripley
Use a spill containment berm at the
worksite. That includes placing a berm
under equipment, positioning it to
capture any fuel, oil or wastewater.
NEIL RIPLEY is a regional product
development manager with United Rentals Fluid
Solutions. He may be reached at nripley@ur.com.
For more information, visit unitedrentals.com.
Sewer overflows are a daily occurrence.
Clearing, repairing or replacing a pipe
usually requires a temporary sewer bypass
to divert the discharge from point A to
point B and create a work area.
Every sewer bypass project has
potential pitfalls. However, careful
planning, installation and monitoring can
reduce the risks of spills and leakages. For
any company designing, installing and
operating a sewer bypass, following these
five important steps can make project
success more likely.
Protect people, environment
Worker safety and environmental safety
always need to be at the top of the mind
with any bypass operation. That means
companies need to follow confined space
protocols. Anyone working in a confined
space, such as a sewer, should be properly
trained, equipped and supervised.
During sewer bypass setups and
teardowns, workers may be exposed to
raw influent wastewater that can carry
bloodborne pathogens. Encourage the
worksite team to have hepatitis A and B
shots to help protect themselves.
18 AUGUST 2021 | UCONonline.com
Size the bypass system right
Companies need to determine the
maximum anticipated flow and design of
the bypass system, including addressing
any site-specific challenges. A good first
step is to create a professional drawing
to conceptualize the bypass system for a
particular project site, and how the system
will address project needs and constraints.
This is an area where a professional fluid
solutions provider can have a major
impact on project success.
Sound attenuated, diesel-driven
centrifugal pumps are the typical choice
for the standard sewer bypass. However, if
the suction lift is too great, submersibles
or benching may be required.
Typically, in sizing the system, the total
dynamic suction lift should be no greater
than 25 feet. This measurement is taken
from the surface of the water (at its lowest
operating level) to the eye of the pump
impeller. The measurement also needs to
take into consideration site elevation (for
NPSHa purposes), as well.
The typical recommended submergence
depth is 6 feet. However, in certain
applications, both the suction lift and
liquid depth parameters may vary. A
suction lift that is too high or too low
can cause performance loss or equipment
damage. Also, design your system so
the suction velocity does not exceed
10 feet per second. To avoid potentially
rupturing, flattening or causing flow
surging inside the discharge line, make
sure the system is evacuating air with
strategically placed air release valves.
For the purposes of safety, a job site
should have - 100 percent of the time
- backup pumps plumbed in and at the
ready in case of mechanical failure of
the primary pumping system. If repair
onsite isn't feasible, project teams should
make it easy to swap pumps in and out as
needed. In set up, teams need to create
good access points for situations such as
fueling and preventative maintenance.
Keep the bypass
running smoothly
Here are a few tips that can help ensure a
bypass system operates properly.
Every project should be monitored by an
experienced, capable worker watching the
system 24/7, checking suction manhole
depths at a minimum of 15-minute
intervals. To complement pump watch
personnel, a telemetry system can be
installed to automatically send alerts for
problems involving fuel level, oil pressure,
coolant temperature, flow rate, suction
and discharge pressure, and more.
During times when the temperature
will dip below freezing, be sure to consider
ways to keep the pumping area warm.
When less than 32 F degrees, water that
isn't moving (such as running a system
using on/off floats) will freeze, and can
crack the volute in the pump and destroy
it. This can cause costly damage and, more
importantly, disrupt the bypass. Use space
heaters, electric blankets or tents, as
needed to help prevent freezing.
Check and test before startup
Fixing system performance issues
becomes much more complex once a
bypass system goes live. Here are some
ways to help reduce the risk of developing
system issues.
Even though each pump may have been
inspected by a qualified mechanic, it never
hurts to re-check all pump wet end, and
engine lubricant and fuel levels before
activating a bypass system. Additionally,
apply a vacuum plate to the suction side of
the pump to test for proper vacuum. After
a pump leaves the shop and is delivered
to a worksite, it may sit for days, weeks
or more before being ready to run. It is
sound practice to conduct some basic
checks one last time before installation.
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Underground Construction - August 2021

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