Cleaning Large Diameter Water Lines by Ice Pigging
NC AWWA-WEA 2015 Spring Conference
Wilmington, NC
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John Collett
336-292-7490
Kevin Eason, PE
336-349-1042
Overview
• History of previous
distribution system issues
• Overview of ice pigging
technology
• Results from initial ice
pigging
• Plans for continued work
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City of Reidsville
• Water system has over
16,000 connections
• 3.28 mgd average day
demand
• Water treatment plant
supplied from Lake
Reidsville
• High seasonal
manganese and iron in
source water
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Distribution System Buildup
• In past years poor
treatment practices
contributed to
aluminum &
manganese deposits
• Received valid
criticism from industrial
customers regarding
water quality
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This contamination is nearly impossible to
clean from the membranes and, to this
point, require replacement of the
membranes. This is a cost of approximately
$16,000.00 per occurrence. To date since
October 2009 at least 4 known occurrences
have been noted.
In the past 6 months we have had an
unusual number of dirty water
occurrences. As you are aware clean
water for dyeing yarn is critical to providing
a quality product. The affects of dirty
water: additional costs for water due to
softener, backwash frequency increase,
labor costs for redyes of the affected yarn,
etc. The yarn dyed in our facility acts like a
filter and the sediment in the dirty water
attaches itself to the yarn causing off shade
dyeing among other quality issues.
Correspondence from May 2010
Distribution System Flushing
• Residents customers also affected
• Began unidirectional flushing
program in 2013 for water mains
12-in and smaller
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Buildup in Large Mains Found
• Heavy manganese
buildup noticed in
16-in pipe during
recent construction
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• City decided to explore options to
clean the larger diameter pipes in City
Cleaning Methods Considered
• Unidirectional Flushing
– Not effective for larger diameter pipes
• Mechanical Pigging
– Increased risk
– Install launch and
retrieval stations
– Butterfly valve removal
• Ice Pigging
– Lower risk, impact, and cost
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What is Ice Pigging?
• Cleaning technique that is operationally
similar to unidirectional flushing with the
impact of solid pigging
• Developed by the University of Bristol in
England
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• Utility Service Group
is sole rights holder
How Does It Work?
• Ice slurry is injected
into water main and
used to scour inside
of pipe
• Can be pumped like
a liquid but forms
into a semi-solid pig
once in the pipe
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Ice Production
• Ice produced on
location
• Food grade salt
used to control
consistency
• Additional chlorine
may be added as
disinfectant
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Ice Delivery – 10 Ton Load
• Ice delivery
truck brings
ice to site
• Slurry is
pumped into
pipe through
hydrant or
tap
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Ice Discharge
• System pressure used
to push ice pig
• Discharge flow
controlled using
monitoring box
• Pressure maintained
above 20 psi
• Temperature, turbidity,
conductivity measured
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Discharge Sampling
• Samples taken once ice pig arrives downstream
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Waste Handling14
Ice Pigging Site Schematic15
Specifics
• Cleaned 2” to 18” diameter pipe (so far)
• Target velocity = 0.5 fps
• Maximum length of run dependent on:
– Pipe diameter and material
– Water temperature
– Number of ice trucks used
• Can pass through fittings and butterfly
valves
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Reidsville Plan
• Deposits expected to
be heaviest leaving
the WTP and in the
southern portion of
system
• City decided to clean
24” pipe leaving WTP
and portions of 16”
pipe on Freeway
DriveBuildup Found
Ice Pigging Preparation
• Allowable length of runs determined by diameter of pipe, volume of ice per truck, and number of ice trucks available
• Layout runs and locate taps for ice injection and removal
Hydraulic Model Used During Planning19
Expected Demand During Pigging
• Average daily
demand Nov
2013 = 2.80
MGD
• Perform pigging
from noon to
5pm
Predicted Time Reidsville Tanks Can
Supply System Demand
Vance Street Tank Is First To Empty
1st Phase Of Work Complete22
1st Phase Of Work Complete
• Ice pigging complete
for 16” pipe
• Estimated 121 lbs
sediment removed
from 1,050’ of
16” pipe
• Lab analysis showed
significant amounts
of iron and
manganese removed
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2nd Phase Planned for May
• 10,500 LF of 24-inch pipe
• 2nd ice truck will double length of run
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Acknowledgements
• Kevin Eason – Public Works Director
• Scott Jewell – WTP Superintendent
• Scotty Wilkins & Paul Treloar – Utility Service Group
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Questions?26