Ice Pigging - Award Winning, Pipe Cleaning Technology Using Ice
Paul Treloar – Utility Service Group
ptreloar@utilityservice.com
ABSTRACT
Sediment fats, oils, greases (FOG) and debris accumulation in wastewater collection systems clog
force mains and siphons causing pipeline restrictions. Restricted flows can cause increased energy
use, increased sanitary sewer overflows and can lead to capital improvements including increased
pumping capacity and force main replacement. Current approaches to clean force mains such as
cleaning with hard pigs and soft swabs present a risk because hard pigs can get stuck in the force
main causing a need for emergency excavation. Excavating to retrieve a hard pig is costly, time
consuming and in some cases with highways, river crossings and developed areas, is not an option.
Where redundant systems do not exist, the cost to install a temporary by-pass system may be
enormous. Other technologies, like flushing and water-jetting are inefficient and sometimes
ineffective. In addition, these processes use a lot of water which may not be readily available.
This paper describes a new technique for cleaning potable water, sewer force mains and siphons
using an ice slurry called, Ice Pigging.
KEYWORDS: Ice pigging, pipe cleaning, sewer force mains, sewer siphons, benefits.
INTRODUCTION
Developed by the University of Bristol, England, Ice Pigging is an award winning, innovative,
low risk, advanced pipe cleaning technology to clean force mains, siphons and better manage
pipeline assets. Utility Service Group (USG) is the sole rights holder in North America.
Ice Pigging has been proven to be between 100 and 1000 times more effective at removing
sediment and debris than water flushing alone. The ice slurry can be inserted and removed
through line taps, air valves, and other existing fittings so expensive excavations are not
required. Ice Pigging harnesses the characteristics of a semi-solid material that can be pumped
like a liquid but behaves like a solid once the pig is formed in the pipe
Because Ice Pigging relies on the natural glacial effect of ice to pick up unwanted sediment it
uses approximately 50% less water than standard water flushing and takes significantly less time,
typically the section of main being cleaned is out of service for no more than 30 minutes.
Traditional cleaning methods do have operational limitations that Ice Pigging can overcome. A
main feature of Ice Pigging is that it cannot get stuck, if for some reason the pig would get stuck,
we would allow the ice to melt and flush it from the main. Pipe bends, changes in diameter or
butterfly valves can all pose problems for swabbing or pigging, yet ice pigs can easily negotiate
these obstacles. To launch and receive traditional pigs, excavations have to be made to allow the
installation of launch and reception stations. This can mean costly, extensive interruptions to
force mains and siphons and require the installation of bypass pumping.
The Benefits
Ice Pigging represents a sustainable best practice
over traditional approaches to force main cleaning:
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It is efficient, rapid and environmentally
friendly.
It combines operational benefits of flushing
with the impact of solid pigging.
Ice Slurry injects through existing fittings.
System pressure pushes ice.
Suitable for pipes of all sizes and materials.
It effectively removes biofilm, iron,
manganese, FOG, grit and sediments.
Approximately 50% less water is wasted.
Produces quantifiable results.
Exceptionally low risk.
Figure 2. French press method of testing the ice
fraction
Methodology
To maintain the correct consistency of the Ice Pig, a freezing point depressant is used. USG uses
food grade, fine table salt (NaCl) which is approved by the National Science Foundation (NSF).
This is dissolved in potable water which is always sourced from the public water supply. The
current maximum batch capacity for USG is 2,700 gallons.
The brine is made in a 316 stainless steel delivery tanker and hose connections are made to the
ice machines that are mounted on a separate trailer (Fig.1.). The brine is fed into the ice
machines which, in turn freeze the liquid and return it to the delivery tanker. This cycle continues
until the ice slurry is at thickness known as the ice fraction. Ice fraction measures the amount of
ice crystals as a percentage of total volume. Ice fraction is related to the cooling capability of the
slurry compared to pure ice (100%); this is known as the Calorimetric Value. Ice Pig operators
use a simple French press coffee plunger (Fig.2.) to test the “ice fraction” (or the ice thickness)
on site prior to pumping into the main.
Typically, the thickest ice is used on plastic and sound concrete lined pipes as well as asbestos
cement, but when older unlined cast iron pipes are cleaned, a thinner ice slurry is used that does
not clean as aggressively. The thinner ice slurry will not
to disturb the buildup of tuberculation which could
damage the integrity of an old heavily corroded unlined
cast iron pipe.
Ice Delivery
Figure 1. Ice production setup showing the
delivery rig (left) and ice machines (right).
Setup for delivery varies slightly for each different
application. A typical setup for a potable water main is
shown below (Fig.3.). The delivery rig connects to the
inlet hydrant or other suitable fitting (2” or greater tapping with valve control), and at the outlet,
a Flow Analysis System (FAS) is connected. The FAS measures and records the flow, pressure,
conductivity, turbidity and water temperature as the water and ice are discharged. Once set up,
the main is flushed briefly to note and record pre-flush readings. The main is then isolated by the
owners’ operators and the required amount of ice is pumped into the main. At the same time, the
outlet hydrant is opened to create a flow and allow water to be displaced as the ice enters the
main. With careful control between the inlet and outlet, the flows are balanced to allow slightly
more ice into the main than the amount of water being displaced. This has the effect of the ice
forming as a pig against a pressurized wall of water.
Figure 3. Typical potable water main setup
Once the required amount of ice is in the main, the delivery pump is turned off and the upstream
valve is opened to allow the system flow and pressure to “push” the ice pig along the main
toward the outlet hydrant. The flow rate is controlled by the outlet operator at this time.
As the ice pig approaches the outlet, the conductivity reading will rise as the salty water of the
melting pig arrives in front of the pig.
The monitoring equipment will show the water temperature falling and conductivity rising as the
ice arrives. At this stage, the operator may collect samples of the ice at regular intervals for later
analysis. (Fig. 4.) The temperature and conductivity will return to pre-flush levels when all the
ice and salty water has flushed out of the system and the flushing shall continue briefly to allow
the turbidity levels to return to pre-flush levels or lower according to instructions from the
owner. The main is then returned to normal service. No
disinfection is necessary.
Figure 4. Taking samples
Sanitary Sewers:
The setup for sewer force mains
and siphons is similar to the water
main set up detailed above, except
no monitoring equipment is used
on the outlet. Instead, the ice is
pumped to a gravity main or the
WWTP. (Figs. 5. & 6.)
The delivery rig will connect to a suitable fitting for ice insertion. This may be an existing fitting
such as an air release valve (ARV) or a lift pump by-pass fitting. In the event there are no
existing suitable fittings, a 2” or greater tap and control valve can be installed.
Figure 5. Sewer siphon
On a typical force main, the lift
pump will be isolated and the wet
well will be allowed to fill to near
to high water level while the ice is
pumped in. The ice can only travel
in a direction away from the
pumps due to the check valve at
the pumping station (PS). The ice
will form as a pig against the head
Figure 6. Sewer force main
of water existing in the main. Once
the required amount of ice has
been inserted, the pump is turned on to give the pressure and flow to “push” the pig along the
main. The main is returned to service immediately.
Figure 7. USG's 2,700 gallon ice delivery rig
Figure 8. Various means of ice insertion can be via; From top left clockwise, a) fire hydrant, b) air release valve, c) pump bypass arrangement, d) pig launch station
CASE STUDIES
Western Hills Water District – Diablo Grande, CA. –Sewer Siphon - September 2013
Figure 9. Diablo Grande Community
Diablo Grande is a small community in the hills near Patterson California approximately 2hrs
south of San Francisco. The water and sewer system is run by Western Hills Water District.
There is one main sewer that runs by gravity over six miles
down to a WWTP in Patterson. It was designed to cope with the
large flows that future development will bring. The Sewer passes
under two aqueducts, the California Aqueduct and the Delta
Mendota Canal. At each aqueduct the main splits into two pipes,
Figure 10. Ariel photo showing the California one at a slightly higher level
Aqueduct and the Delta Mendota Canal
than the other to allow for
peak flows and is designed as a siphon to allow the contents to pass under the aqueducts by
means of a siphonic action. WHWD had noticed a reduction in the flow capacity and believed it
to be due to a buildup of sediment, grit and sludge at the low point of each of the siphon.
Although the main was designed with mechanical pigging launch stations at the high end of each
siphon, the engineer was reluctant to use this method in case the pig should get stuck in the main.
Designed and built into the syphon is the ability to flush the line with raw potable water from the
California Aqueduct. This connection can be used to inject large volumes of water into the sewer
line for flushing purposes. Unfortunately, the flushing had not proved effective on the buildup
causing a partial blockage of the siphons. USG advised WHWD that ice pigging may be the
solution rather than traditional pigging to eliminate the risk of getting a pig stuck under the
aqueduct where excavation for retrieval is not an option.
The theory was that if the siphons could be plugged off at the lower end, then the siphon could
be allowed to fill naturally from residual flow back up to the higher end point where the ice
would be injected. The stations were already in place for mechanical pigging so these were
adapted for ice injection. Once the siphon
Figure 11. Satellite image with blue highlighted route of the
was full, it could be isolated and the
gravity sewer detailing the two locations of the double barrel
residual flow meanwhile directed into the
siphons.
2nd bypass siphon. Ice could then be
injected into the full siphon while the
inflatable plug at the lower end would
allow water to be displaced via the flow
through pipe in the plug. This took very
precise communication between the USCI
operators at the injection end and the
contractors operating the flow through plug
at the "outlet" end.
Prior to this happening, a backup supply of
over 10,000 gallons of raw water was
pumped into the sewer at one of the
flushing points six miles away up at the community treatment works. This was the water that was
to "push" the pig through the siphon. It was estimated that it would take approximately three
hours for the backup water to arrive at the siphon once it was released.
Once the full tank of ice was injected, the flow throw plug was isolated thereby holding the ice
pig suspended in the first section of the siphon. It was then a matter of waiting patiently for the
backup water to arrive. The timing of this was pretty crucial so as not to allow the ice pig to melt
before being able to clean the main. After a few nervous moments, the backup water arrived.
Simultaneously, the plug was pulled and the flow diverted into the siphon containing the ice pig.
Again, a few more nervous moments waiting this time for the ice pig to arrive at the lower end of
the siphon.
Finally, the water started to darken in color and lumps of sludge and debris passed though the
manhole at the lower end of the siphon. The water turning darker and darker (signs of the melted
front end of the pig), and then, thicker and thicker. The decreasing temperature was monitored
using a thermal laser thermometer. Eventually, the ice was visible in the manhole and a huge
slug of ice squeezed out of the main. Once the main body of the pig passed, the fluid quickly
turned clear indicating the main had been thoroughly cleaned. The siphon was returned to service
and full flow was resumed. This concluded the world’s first known ice pigging of a gravity
sewer siphon using the award winning
technique.
Statistics
Delta Mendota Canal
Type of Main: Gravity sewer siphon
Length of main: 2 x 1,400Ft
Diameter and material: 12” & 14” HDPE
Ice quantity: 2,700 gallons
Ice fraction: 90%
Time main out of service: None
Results: Siphon returned to full flow
California Aqueduct
Type of Main: Gravity sewer siphon
Length of main: 2 x 3,151 Ft
Diameter and material: 12” HDPE
Ice quantity: 2,700 gallons
Ice fraction: 90%
Time main out of service: None
Results: Siphon returned to full flow
Figure 12. Ice being discharged from the siphon.
Middlebury, VT. Wastewater Force Main – October 2013
The Middlebury Main Pump Station conveys wastewater
through 12,000 LF of 16” and 18” ductile iron and 18” PVC
force main to the Wastewater Treatment Facility. During
some wet weather conditions, the pump station could not
keep up with incoming flows and raw sewage was
discharged to the Otter Creek (Combined Sewer Overflows
or CSO events). The pumps were able to discharge
6,200,000 gallons/day with two pumps running during the
first few years of operation (as designed), but pump rates
decreased by more than 10% (620,000 gallons/day) over
time as the force main collected grease, grit and sediment.
The project objective was to clean the force main by pigging
to regain the lost pumping capacity and eliminate CSO’s,
improve pump efficiency and save energy. It was
determined that “industry standard” solid poly pig
Figure 13. Utility Service Group - winners
of the ACEC Grand Award for engineering
techniques would not work due to the changes in pipe size,
no available insertion and retrieval stations, bends and wyes excellence on the Middlebury project.
in the force main that would have restricted travel and the
difficulty of handling the volume of water that would back
up into the pump station wet well if the poly pig got stuck. Because of this risk, a local contractor
would not even provide a quote. USG offered ice pigging as an exceptionally low risk solution.
Ice pigging was evaluated and determined to be the best solution given these conditions.
Calculations were made to determine the number of pipe segments to be “pigged” and location
of insertion points based on the pipe diameter, pipe length and the temperature of the wastewater,
to make sure the ice pig slurry would hold together as it traversed the pipe segment. The 12,000
LF force main was divided into nine segments with nine insertion points. Of the nine insertion
points, seven were located in existing air-release or clean-out manholes saving time and money.
The force main was exposed and taps were installed for the other two insertion points. The
project was completed on schedule over a three week period.
This project was the first use of ice pigging techniques to clean force mains larger than 8”
diameter in North America. It was also the longest continuous run of sewer force main (12,000
LF) successfully cleaned with ice pigging. The project demonstrates that large diameter force
mains (both ductile iron and PVC) can be cost-effectively and successfully cleaned by ice
pigging, avoiding other more expensive and invasive pipe cleaning and repair methods.
The ice pigging successfully cleaned the force main and force main capacity was returned to
6,260,000 gallons/day, based on daily draw-down tests at the pump station after each day of
pigging.
Figure 14. Drawdown tests show steady increase in flow after each operation.
Through ice pigging, accumulated deposits were removed, decreasing friction loss and
increasing capacity in the force main by more than 640,000 gallons/day. Pumping efficiency
was increased, lowering pump run times and saving energy and wear. The success of ice
pigging was evident each day when sand, grit, organics and grease discharged at the WWTF.
The increase in pump capacity should eliminate sewer overflows, protecting public health and
the environment. C-factor analysis has shown that the friction loss in the pipe is now typical of
that of a new pipe. After determining pumping velocities for different pump speeds, the Town
Engineer was also able to recommend programming changes in the pump cycles and pump
speeds to increase the velocity of flow through the force main during pumping to achieve a
“scour velocity” that should greatly reduce build-up of sediment in the future. Middlebury
should be able to operate the pump station at full capacity, saving energy and eliminating sewer
overflows for many years to come. Capital improvements to increase pumping capacity or
replace the existing force mains was avoided.
Statistics
Type of Main: Wastewater sewer force (pumped) main
Length of main: 11,772 Ft
Diameter and material: 18” PVC and Ductile Iron
Ice quantity for each run: 2,700 gallons
Ice fraction: 85-90%
Time main out of service: 1 hour max during each run.
Results: 15% increase in flow.
Dallastown Borough, Pennsylvania – December 2012
The first sewer force main in the US to be cleaned by
ice pigging was performed at Dallastown Borough,
located in South Central Pennsylvania. The Borough
was experiencing an underperforming waste water
pumping station and consulting engineers were
discussing capital upgrades the PS to meet the current
demands. After being introduced to the ice pigging
technology, the Borough agreed to an ice pigging
cleaning project as one last attempt to put off any
expensive capital improvements. No other options
were considered because of the long disruption to
service and cost of required enabling works.
Figure 15. Dallastown PA
This wastewater force main project of 1,200 linear feet of 4-inch diameter unlined cast iron
took approximately 2 hours to complete using 600 gallons of ice slurry. The ice was injected in
two batches to allow a primary partial clean followed by a secondary clean to clean out any
remaining sediment. This was done to avoid any potential heavy buildup of sediment in the
small 4” pipe.
The entire operation took just two hours and the ice pigging technology removed an obstruction
in the main increasing the pump flows by almost 30%. The Borough could abandon the capital
expenditure and put the money to good use elsewhere.
Statistics
Type of Main: Wastewater sewer force main
Length of main: 1,200 Ft
Diameter and material: 4” unlined Cast Iron
Ice quantity for each (of 2) runs: 300 gallons
Ice fraction: 80%
Time main out of service: 30 minutes maximum during each run.
Results: 30% increase in flow capacity
Stokes County NC – Distribution Network
The water system for the Town of Danbury is over 30 years old and is supplied by two wells,
both having some iron and manganese that over time had resulted in a buildup on the interior
lining of the system pipes. Regular customer complaints about discolored water made it
necessary to search for a solution and having limited water production capabilities and only
100,000 gallons of storage, flushing was not a viable option. A number of calls were made
looking for a company that had experience in pigging water lines and it was during those
inquiries that the client discovered “Ice Pigging”. After some research the Public Works Dept.
learned that Ice Pigging had many advantages over the more traditional cleaning techniques,
such as minimal interruption of service, up to 70% less water required, and no digging
necessary. The Stokes County Public Works Dept. identified the need to clean 18,500 FT of 6”
PVC potable water mains with the aim of removing as much sediment and manganese matter as
possible to improve water quality and reduce customer complaints of discolored water.
A desktop study was carried out at Utility Service Corporate Office using the water maps
provided by the Stokes County Public Works Dept.to measure out the lengths of pipe to be
cleaned in order to determine ice quantities and set out a proposed schedule of work. This was
backed up by a detailed site survey to determine the suitable insertion/extraction points.
Project objective: To provide a service that is a sustainable best practice method of cleaning the
water pipes using minimal amounts of water, giving the most effective results and with minimal
disruption to the water supply for the client’s customers. Project team: Consisted of a three man
team supervised by the Ice Pigging Project Manager. Project equipment: A 10 Ton ice delivery
tanker, a 10T ice production unit powered by a portable diesel generator and a Ford F-250
carrying a “Flow Analysis System”. Project features:
 Existing hydrants used to insert and extract ice.
 An existing fitting in a PRV pit was used for ice insertion on one run
 Entire project carried out in total 4 runs over 2 days
 Maximum supply interruption time 2 hours on each run
 Ice samples were collected for further analysis
 Waste tanker used to capture and dispose of the discharged ice.
Summary of results
Total length of mains cleaned
Average time taken per run
Average volume of water used
Average amount of sediment removed
18,500 FT
2hrs 20 minutes
1.6 x pipe volumes
87.6 lbs. per mile of pipe
SUMMARY
Ice Pigging in the United States
Over 300 miles of pipe has been cleaned worldwide using Ice Pigging, including 150 miles in the
United States across 28
states, (120 projects in all).
(Fig. 16.)
Pipes ranging from 2”-24”
diameter have been cleaned
and the maximum length
cleaned in one pass in the US
to date, is 2.25 miles on a 6”
PVC main in Murfreesboro,
Tennessee. USG continues
to apply Ice Pigging
techniques on potable water,
raw water, sewer force mains
and sewer siphons with
successful results. There are
upcoming wastewater
projects in Michigan,
Wisconsin, North Carolina
and Washington.
Figure 16. Map of US shows the green shaded states where Ice Pigging has been
performed.
Ice Pigging is being adopted as a cost-effective method of pipe cleaning in many countries
around the World. The experience gained by USG and others has shown that the technology
offers an opportunity to make real cost savings by reducing energy bills. More importantly, large
capital expenditure on new pumps, pipelines and structures can be avoided with a system that
provides the owner with a rapid, environmentally friendly, effective solution, at exceptional low
risk.
FREQUENTLY ASKED QUESTIONS:
Q. How much salt is used and what effect would it have on my Waste Water Treatment Plant?
A. USG use a brine solution with a similar salt percentage to seawater. The salt used as a
freezing depressant is food grade, NSF approved table salt. The effect on WWTP needs to be
considered as the salt can harm the good bacteria used in the treatment process. It is a simple
matter of dilutions and a question of what quantities the plant takes in a typical day. Generally,
the ice quantities are insignificant compared to the capacity of the treatment plant.
Q. Is it effective on cast iron pipes that have heavy tuberculation?
A. The ice is effective on any pipe material. A certain amount of care is required when applying
to heavily tuberculated cast iron. The ice slurry is prepared with a lower ice fraction, therefore, it
is runnier and less aggressive. This allows the pig to give an effective clean removing all the
loose sediment, biofilm and manganese buildup without breaking off too much of the
tuberculation.
Q. What pressure is required to push the ice through the main and will it require excessive force?
A. The ice flows through the main using the normal system flows and pressures. There will be
no undue pressure applied to the main. Prior to ice insertion, the static pressure shall be tested so
that the bar is set when inserting the ice. The operators have the experience and skill to control
the pressure by adjusting and balancing the flows as they inject the ice.
Q. Is the equipment clean or is there a risk of cross contamination?
A. The equipment is disinfected prior to every new project and at the end of every working
week. All hoses are disinfected, capped and stowed in clean boxes ready for use. There is a
separate set of hoses clearly marked for potable and waste water. No hose is ever used on a main
for which it is not designated.
Q. How will you dispose of the discharge?
A. Once the ice is delivered into the main, it becomes the property of the pipe owner. Disposal
will be according to the owner's instructions. Public sewer is the preferred choice but in the event
of the sewer not being suitable or available, then a waste disposal tanker can be arranged. A last
resort would be to discharge to ground but only after written State approval is obtained by the
customer.
Q. How does it perform in the heat of the desert?
A. Extreme temperatures are not the ideal situation, ice pigging can still be effective in these
conditions. Ice quantities would normally be increased to allow for the expected higher water
temperature. This may add to the cost to the customer so we may suggest that the work be done in
cooler periods in Spring, Fall or Winter.
Q. This is a pretty new technology, how can I be sure it is safe and will work effectively?
A. Ice pigging was developed over ten years ago in the UK. It was introduced to the US in 2012
and to date (September 2014), over 300 miles worldwide and 150 miles in the US have been
successfully cleaned. The operators are experienced and skilled, USCI has employed one of the
worlds most experienced ice pigging experts to oversee the service. There are a number of case
studies of our more notable projects on the USCI website and a list of references in the US is
available on request.
Q. Will the cold ice cause the main to break?
A. No. Tests were conducted on an
exposed pipe that was ice pigged in the
usual manor. Strain gauges and
temperature sensors showed no undue
stress on the main at all when the ice
passed through the main.
Figure 17. Temperature sensors and strain gauges attached to main
ACKNOWLEDGEMENTS
Figure13. By permission of Aldrich + Elliott, PC Water Resource Engineers.