Cleaning Large Diameter Water Lines by Ice Pigging

NC AWWA-WEA 2015 Spring Conference

Wilmington, NC

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John Collett

jcollett@hazenandsawyer.com

336-292-7490

Kevin Eason, PE

keason@ci.reidsville.nc.us

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

3

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