Preparation for Depressurization:

How to Survive a Major Water Main Break

Dr. Thomas Marshall, PECity of Delaware

Dan Barr, PEBurgess & Niple, Inc.

Objectives of this Presentation

1) Present a case study of a recent major water main failure in the City of Delaware in order to provide insight into proper response and lessons learned

2) To learn the advantages of a having a calibrated water model

during a water main break

Case StudyCity of Delaware 16”

Transmission Line Break

Dr. Thomas Marshall, PE

City of Delaware

Case StudyCity of Delaware 16” Transmission

Line Break of December 2005

• Introduction

• Background

• Logistics and Response

• Lessons Learned

Case Study: Introduction

• City of Delaware, Ohio is located approximately 30 miles north of Columbus

• Established in 1856, the community has aging infrastructure in addition to a recent surge in growth – one of the highest growth areas in the nation

• Projects currently under contract total over $75M and include a wastewater plant expansion, elevated water tower construction, multiple water, storm and sewer line projects, and water treatment plant expansion planning

Case Study: Background

• 12/28/06 11:15 A.M. Contractor snags 16” transmission main which supplies 70% of the City’s water

• The other 16” main supplying the City dates back to the 1800s and will convey less than 30% of the City’s 6 MGD average daily demand

• The level in both of the City’s 1 million gallon elevated storage tanks began dropping rapidly

• Major portions of town were experiencing lower water pressures

Case Study: Background

• OUPS ticket was misread, wrong line was marked

• Line was not shown on project plans • Multiple pipeline projects were in progress in the

area• Line located in the back of the Delaware County

Fairgrounds – 6’ to 8’ of debris and backfill was placed over line since installation

• City, contractor, engineers, and EPA very short staffed due to Christmas Holiday

Case Study: Logistics and Response

The following steps were taken within approximately 30 minutes of the failure:– Distribution Superintendent was informed of

incident– Water plant operator, support staff, police, fire

and City officials were immediately informed– Incident command center was established at the

site – crews were called in to respond– OEPA was notified and consulted– Burgess & Niple was contacted to evaluate the

impact of the break using the distribution model

Case Study: Logistics and Response

Steps that followed:• Immediate efforts focused on isolating failure• Emergency connection to adjacent water

purveyor was activated• City officials implemented reverse 911

emergency system for affected customers• Media outlets advised• Ongoing Water Model and field data collection• Ongoing OEPA communication• Elevated storage tanks still draining at an

alarming rate

Case Study: Logistics and Response

Steps that followed (continued)

• Break was isolated – This was complicated by connections to the line that were not shown on old, inaccurate subdivision plans.

• Elevated storage tower elevations perilously low• A plan for repairing and disinfecting the line was

developed with guidance from OEPA• Repair was made• Disinfection plan was implemented

Case Study: Logistics and Response

• Disinfection Approach– HTH was used to super-chlorinate the 2250 feet of

depressurized main for 30 minutes

– Samples were taken and analyzed for chlorine residual at both ends of the isolated segment of main after 30 and 90 minutes

– Chlorine residual values of the 30 and 90 minute samples were compared – values were unchanged• A reduction in chlorine residual from the 30 to 90 minute

samples would indicate more time was needed for disinfection

– Isolated segment of main was flushed for 30 minutes

– Samples were taken again – chlorine residual was at normal value

– Line was placed back in service

Case Study: Lessons Learned

• Delaware needs more elevated storage! (2 MGD under construction)

• Delaware needs addition main lines (24” in design)

• Improve quality assurance on OUPS tickets• Work toward a GIS-based line and valve

mapping system

Case Study: Lessons Learned

• Work closely and early with OEPA during major events

• Reverse 911 automated calling works with about 80% effectiveness

• It is very helpful to have a previously calibrated water distribution model

The Advantages of a Calibrated Water Model

During (and Before) a Water Main Break

Dan Barr, PE

Burgess & Niple, Inc.

What Are the Advantages?

A calibrated water model can:• Determine the impact of a leak • Determine the impact of an out of service

main • Help decipher abnormal results from the

incident• Reinforce the system before a break

occurs

Determining the Impact of a Leak

To determine the impact of a leak:• Enter the leak into the model as a large

demand at the main break location• Use a variety of leak estimates to

determine the significance of the impact including fire flow analysis tools

Determining the Impact of a Leak (cont.)

To determine the impact of a leak:• Use the model to determine the lowest

pressures in the system – local and system-wide. Useful when determining boil alert locations

• If the leak can’t be isolated quickly, use the model to predict how the distribution system will perform under high leak demands over time

Determining the Impact of an Out-of-Service Main

This can be done by: • Closing the affected pipe in the model

• Running simulations over time to determine how

well the elevated storage tanks fill and drain.

After the main is isolated and the leakage stopped, the model can predict the system’s performance when the main is out of service.

Deciphering Abnormal Results from the Incident

• Locate unknown, previously closed valves

• Locate unknown pipe connections• Identify if valves are incorrectly closed• Discover multiple leaks

When the model results do not align with the field results, use the model to:

Optimizing the System Before a Break

• Complete the activities mentioned previously in advance

• Use results from trial runs and leak simulations to determine the best corrective actions

• Study the distribution system and identify/correct the weak points before a major break occurs

Summary

• Mistakes

• Lost water

• Customer boil alerts

Using calibrated water models during a water main break can minimize:

AnyQuestions?