Health Stream Article - Issue 58 - June 2010

Boston Main Break

A break in major water supply pipeline serving the U.S. city of Boston has resulted in a boil water alert being issued for almost 2 million people. Water supplies to 30 communities were affected when a steel connector joining two sections of pipe failed at around 9.30 am on Saturday 1 May. The 10-foot (3 metre) diameter pipe connects the 7-year old MetroWest Water supply tunnel and the older City Tunnel, and provides the main water supply to Boston and a number of other communities. The leaking water quickly forced its way to the surface, creating a small lake and washing away a section of a nearby road before draining into the Charles River. It was estimated that up to 8 million gallons (30 ML) of water was being lost per hour before the broken pipe section was isolated for repairs.

The Massachusetts Water Resources Authority (MWRA) initiated emergency response procedures as soon as the leak was detected by an automated alarm system and visually confirmed by security cameras. The initial assessment resulted in a decision not to immediately close down water flow through the ruptured pipe as this could have created significant operational difficulties including loss of back pressure needed to start a pump station and intrusion of air into the water supply system, as well as loss of supply to downstream communities. Instead, flow through the break site was continued for several hours until arrangements were put in place to redirect water through alternative pipelines. Communities which had access to independent local water supplies were also contacted and asked to decrease withdrawals from the MWRA water supply system wherever possible.

By late Saturday afternoon, MWRA had succeeded in redirecting 90% of the usual MetroWest Water supply tunnel flow through alternative routes to bypass the break. To maintain adequate pressure, it was also necessary to bring on-line an emergency supply from an open reservoir via an old brick aqueduct which had been unused for decades. No water quality testing had been conducted recently on this water source and although it was chlorinated before introduction to the pipe network, there was a potential risk that protozoal pathogens such as Giardia or Cryptosporidium might still be present. In view of this uncertainty, it was considered necessary to issue a boil water notice for the 30 affected communities, including part of the city of Boston. Householders and businesses were advised that tap water could be used for bathing, toilet flushing and fire fighting but boiled or bottled water should be used for drinking, cooking, food preparation and tooth brushing. The State Governor also declared a state of emergency for the area affected by the main break.

The broken section of pipe was isolated and shut down approximately 9 hours after the break was detected, and the flooded area was then drained to allow inspection of the pipe. Initial fears that the emergency might last for several weeks if the pipe sections needed to be replaced proved to be unfounded, and it was decided that repair of the break using a steel collar would be possible. Fortunately, a suitable steel collar and heavy construction equipment was immediately available from a nearby major pipeline rehabilitation project being undertaken by MWRA. Working around the clock, MWRA staff and contractors were able to complete the repair by 4 am on Monday 3 May. The repaired section was then filled, pressure tested and disinfected before being brought back on-line at 5.30 am the same day.

While the repair work was still being undertaken, MWRA and the Massachusetts Department of Environmental Protection developed a water quality testing program and agreed criteria for ending the boil water notice following restoration of normal water supply. An intensive water testing program comprising approximately 400 samples per sampling round and two sampling rounds per day was agreed, with samples to be tested for total coliforms, E. coli and free chlorine residual. Two consecutive sampling rounds conducted approximately 8 hours apart with clear results would be considered satisfactory for lifting the boil water notice.

The affected communities were contacted early on Sunday morning and asked to conduct water sampling according to this program with the results of the second round of tests being received in the early hours of Tuesday morning. The boil water notice was lifted for all 30 communities by 7 am on Tuesday 4 May, some 59 hours after it had been declared. Homeowners and businesses were provided with advice on flushing water lines and water-using equipment within premises before resuming normal water use.

The incident highlighted the risks of lack of redundancy for major water supply lines. This risk had already been recognised by MWRA when the MetroWest Water Supply Tunnel was built and commissioned in 2003 to provide a more reliable alternative to the leaking Hultman Aqueduct. The 70-year old Aqueduct was then taken out of service in order to undertake an extensive rehabilitation program to restore it to serviceable condition and install new interconnections with the MetroWest Tunnel. This will provide complete redundancy for Boston's main water supply pipeline and allow failures in one pipeline to be easily bypassed by using the other pipeline. However until the project is completed in 2014, the water supply system is heavily reliant on the MetroWest Tunnel. A major failure in the new tunnel only seven years after commissioning was an unexpected event, but nevertheless one that had been included in MWRA's disaster planning program. This preparation, and a certain amount of good fortune, allowed a rapid response to the incident and restoration of normal water supplies in less than three days.

MWRA is now reviewing the Hultman Aqueduct rehabilitation program to determine whether staging of the project can be revised to bring the completion date forward without disrupting supply to consumers or running unacceptable risks associated with sections being out of service. In addition, pieces of the failed coupling recovered from the Charles River will be subjected to forensic examination in an attempt to pinpoint the cause of the failure. MWRA has also reviewed 28 other construction projects to identify any where pipeline couplings of the same or similar type were used. Eight projects were identified as having couplings of similar although not identical type. These projects will be subjected to risk assessments to evaluate failure risks in the light of findings from the investigation of this incident.

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