Gas Infrastructure Audit

Like many towns in Massachusetts, Weston has a gas leak problem due to the state’s aging gas infrastructure, which is the second oldest in the country. At the end of 2017, National Grid, Weston’s gas service provider, reported 141 unrepaired gas leaks in town, some of which were over 20 years old. 

Not only are gas leaks a safety concern, but they are also an environmental and health issue for our community. Methane is 86-times more potent as a greenhouse gas than carbon dioxide over the first 20 years in the atmosphere, contributing significantly to the climate crisis. 

With the support of the Town's newly established Sustainability Committee, the local citizens' group, Sustainable Weston Action Group (SWAG), approached the Board of Selectmen with a request for the Town to conduct an independent audit of its gas infrastructure in order to better understand its full condition.

Understanding Leak Grades and Repairs

National Grid prioritizes gas leak repairs through a classification of three grades:

  • Grade 1 - typically located in densely populated or high traffic areas - these are fixed immediately
  • Grade 2 - considered not to be of immediate risk to life or property, but potentially may become hazardous - these are prioritized for repair
  • Grade 3 - deemed non-hazardous to life or property - not prioritized for repair

All of Weston's 141 unrepaired leaks, as reported by National Grid by December 2018 and classified according to gas company standards, are Grade 3 leaks. However, the grading system does not take into account the size of the leak or the amount of methane being emitted. Further, Weston has higher pressure pipes at 60 psi, compared to other communities such as Lawrence or Boston at 0.5 psi, and many of the pipes are made out of corroding cast iron or bare steel.

Leak Survey and Audit

Phase 1

In February of 2019, the Board of Selectmen approved Phase 1 of the audit, which aimed to survey the town’s road network and locate all elevated methane levels.

Phase 2

The survey was completed in April and showed that there are 66% more leak locations than reported by National Grid at the end of 2018. Members of SWAG and Gas Safety Inc. presented Phase 1 survey results in May and requested the Board of Selectmen approve Phase 2 of the audit, which would conduct a full assessment of all elevated methane locations, confirming the source and size of the leak, and document any existing or potential damage to surrounding vegetation and trees.

Final Report

Below is an interactive map showing the location of all unrepaired gas leaks in Weston confirmed in the Audit. Click on a leak location pin to get more information about that leak including the exact location, date reported, leak size, trees impacted, and a link to a detailed sketch of the leak extent.

Regular leaks = leaks that measure <2,000 square feet

Large volume leaks (SEIs) = Significant Environmental Impact leaks according to the Mass. Department of Public Utilities regulation, measuring 2,000 square feet or more

The map above is an interactive summary, created from the following information:

The map was created by HEET - Home Energy Efficiency Team - a non-profit organization in Massachusetts working to improve energy efficiency in homes and communities across the state. See more at

Audit Results

The results of the Final Audit (above) confirm the gas leak problem in Weston is worse than reported:

  • December 2017: National Grid reported 141 Grade 3 unrepaired gas leaks
  • December 2018 National Grid reported 175 Grade 3 unrepaired gas leaks
  • June 2019 Weston Gas Infrastructure Audit confirmed 295 unrepaired gas leaks:
    • 102 leaks were measured at 2,000 sq. ft. or more* 
    • 166 leaks were misclassified: 2 leaks were identified as Grade 1 leaks for immediate repair; 164 leaks were identified as Grade 2 leaks, as the gas leak had already or was at risk of causing damage to property, including trees, shrubs, and lawns
    • A total of 325 trees were identified as either already compromised or at risk, due to their location in the gas leak zone

SWAG prepared a one-page summary of the Gas Audit Analysis (PDF) for download.

* Under new Department of Public Utilities (DPU) ruling, these are classified as “Significant Environmental Impact” leaks (SEI). In Massachusetts, the average percentage of known leaks classified as SEI for a community is 5-7%. In Weston, 35% of the leaks are SEI classified. Two of those are exceptionally large at over 10,000 sq. ft.

Benefits to Weston

As a result of the Gas Infrastructure Audit, the Town of Weston benefits in four key ways:

  1. The accurate map of all current gas leaks – location, size, and condition – can be used as input into a repair and maintenance strategy working with our gas service provider National Grid.
  2. The misclassified gas leaks can be expedited for repair
  3. All “Significant Environmental Impact” leaks will be prioritized for repair within 12 months to 2 years under new DPU regulations. This will positively impact Weston’s greenhouse gas footprint.
  4. Any investment in green infrastructure, like planting trees in the Town Center redesign project, or maintaining your private landscape, can be evaluated for any potential gas leak issues.

In addition, members of the Sustainable Weston Action Group, have shared the results of the audit with other communities, are working with local non-profits to integrate our data into state-wide research on greenhouse gas emissions, and testified at a DPU hearing on the measurement of lost and unaccounted-for gas.

Public Forum - Natural Gas: Triage and Transition

Members of Sustainable Weston Action Group met with the Board of Selectmen in September to discuss the final audit report and the next steps. In addition, a public forum was held in October, "Natural Gas: Triage and Transition" to discuss the impact of leaking gas infrastructure across Massachusetts, and propose both short term and longer-term solutions. 

Department of Public Utilities Public Hearing

Members of SWAG attended and provided testimony during a public hearing in June 2019 on establishing requirements for Uniform Reporting of Lost and Unaccounted-for Gas. Testimony focused on the process taken to understand the town's gas infrastructure, highlighting the need for increased regulation of gas leak measurement, maintenance, and management. 

Weston's representation was also joined by representatives from the Attorney General's Office, Conservation Law Foundation, Sierra Club, Home Energy Efficiency Team, Mothers Out Front, Emerald Necklace Foundation, and the communities of Boston, Brookline, Cambridge, Wellesley, and Salem. DPU will have until the end of the year to provide its final ruling.