Shared Action Plan: Annual Results
This report documents the progress of a first-in-the-nation shared action plan involving gas utilities identifying and repairing distribution system leaks with the largest environmental impact. HEET’s role is to independently verify results and make recommendations to utilities for improvement.
Massachusetts has some of the oldest natural gas infrastructure in the country.1 Old pipes in this system are leaking methane, a greenhouse gas 86 times more potent than carbon dioxide over the first 20 years in the atmosphere.2 The cost of this wasted gas is passed on to customers and is estimated to be millions of dollars per year.3 Methane from gas leaks also poses a safety hazard to both people and vegetation.
Research in 2016 showed that just 7% of the Metro Boston distribution system leaks emit half of all the gas by volume, creating a clear policy opportunity.4 Later the same year, the Massachusetts Legislature enacted a law requiring that these leaks of significant environmental impact (‘SEIs’) be repaired, since doing so would cut methane emissions in half for the least cost to the utilities and the least disruption to cities and towns. Gas companies had always been mandated to focus on the potential hazardousness of a leak and not emissions, and had no reliable and accurate method to identify SEIs. In 2017, HEET coordinated a large collaborative study to determine a new SEI identification method. Working with Eversource Gas of Massachusetts (formerly Columbia Gas, and now a part of Eversource Energy), and National Grid, Gas Safety Inc., Mothers Out Front and other stakeholders, the research team field-tested multiple methods and showed that a new leak identification protocol - the ‘leak extent method’ - is a quick, effective and low cost solution.6 The shared action plan emerged from this collaboration.
Since 2018, National Grid and Eversource Gas have been using the leak extent method to identify SEIs and prioritize them for repair. Based on the testing of hundreds of SEIs by HEET since the beginning of the program, utility SEI identification rate appears to be improving in accuracy over time.
Note: Regulations require that SEI leaks are repaired within 1-3 years of identification, depending on the extent and repair method. Emissions reductions are therefore expected to trail identification by 1-3 years.
The annual estimated impact of all SEIs based on the 20 year global warming potential of methane is currently equivalent to approximately 3% of Massachusetts’s greenhouse gas inventory, which is equivalent to the emissions of 1/3rd of all Massachusetts stores and businesses (i.e. the commercial sector) in 2017.7
Massachusetts is the first to enact legislation to identify SEIs, the first to determine an SEI identification protocol, and the first to test it widely in the field across multiple gas companies. We hope to report in coming years, when repairs of currently identified SEIs are confirmed completed, that we are also first in the nation to cut in half our methane emissions from the gas distribution system. This shared action plan work will continue to provide independent analysis, findings and assistance to utilities to help improve over time.
1. Pipeline and Hazardous Materials Safety Administration, Gas Distribution Annual Data, 2020
2. IPCC Climate Change Report, Climate Change 2013: The Physical Science Basis, p714, Table 8.7
3. See Appendix 4, Annual Total Cost from the Distribution System for more information
4. Hendrick et al, 2016, Fugitive methane emissions from leak-prone natural gas distribution infrastructure in urban environments
5. Originally suggested by Gas Safety Inc., Appendix 2
6. Zeyneb Magavi, Robert Ackley, Margaret Cherne-Hendrick, Dominic Nicholas, Eddie Salgado, Audrey Schulman, Jason Taylor, Nathan G. Phillips, Identification of Large Volume Leaks in Natural Gas Distribution System, publication pending
7. See Appendix 6, Calculating The Greenhouse Gas Emissions of SEIs
- National Grid, Eversource Energy and Eversource Gas of Massachusetts used the leak extent method to identify SEIs.
- In 2020, Massachusetts gas utilities reported 24,243 leaks, half of which were found that year, the other half were carried forward from previous years.
- Reported Rates of SEIs: Based on 2020 quarterly leak inventory reports to the DPU, National Grid, Eversource Energy and Eversource Gas of Massachusetts reported lower rates of SEIs compared to what we expected: 5.42%, 2.17% and 2.23% respectively. We recommend utilities adjust the SEI definition threshold to eliminate the largest 7% of leaks in any non-hazardous repair prioritization. This approach would allow those utilities that have eliminated a significant portion of their largest SEIs already to continue to capture half of the total emissions no matter the population of leaks.
- Accuracy of Identification: HEET sampled and studied 96 utility-identified SEIs this year to check that the leak extent method was being applied consistently. The utilities still appear to be over-identifying SEIs. National Grid improved, over identifying by only 60%, compared to 100% last year. Eversource Gas of Massachusetts over-identified by a factor of 4 compared to 3 last year. Eversource Energy only slightly over-identified by 10%. Given the over-identification tendency, the actual SEI rates may be lower than those reported.
- National Grid’s measured SEI extents were 40% less on average than HEET’s confirmed extents. This appears to indicate a strong response from surveyors to the information we provided last year when they were measuring on average larger by a factor of 5. Eversource Gas of Massachusetts measured SEI extents twice as large on average as HEET’s confirmed extents, which was about the same as last year. Eversource Energy SEI extents were very close to HEET’s confirmed extents. HEET remains ready to meet with surveyors to assist through observation and training. HEET’s assistance is free to gas utilities, including their subcontractors, and can potentially help utilities reduce emissions.
- Of the confirmed SEIs, whilst there were differences between HEET’s and utilities’ leak extent measurements, these differences didn’t result in any significant re-grading that would have required a change of repair scheduling or prioritization.
- Missed SEIs: HEET ran a mobile gas leak survey with a Cavity Ring Down Spectrometer (CRDS) and identified twice as many leaks as were currently reported by the utilities in their quarterly leak reports. Given this, it is possible that there are twice as many SEIs out there as the utilities have identified.
- Repair Rates: SEI repairs are not always successful. They appear to eliminate all gas from the entire leak footprint only 1/4 of the time. Most of the unsuccessful repairs occurred on cast iron pipe and thus could be from multiple leaks in one leak extent.
- FluxBar: The FluxBar is a tool that allows gas companies to compare the emissions of leaks. Whilst we had limited FluxBar data, National Grid showed an improved use of the tool and successfully measured leak flux, thus providing a path to confirmed methane reduction. No strong correlation between calculated steady state leak flux and reported leak extent was found in the six flux measures, nor were any of the six leak extent measurements confirmed by HEET. More study is required.
- CRDS: The cavity ringdown spectrometer continues to be an excellent tool for finding new potential gas leaks.
