Natural Gas Leaks in the District of Columbia

A report of trends, monitoring, and mitigation efforts on WGL’s natural gas distribution pipeline system
Updated September 2023



Increasing transparency and improving access to natural gas leak information and trends is a top priority for the DCPSC.  The Washington Gas Light Company (WGL) owns a 1,200-mile natural gas distribution pipeline system in the city which provides service to approximately 165,000 District customers. This leak information is beneficial to those ratepayers and other stakeholders. DCPSC staff closely monitor WGL’s natural gas leak trends, WGL’s ongoing gas leak survey and detection program, the company’s annual leak repair efforts, as well as its accelerated pipeline replacement program, PROJECTpipes. Trained and certified Commission staff continue to conduct pipeline safety and damage prevention inspections.

Natural gas leaks by occurrence and type

The Commission monitors WGL’s reporting of gas leaks to the Pipeline and Hazardous Materials Safety Administration (PHMSA). Federal authorities require gas operators to report leaks in two categories: “total” leaks and “hazardous” leaks. PHMSA defines a hazardous leak as one that represents an existing or probable hazard to persons or property and requires immediate repair or continuous action until the conditions are no longer hazardous.
There were a total of 1,260 gas leaks in 2022 in the District, representing a 12.7% decrease from 2021. About 969 of those leaks (77%) were deemed hazardous. 
Total gas leaks in 2022 were about 3.5% higher than 2017. The rate of increase in annual gas leaks appears to be slowing down since 2017; however, the DCPSC will continue to closely monitor this emerging trend to determine if this trend remains sustainable. There were fewer gas leaks in 2022 than in four of the past five years.

About 619 of the leaks occurred on “mains pipes,” which are distribution pipes that serve as a common source of supply for more than one customer line. About 641 gas leaks occurred on “service” line pipes, which are pipes that transport gas from a common source of supply to a customer.
Gas leaks that occur on private and/or customer-owned piping, appliances, and other equipment located “behind-the-meter” inside a commercial building or residence can be hazardous if undetected and not repaired immediately. These leaks often occur in confined spaces without adequate ventilation or other protections. It is the property owner and/or manager’s responsibility to properly maintain such equipment and piping within their property to further protect customer and public safety.  The gas leak tables noted below only cover gas leaks on WGL-owned piping and equipment. 

The tables below provide a comparison of gas leak data for calendar years 2017-2022, as reported to PHMSA. The category of “other” represents those gas leaks reported to PHMSA which are not deemed hazardous.

WGL Natural Gas Distribution System Leaks by Calendar Year for the District of Columbia

  2017 2018 2019 2020 2021 2022
Hazardous 263 454 511 385 449 390
Other 327 430 473 482 323 229
TOTAL 590 884 984 867 772 619

  2017 2018 2019 2020 2021 2022
Hazardous 494 596 629 493 570 579
Other 133 178 213 155 101 62
TOTAL 627 774 842 648 671 641
GRAND TOTAL 1,217 1,658 1,826 1,515 1,443 1,260
Difference from previous year           -12.7%
Cumulative difference from 2017           3.5%
WGL Natural Gas Distribution System Leak Rates by Calendar Year for the District of Columbia

Leaks per mile of main
  2017 2018 2019 2020 2021 2022
Hazardous 0.22 0.37 0.42 0.32 0.37 0.32
Other 0.27 0.35 0.39 0.39 0.27 0.19
TOTAL 0.49 0.73 0.80 0.71 0.63 0.51

Leaks per 1,000 services
  2017 2018 2019 2020 2021 2022
Hazardous 3.95 4.75 5.02 3.93 4.57 4.64
Other 1.06 1.42 1.70 1.24 0.81 0.50
TOTAL 5.02 6.17 6.72 5.17 5.38 5.14

Causes of natural gas leaks: 2017-2022

All leak root causes are identified and reported annually by WGL to PHMSA in accordance with federal regulations. According to data reported to PHMSA from 2017 to 2022, the most frequent leak causes are due to pipe, weld, or joint failure and corrosion.

Pipe, weld, or joint failure 59%
Natural forces 19%
Corrosion 17%
Excavation damage 4%
Incorrect operations 1%
Equipment failure <1%
Corrosion 40%
Pipe, weld, or joint failure 34%
Excavation damage 17%
Natural forces 4%
Incorrect operations 2%
Outside forces damage 2%
Equipment failure 1%

Natural Gas Quality of Service Standards (NGQSS)

In addition to monitoring WGL gas leak data reported to PHMSA, the DCPSC adopted Natural Gas Quality of Service Standards that requires WGL to provide, among other things, quarterly detailed leak reports, known as the Leak Identification, Detection, and Repair, and Odor Complaints report (LIDAROC). This report contains, among other things, a numeric grade for each leak, the type of leak, a location of leak (including the ward), the gas pressure involved, the number of customers affected, the cause of the leak, an estimated and actual time to repair the leak, and other actions taken. Leak reporting requirements to the DCPSC are more stringent and detailed than the summarized annual gas leak reporting provided by WGL to PHMSA. The DCPSC monitors WGL’s performance quarterly and annually.
All leaks reported to the DCPSC in the LIDAROC process are graded 1 through 3. A Grade 1 leak refers to a hazardous leak that presents an immediate or probable hazard to persons or property and requires immediate repair or continuous action until the conditions are no longer hazardous. A Grade 2 leak refers to a leak that is recognized as being non-hazardous at the time of detection, but requires scheduled repair based on probable future hazard. Grade 2 leaks are monitored and scheduled for repair, but do not require immediate action. A Grade 3 leak refers to a leak that is non-hazardous at the time of detection and can be reasonably expected to remain non-hazardous. Grade 3 leaks are monitored to ensure they do not worsen. Grade 1 and Grade 2 leaks reported to the Commission are generally included in the leaks reported to PHMSA. 

The DCPSC oversees WGL compliance with NGQSS and monitors the utility’s performance both quarterly and annually.

WGL activities
WGL undertakes extensive gas leak repair efforts every year, including emergency repairs. Annual leak repair expenses fluctuate based on the number and nature of the leaks as well as the magnitude of repairs needed.
WGL also has an ongoing level of normal replacement work. For example, the company invested $88 million over a recent 7-year period to include retiring about 12 miles of main and nearly 5,800 gas service lines in the District. WGL previously worked to fix vintage mechanical couplings, an approximately $75 million investment that covered 27 miles of gas main pipe, nearly 3,700 service lines, and 20,000 couplings. 

WGL also executes many accelerated pipe replacement programs (see below).
Leak survey and detection
In addition to responding to leak calls reported by the public, WGL conducts periodic leak survey activities throughout the District through six survey cycles according to the characteristics of the area and the piping systems present. Leakage surveys are systematic inspections used to locate any leaks in a gas piping system. A survey consists of testing and inspection of the area around the pipelines with gas detection equipment by a qualified technician. The entire distribution system is surveyed on a three-year cycle, exceeding the five-year minimum requirement outlined in federal regulations.
Piping description Leak survey cycle
Business districts Annual
Places of public assembly Annual
High-pressure transmission systems Six months or twice per year
Cast iron systems (above 1psig) Annual
Gas mains on structures in commercial districts Three months or four times per year
Gas mains on structures in non-commercial areas Six months or twice per year
NOTE: Mains on structures are WGL- owned pipes attached to structures such as buildings or bridges. This category does not include any customer-owned behind-the-meter piping.
The DCPSC previously approved a WGL Advanced Leak Detection (ALD) pilot program to review, test, and deploy ALD equipment and practices. The ALD program involves advanced vehicle-mounted sensing equipment. The DCPSC continues to monitor the evolution of this program.

DCPSC pipeline safety, damage prevention, and service quality activity

The DCPSC Office of Compliance and Enforcement (OCE) coordinates pipeline safety and damage prevention efforts for the Commission which complement federal laws and regulations governing gas pipeline safety, damage prevention, and pipeline operations, maintenance, and construction. OCE staff include PHMSA-trained and certified inspectors whose certifications are continually updated through on-going pipeline safety courses. OCE continuously conducts pipeline safety inspections — in a 12-month period in 2022-2023, OCE executed nearly 400 pipeline safety inspections and more than 700 damage prevention inspections. 
OCE also monitors gas pipeline damage incidents caused by excavation activity in the District. WGL experienced 130 gas pipeline damage incidents in 2022 in DC, representing about a 9% reduction from 2017 incidents, despite higher levels of excavation.
OCE may propose monetary and non-monetary compliance and enforcement actions if necessary for WGL to comply with federal and District laws and regulations. Monetary penalties serve as a deterrent to future violations and unsafe practices and are not recovered in utility rates. The DCPSC pipeline safety and damage prevention efforts are audited annually by PHMSA and the U.S. Department of Transportation. The DCPSC has received eight consecutive 100% scores on PHMSA annual audits from 2015-2022.

PROJECTpipes is WGL’s accelerated pipeline replacement program to modernize the natural gas distribution system in the District and enhance overall system safety, reliability, and resiliency for gas customers. This program helps the District meet its climate goals by reducing potential leaks and methane gas emissions on the distribution system. WGL estimates that the total reduction in greenhouse gas (GHG) emissions from 2021-2023 will be approximately 6,000 metric tons of CO2e. The DCPSC estimates that this project will help avoid more than 100 leaks in that timeframe.

WGL has replaced or remediated 33.1 miles of high-risk gas main and 6,529 service lines through the PROJECTpipes program as of Dec. 31, 2022.


Commission staff will periodically update this gas leak data and other relevant information with the latest annual information reported by WGL.