a sidewalk in a wall-to-wall paved area that does not qualify as a Grade 1 leak. Any reading of 100% LEL, or greater, under a street in a wall-to-wall paved area that has significant gas migration and does not qualify as a Grade 1 leak. Any reading less than 80% LEL in small substructures (other than gas associated substructures) from which gas would likely migrate creating a probable future hazard. Any reading between 20% LEL and 80% LEL in a confined space. Any reading on a pipeline operating at 30 percent specified minimum yield strength (SMYS) or greater, in a class 3 or 4 location, which does not qualify as a Grade 1 leak. Any reading of 80% LEL, or greater, in gas associated sub-structures. Any leak which, in the judgment of operating personnel at the scene, is of sufficient magnitude to justify scheduled repair. A Grade 3 leak is non-hazardous at the time of detection and can be reasonably expected to remain non-hazardous. Examples of a Grade 3 Leak are: Any reading of less than 80% LEL in small gas associated substructures. Any reading under a street in areas without wall-to-wall paving where it is unlikely the gas could migrate to the out-side wall of a building. Any reading of less than 20% LEL in a confined space. Studies In 2012, Boston University professor Nathan Phillips and his students drove along all of Boston roads with a gas sensor, identifying 3300 leaks. The Conservation Law Foundation produced a map showing around 4000 leaks reported to the Massachusetts Department of Public Utilities. In July 2014, the Environmental Defense Fund released an interactive online map based on gas sensors attached to three mapping cars which already were being driven along Boston streets to update Google Earth Street View. This survey differed from the previous studies in that an estimate of leak severity was produced, rather than just leak detection. This map should help the gas utility to prioritize leak repairs, as well as raising public awareness of the problem. In 2017, Rhode Island released an estimated 15.7 million metric tons of greenhouse gases, about a third of which comes from leaks in natural gas pipes. This figure, published in 2019, was calculated based on an assumed leakage rate of 2.7% (as that is the rate of leakage in the nearby city of Boston). The study's authors estimated that fixing the leaks