Flow and Transport of Methane from Leaking Underground Pipelines: Effects of Soil Surface Conditions and Implications for Natural Gas Leak Classification

Reducing methane (CH4) emissions from natural
gas (NG)
pipeline leaks is crucial to minimize global warming while also providing
key safety benefits to communities. What is not well understood about
pipeline leak scenarios is the impact of different soil surface conditions
on the belowground leak transport behavior and subsequently the NG
leak classification. In this study, we conducted a series of controlled
leak experiments, varying based on the surface conditions including
snow, moist soil layers, asphalt, and grass. Data indicated that temporary
rain and snow surface cover conditions result in CH4 concentrations
extending 3 times further than the equivalent leak scenario under
dry soil conditions, resulting in levels that pose heightened environmental
and safety risks. Furthermore, after leak termination, CH4 trapped under snow, moist soil, and asphalt surface conditions persisted
for up to ∼12 days, with 5–15% CH4 (v/v)
conditions persisting underground for 7.5 days. Even after leak termination,
NG continued to migrate laterally away from the leak source, extending
the plume boundary by 2–4%. While efforts to study a wider
range of environmental conditions are underway, the findings of this
study provide crucial insight into identifying and prioritizing leaks
from the perspectives of both safety and the environment.