This study presents an approach for estimating and monitoring methane emissions from an active landfill using both: (a) in-situ near-surface mobile atmospheric CH4 mole fraction measurements, and (b) complementary measurements from sniffing campaigns mainly dedicated to the identification of sources and an analysis of the CH4 mole fractions measurements made on the landfill perimeter. The study also estimates the total emissions from the landfill using a simple atmospheric inversion approach based on a Gaussian plume dispersion model. Even though this study focuses on only one landfill site in France, the measurement techniques and tools presented herein contribute to the field of landfills methane emission estimations and monitoring. The manuscript was reviewed by two expert reviewers, following which the authors addressed the reviewers' comments and submitted a revised version for publication in AMT.