Annually, ~ 3.6 million abandoned oil and gas wells in the U.S. emit a combined ~ 3.2 Tg methane (CH4), adversely affecting climate and regional air quality. However, these estimates depend on emission factors derived from inventorying sub-populations of wells, but which vary by orders of magnitude due to inadequate sampling numbers. This problem is exacerbated by regional differences requiring independent emission inventories and the recent identification of poorly characterized super-emitters that skew the distribution. Currently, U.S. funding to remediate orphaned wells lacks standardized quantification methods needed to both prioritize plugging and account for emission reductions. Sensitive, reliable, affordable, and scalable CH4 flux quantification methods are needed. We evaluate a simple Gaussian plume method constrained by in situ ground measurements of CH4 concentrations and winds to estimate the leak rate from an orphan well in the Permian basin. We derive a flux of 10.53 ± 1.16 kg CH4 h-1 during a venting procedure that agrees with the directly measured volumetric flow rate of 9.0 ± 0.25 kg CH4 h-1. This is 71% greater than the flux measured 7-months prior which induces a bias between bottom-up and top-down estimates. Additionally, we discovered a secondary leak through the surface-casing inferred as 0.43-0.67 kg CH4 h-1 by both our ground Gaussian analysis and by transecting the plume with an uncrewed aerial system (UAS). Our technique addresses operational needs by reducing sampling time of leak detection and quantification and good sensitivity to characterize wells emitting below the detection limit of satellites.