Methane emissions have traditionally been assessed using on-site emissions measurements, occasionally coupled with simultaneous, full-facility estimates using downwind methods. A key aspect of these on-site studies was the presence of on-site sta who could observe and log the operational state of the facility during measurement. Maintenance events that occurred during measurement were typically logged, and measurements were adjusted for the maintenance activity or treated separately in data sets. As a result, on-site studies generally control for emissions from maintenance activities.