An airborne survey on Aug. 15, 2021 detected two methane plumes over the landfill, months before Mill Seat was first required to scan its surface for methane.
Methane plumes: Carbon Mapper, from the Global Airborne Observatory aircraft survey of Aug. 15, 2021 (plumes GAO20210815t133815p0000-A and -B). Plume A’s emission rate is Carbon Mapper’s estimate; no rate was estimated for plume B, and no wind data was reported for the flight. Plume colours are adapted from Carbon Mapper’s plume images (light = less methane, dark red = more).
Timeline: GHD, Mill Seat Landfill 2021 Annual Compliance Certification and July–December 2021 Semiannual Monitoring Report (Jan. 30, 2022): the 2020 annual NMOC report, submitted Feb. 8, 2021, showed uncontrolled NMOC emissions above the 34 megagrams per year limit in NSPS Subpart XXX, and the gas collection design plan was submitted Dec. 31, 2021. Both 2021 semiannual reports state that Subpart XXX’s operational provisions did not yet apply. First surface scan: GHD, Mill Seat Landfill First Quarter 2022 Surface Emissions Monitoring Report (May 4, 2022).
A plume shows methane in the air at the moment of the flight; it does not by itself show exactly where on the ground a leak is.
Base map: Esri World Imagery; image dates vary. Exhibit: Full Circle Future.
Plume A: 187 ± 125 kg of methane an hour. Plume B: rate not estimated.