The New Mexico Environment Department has accepted the 2016-2017 report on the Los Alamos County Airport evapotranspiration landfill cover, which states that the cover is in excellent condition and is performing as designed.
The report, prepared by Stephen F. Dwyer of Dwyer Engineering, LLC., indicated that there was no methane emission and no water percolation through the cover into the underlying waste but rather that moisture is migrating upward from the waste. Dwyer also noted that vegetation cover is maturing and that there are no signs of significant degradation or settlement.
From 1943 to 1973 household refuse from the Los Alamos townsite and office trash from Los Alamos National Laboratory was placed at the airport site and in 1984, waste excavated from the western portion of the County landfill to the east was placed in the debris disposal area.
In 2007, asphalt and concrete hangar pads were placed to allow for the expansion of airport hangar facilities, but in from 2009 to 2012, inspections identified significant problems with the site and the new cover. The issues included more than two feet of differential settlement, elevated methane gas levels, surface cracking, ponding, poor surface drainage and signs that water was infiltrating into the underlying waste through cracks in the asphalt. In 2011, elevated methane levels at the landfill reached 100 percent of the lower explosive limit.
Remediation began in 2015 with the removal of the asphalt cover and the concrete hangar pads followed by relocation of waste from the western portion to within the remaining footprint of the landfill and replacement of the concrete hangar pads. The new vegetated soil cover system was then installed.
Dwyer also inspected the storm water control system, fencing, retaining walls, erosion and sedimentation control measures and site access. Landfills regulated under the Resource Conservation and Recovery Act are subject to monitoring for 30 years after their closure, however that time period can be reduced or increased dependent on findings, the integrity of the closure and agreements by applicable officials and regulators.