Subtle early-warning indicators of landfill subsurface thermal events

It is generally accepted that landfills undergo at least four phases of decomposition, 1) an initial aerobic phase, 2) an anaerobic acid phase, 3) an initial methanogenic phase, and 4) a stable methanogenic phase. While landfill fires are common, recently anoxic subsurface heating events (ASHEs) have been recognized, potentially catalyzed by aluminum waste. This paper reviews two such events to forensically examine if there are predictable early warning signs in the gas record prior to the onset of an ASHE that could facilitate early action. At the Countywide Recycling and Disposal Facility in East Sparta, Ohio, decreasing methane (CH4) in landfill gas was identified in a post-mortem analysis as an early indicator parameter (IP) of an abnormal landfill condition because the ASHE inhibited methane-producing microorganisms. Here the CH4:CO2 ratios also decreased to < 0.8 at least one year prior to onset of the full-fledged ASHE in some gas wells. Landfill A was a municipal solid waste landfill that operated through December 2004. The landfill gas and temperature profiles appeared normal after closure until 2009, when landfill gas characteristics in several wells started to evolve toward an upset condition, with decreasing methane (CH4 <43%), increasing carbon monoxide (CO > 500 ppm), increasing balance gas (>20%) and a CH4/CO2 ratio decreasing below 0.8. The evolution in sequencing of ASHE IPs was, 1) declining CH4, followed by, 2) increasing CO2 and % balance gas and, then 3) CO before onset of the ASHE. Subsequently, 4) leachate volumes increased as did, 5) the BOD/COD ratios and benzene in leachate, and finally 6) release of landfill contaminants to groundwater. These multiple lines of evidence suggest that operators should carefully evaluate data trends as indicators of potential upset conditions. The gas profiles in many Landfill A gas wells were similar to those at Countywide and appear to be predictable by a Landfill Fire Index (LFI) based on temperature, CO2 and CH4 patterns. While there were sporadic exceedances of the NSPS temperature (131 degrees F), and above the Higher Operating Value (140 degrees F) in some wells, the change in landfill gas IP signature and the LFI appears to have pre-dated the major thermal event by between 1/2 to 3 years, depending on the well.