Abstract

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 °F), and above the Higher Operating Value (140 °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 ½ to 3 years, depending on the well.

摘要

通常认为垃圾填埋场至少经历四个分解阶段，1) 初始需氧阶段，2) 厌氧酸阶段，3) 初始产甲烷阶段，和 4) 稳定产甲烷阶段。虽然垃圾填埋场火灾很常见，但最近已经认识到缺氧地下加热事件 (ASHE)，可能由铝废料催化。本文回顾了两个这样的事件，以法医检查在 ASHE 发生之前气体记录中是否存在可预测的早期预警信号，以促进早期行动。在俄亥俄州东斯巴达的县级回收和处置设施中，减少甲烷（CH ₄) 在尸检分析中被确定为异常垃圾填埋条件的早期指示参数 (IP)，因为 ASHE 抑制了产生甲烷的微生物。在这里，CH ₄ :CO ₂比率也至少在一些气井的成熟 ASHE 开始前一年降至 < 0.8。垃圾填埋场 A 是一个城市固体废物填埋场，运营至 2004 年 12 月。垃圾填埋场气体和温度分布在关闭后直到 2009 年都正常，当时几口井的填埋气体特征开始向不稳定状态演变，甲烷减少（CH ₄ <43 %)、增加一氧化碳 (CO > 500 ppm)、增加平衡气体 (>20%) 和 CH ₄ /CO ₂比率下降到 0.8 以下。ASHE IP 序列的演变是，1) CH ₄下降，随后，2) CO ₂和平衡气体百分比增加，然后 3) 在 ASHE 开始前 CO。随后，4) 渗滤液量增加，5) BOD/COD 比率和渗滤液中的苯，最后 6) 垃圾填埋场污染物向地下水的释放。这些多条证据表明，运营商应仔细评估数据趋势，将其作为潜在异常条件的指标。许多垃圾填埋场 A 气井的气体分布与县范围内的相似，并且似乎可以通过基于温度、CO ₂和 CH _{4的垃圾填埋场火灾指数 (LFI) 进行预测}模式。虽然在一些井中偶尔出现超过 NSPS 温度 (131°F) 和高于较高操作值 (140°F) 的情况，但垃圾填埋气 IP 特征和 LFI 的变化似乎早于主要热事件½ 到 3 年，具体取决于井。