Improved Rating System for Hazard Assessment Related to Subsurface Migration of Landfill Gas from Municipal Solid Waste Landfills and Dumps

Abstract

Among the hazards from landfill gas (LFG), explosions due to methane migrated from municipal solid waste (MSW) sites have resulted in evacuation, property damage, and injuries and deaths for human beings. This study develops an improved rating system to assess the hazard for subsurface migration of LFG leading to explosion. The study first reviews the literature regarding subsurface migration of methane and identifies eight parameters important for the hazard: waste quantity (area and waste height), waste depth below ground and above the water table, waste composition (biodegradable fraction), annual rainfall, number of rainy days, soil permeability, distance to nearest receptor, and land use. Consequently, assessment of the only existing rating system, i.e., risk assessment for small closed landfills (RASCL), applicable to MSW sites for the hazard indicates that it gives equal ratings to sites with distinct characteristics because it uses only five of the eight parameters identified and uses improper ranges for four of the parameters. The RASCL is improved by introducing three kinds of modifications: modifying ratings for existing parameters, introducing ratings in the system for the three parameters, and adding a provision to account for uncertainty in the input data using fuzzy logic. The improved system, ExpRASCL, gives distinct rating scores when applied to MSW sites with continuously varying characteristics and performs better in sensitivity analysis. When applied to waste dumps (i.e., landfills without liner and cover) in Indian cities, ExpRASCL is able to categorize these waste dumps as low hazard, medium hazard, and very severe hazard and can help determine a closure alternative between a cover system with active gas collection system and a cover system only.