Time series analysis of performance data from closed landfills to forecast post closure monitoring needs

A landfill is considered functionally stable when it no longer presents an unacceptable threat to human health and the environment. Landfill stability depends on factors which include variables that relate to operations both before and after the closure of a landfill cell. Therefore, post closure period (PCC) decisions should be based on operational factors, design factors and post-closure performance data. The question of appropriate PCC period for landfills requires in-depth case studies focusing on the analysis of the performance data from closed landfills. In this study the performance data from a closed case study landfill was evaluated to forecast the level of stability of a landfill in terms of leachate and gas generation rates and quality. The data was analyzed by time series decomposition technique since seasonality in graphs was identified by regularly spaced peaks and troughs. The data clearly showed the general trend and provided a clear forecast for future planning purposes. Decreasing trends were seen for leachate quantity, landfill gas and methane, chloride, sodium, total dissolved solids, vinyl chloride,1,4-dichlorobenzene, chlorobenzene, xylenes, ethylbenzene, toluene, total BTEX and cis-1,2-dichloroethylene. Increasing trends were seen for iron and bicarbonate. Steady trends were seen for pH, ammonia and benzene. Based on these results, PCC monitoring needs identified for closed case study landfill.