Impact of Remedial Landfill Cover Systems and Gas Extraction Systems on Groundwater VOC Concentrations

Volatile organic compounds (VOCs) are present in groundwater downgradient of many unlined landfills. Cover systems and gas extraction systems are often installed as remedial measures to decrease VOC concentrations. This paper examines the mechanisms by which non-aqueous phase liquids (NAPLs) placed within the waste fill may contaminate groundwater, and the potential effect of covers and gas extraction systems on these mechanisms. Field data from three case studies where covers and gas extraction systems were installed are presented. Although more data is needed to quantify the performance of these systems, three main hypotheses are presented. (1) Covers alone have a limited effect on VOC concentrations in groundwater. (2) Gas extraction systems may have spatially variable beneficial effects on VOC concentrations in groundwater. (3) The reduction of VOC concentrations due to gas extraction is likely to be a transient effect, i.e., if the gas extraction system is shut off, concentrations could rebound.