SEISMIC VELOCITY ANALYSIS TO DETERMINE MOISTURE DISTRIBUTION IN A BIOREACTOR LANDFILL

摘要

To establish an effective leachate recirculation process, the moisture distribution within a landfill must first be estimated so that leachate can be added appropriately to create optimal and homogeneous moisture conditions throughout the waste mass. Seismic surveys were conducted at a bioreactor landfill in Ste-Sophie, Quebec, Canada, with the objective of mapping the moisture distribution using seismic data collected from the surface of the landfill. Analysis of the travel times of direct and refracted seismic waves established that the landfill is structured as a 4.5 m upper layer of loose waste and a 25.5 m lower layer of compacted waste with average compressional wave velocities of 280 m/s and 380 m/s, respectively. Seismic velocity analyses indicated that an increase in moisture content, caused by leachate injection, increased the compressional wave velocity of waste. Specifically, the injection of approximately 1m~3 of leachate per meter length of trench through two recirculation trenches caused an increase on the order of 22 m/s (7 %) in the stacking velocity of the compressional waves reflected off the landfill bottom. The lateral radius of influence of the injected leachate was 5 m-10 m and the velocity results reached steady state approximately 3 hours after the injection ceased.