Site Characterization of Landfill using Soil gas, Hydrochemical and Geophysical Methods

To identify the effect of landfill waste for groundwater and unsaturated soil environment, the expedited site assessment, soil gas, geophysical prospecting, and in-situ chemical analysis of contaminants and indicators of pollution were executed. The aquifer of the study area is mainly composed of 8 to 10 m sandy sediment overlying Jurassic granite. The active sampling method was addressed to investigate the distribution of soil gas at the study area. The spatial distribution of soil gas at the depth of 80-100cm showed the boundary of buried waste and the biodegradation processes and the degree of waste decomposition. The CO2 and CH4 concentration across the disposed direction increased by the intensive decomposition of waste and this indicated the methanogenic condition of unsaturated zone of landfill. The geophysical survey at the municipal landfill was executed to delineate the size and extent of soil and groundwater contamination. The electromagnetic (EM), magnetic, and resistivity method were used for site investigation. From the EM method, we can get the information of soil conductivity directly related to the leachate of the contamination. The magnetic anomalies showed the boundary of landfill which was not identified on the surface due to soil capping. The results of geophysical survey were well matched to those of hydrogeochemical survey carried out inside and near the landfill. Electric conductivity (EC) of the groundwater sampled from low resistivity anomaly region of EM result was higher than background value and the border estimated from the magnetic survey showed good agreement with that estimated from the soil gas detection survey. The monitoring of electrical resistivity survey showed the leakage of leachate from landfill and this results well coincided with the groundwater chemistry. From the research results for groundwater quality, it was considered that the groundwater contamination by leachate from landfill is controlled by groundwater flow attributed by the original topography and liner.