An investigation of the potential environmental contamination from the leachate of the Rasht waste disposal site in Iran

This research deals with detecting the underground layer geometrics and conditions, probable faults and crushed zones, thickness of alluvium, determination of pollutant plume development, and groundwater quality in the study area. The Visual HELP and HYDRUS programs were used to evaluate hydrologic properties and contaminant transport, respectively. All required data which consisted of the geotechnical study (drilling the borehole and dug well), the geophysical study (geoelectrical sounding), and geochemical analysis of water and leachate samples were collected in the field operations. According to the results of ten years of hydrologic data evaluation of this site by using the Visual HELP program, the mean rate of leachate percolation from this site was equal to 1.095 m per year. From the interpretation of the vertical electrical resistivity soundings curves which was calibrated by the geotechnical borehole log, a four-layer geoelectrical model was recognized. These layers consisted of surface layer (loose and fine grained topsoil), medium grained alluvium, saturated layer, and high resistivity bedrock. The physico-chemical analysis of ten surface and groundwater sample indicated that these samples were not contaminated by leachate yet. Based on 1D, 2D and 3D modeling of contaminant transport using the HYDRUS 1D and the HYDRUS 2D/3D program, during the ten years of the onset of leachate seepage, contaminant plume migrated a short distance (<200 m) due to high compaction of fine grain sediments. In addition, the high compaction of a third layer (M3) in a depth of more than 40 m introduces a natural barrier to infiltration and movement of contaminant to the deep subsurface.