The problem of solid waste disposal becomes a serious problem of environmental concerns because most solid waste is disposed either by open dumping or sanitary landfill. This can badly affect the environment if landfill leachate contaminate soil or water resources. The increasing of population, human activities, and city expansion make a deficit for selecting potential areas for landfill in the future. This study has extended a landfill selection technique by incorporating geological characteristics of groundwater percolation into the analysis. Firstly, the calculation of area required for solid waste disposal in the next 20 years was carried out. This was done under the scenarios of maximum, mean, and minimum population growth rates. Then, GIS was used to analyze suitability of areas for solid waste disposal. The selecting criteria included slope terrain, surface water, groundwater, geological features, flood prone areas, community areas, land use, and transportation. The identification of landfill area was conducted by positive/negative- mapping. For the positive map, information on geological barrier, which was introduced in this study, was considered as a natural prevention of groundwater contamination from landfill leachate. The study found that from 7,400 km[superscript 2] of the study area, 106 km[superscript 2] are highly suitable candidate for waste disposal. The 5 five biggest patches of these high suitability areas, are in Tambon Khlong Hoi Khong, Tambon Thung Mo, and Tambon Samnak Kham. They are situated in the western part of Songkhla with area of 10.114 9.916 6.282 3.610 and2.997 km[superscript 2], respectively.
