In Taiwan most of the waste landfills are built on the hillsides. Since the size of the sites is usually less than 10 hectares, they are regulated only by ”the Guide of Waste Landfills Placement” required by the Environmental Protection Agency of the Department of Health, instead of by ”the Criteria for the Management of the Hillsides Development” required by the Ministry of Interior. In view of the above guide, the collection of geological data does not seem to be enough for the practical design. Thus, many environmental and geological problems, such as groundwater pollution and landslides, have occurred. This article aims at studying topography, geology, site selection criteria for waste landfills, suitable types of slope protection, and design for pollution barrier. The data on the site of landfills related to geological investigation are synthesized. Several specific recommendations of groundwater pollution barrier design are also introduced.