A sanitary landfill is not about the contents of the landfill but more about how the waste is managed. A liner protects the groundwater and the soil from leaching substances until the components have degraded enough to be safe to the surrounding environment. The design and construction of a landfill is quite extensive and involves more than dumping trash in a hole in the ground. Preparation of the area is extensive to prevent short term damage ot the environment as well as long term damage due to the leachate. A sanitary landfill will have a pump system in place to remove the leachate so that is is not released into the surrounding soil or groundwater.
A sanitary wrapper on a sandwich protects the sandwich inside. The sanitary landfill liner protects the surroundings from the waste.