What method of sanitary landfill involves placing waste in layers from a significant depth?

The valley or ravine method is a landfill technique that involves placing waste into natural depressions or ravines, utilizing the existing topography to manage waste effectively. This method is advantageous because it takes advantage of the landscape to reduce the amount of earth-moving necessary when establishing a landfill site. By placing waste in layers within these natural features, the approach promotes better containment and can facilitate the leachate management process as well, making it a more environmentally sensitive method compared to others. This method typically requires consideration of hydrological factors to prevent groundwater contamination and to manage landfill gas emissions as the waste decomposes.

In contrast, the area or ramp method generally involves creating a gradual ramp for depositing waste, which may not utilize depth as effectively as the valley method. The trench method focuses on digging trenches to dispose of waste, which does not utilize natural features and may not optimize the use of vertical space. The open dump method is the least controlled and lacks the sanitary aspects required for modern waste disposal practices, as it involves simply dumping waste without consideration for environmental impact.