An engineered burial of refuse. The refuse is dumped into trenches and compacted by bulldozer, where, it is hoped, @[email protected] @[email protected] by microorganisms decomposes the organic matter to @[email protected] compounds (H₂O, CO₂, etc.). Moisture is essential for the biological degradation and groundwater assists the process except when it fills air voids and prevents the transport of oxygen to the refuse. Land fills of unsatisfactory design can be major sources of air, water and soil pollution.