In winter, rain freezes to ice and expands, widening the cracks. And so on, year in, year out, century after century. The cracks not only let in water, they also provide pathways for plant roots and for burrowing animals. However, plants maintain their physical stability, and they gather water and nutrients, through roots, which can penetrate a landfill cap, destroying the cap's integrity. Burrowing animals of concern include woodchucks, badgers, muskrats, moles, ground squirchipmunks, gophers, prairie dogs and badgers.
Earthworms alone can have a devastating impact on a landfill cap.
Earthworms pass two to 15 tons of soil through their digestive tracts per acre per year. They give evidence that worm channels allowed plant roots to grow to a depth of nine feet in Nebraska clay soils. Unfortunately, that is one of the fundamental dilemmas left us by the normal processes of change in the natural world, be they the progressive conversion of a grassy field to a forest or the utilization of cracks in concrete sidewalks by ants and dandelions. This same successional development process, so intensively studied in the ecological literature, will detrimentally affect long-term landfill integrity. A perfectly silly idea.