When the groundwater saturates the soil or sediment around it, organic matter can freely move between the phases. Groundwater has its own sources of natural organic matter including:
* organic matter deposits, such as kerogen and coal.
* soil and sediment organic matter.
* organic matter infiltrating into the subsurface from rivers, lakes, and marine systems."

Organisms decompose into organic matter, which is then transported and recycled. Not all biomass migrates,