JKB, quite simple actually. Imagine the soil strata (soil layers) have various soil type as water go from top to bottom as it percolates from an above ground water source, say a lake, pond, forest ground, or even from rain. As the water moves from the upper layers to the storage area below, like an underground reservoir or aquifer, impurities within the water get pulled from the water molecules, creating a higher ionic charge within the water structure, as the water percolates deeper and deeper into the ground. Pure water, or water molecular structure, is not H20. Rather, it's H2O2. There are still active sites for the oxygen to grab onto other molecules that around the soil. In the deep soil, what molecules are available, beside carbon, silica, oxygen (exist between gaps of soil structures), nitrogen, stabilized metals, and various other inert compounds under extreme pressure? The only thing that being exchanged under high pressure, possibly high heat would be hydrogen and oxygen.
Constant battle to occupy the missing bonds between oxygen, hydrogen, and various other molecules, oxygen is one of the stubborn molecule that will not give itself up. It rather bind to other oxygen, nitrogen, or carbon molecules to find a way to stabilize itself out rather than giving itself up. It will attempt to rip the hydrogen from other compounds aggressive if needed. So, in an underground reservoir, without pollutants within the strata, what can water adhere to but more oxygen and hydrogen molecules? Ground water is loaded with dissolved oxygen.
Just take this scenario. How can underwater creature found in caverns deep in the earth survive with lack of oxygen if the water source don't contain enough dissolved oxygen to survive on? How can cave explorer manage to go so deep into caverns without having continually air supplies given to them? Oxygen get continually renewed as water pull oxygen content from the upper strata to the lower bedrocks and reservoirs.
Hope I don't overstep my explanation somehow..geotechs and geologists? Mind adding more?
