As you may already know, a chemical reaction refers to the "mixing" of some chemical compounds called reagents, which will have the atoms rearranged among themselves, transforming them into other chemical compounds. This rearrangement of atoms is done with energy expenditure that can be perceived by the reactions that happen with temperature changes, light release, among others.
In summary, a chemical reaction occurs when energy is released, at which time the energy levels between reagents and products follow the following order:
The word sponge is more appropriate to use than Underground river since an underground river can loose water while an aquifer cannot loose water, unless it is open-air and above ground. then the aquifer would slowly loose water due to evaporation from the sun.