Mild spoilers today.
The hot springs location, like most things in SRPG, serves more than one purpose. The most immediate way in which it becomes relevant to the plot is the discarded refuse (see also: Litterbug Quest), but there’s more than meets the eye.
Ranger Bob suspects local ‘youths’ of scattering trash around, given their keen interest in the hot springs as a hangout spot. It will be up to the player to determine if this is the case, or formulate an alternate theory.
While we’re on the subject, why is there a hot springs here to begin with? The mountain is miles away, on the other side of town. Might be worth looking into.