Lots of rural properties have trash dumps; especially in OK. In most cases its not a big deal. Some states may order the land owner to clean up the dump but i never heard of this happening here in OK. i doubt the bank would turn down a loan unless the dump was a real monster.
I would not recommend that a landowner clean up a trash dump unless he is relatively certain there are no hazardous materials present. If you go prowling around in a dump and discover a really hazardous substance like PCBs, trichloroethylene, or Temik and report it; guess who pays for the cleanup? Hazardous waste cleanup is expensive to the extreme.