There is actually spell called The Sudden Well in Against the Dark that creates a well-shaft. While quite suitable for dropping bad people 100+ feet into the earth, it's also useful in the capacity you describe - perhaps in combination with an InTe(Aq) spell of some kind to search for water beneath the earth, and some sort of ritual (Muto or Creo Terram?) if you'd like to make the well permanent and structurally stable.