In a former life, I used to have to convert sub-consultants' work into the office standard layering and text, before I could add my bit to it. As SDG says below, "purge" is invaluable. Sometimes, however, what you're trying to get rid of (spurious layers, fonts, etc.) is embedded in a symbol definition.

Just guessing: maybe in translation from 'terramodel' to ACAD, some entities were brought over as symbols with attributes [I found that to be quite common with the civil eng's site plans]. The most thorough cleanup might require finding them, exploding them back into basic geometry, and deleting any "hidden" and/or empty text field attributes... then purging a few more times.