Level 1 trench essentially means maximum one trench counter. Most spaces allow two levels of trenches (two trench counters), but square and mountain spaces may only have one trench.
Ah OK, I've got it now. Last part of 18.104.22.168 "...up to a maximum of two." and 22.214.171.124 "Standard area 2, Square or Mountain area 1, Circle area None". The word Level threw me. Thanks Kirk!