Here is some hints for excavation plan. Firsts, some crash sites are located over Miasma. Miasma is like fungus in AC, it will take damage to the unit over it every turn. So those sites may be left for later, the AI will not dig them. Second, the water crash sites also seem a little interest to AIs. They should be watched when a city is build close to them. Always first check the map for resource pods, especially the north and south poles, and then go for the crash sites, beginning with the closest ones so the explorer is close to a city to refill the module for the next site.