We don't know but ArsonistHotdog has the most obvious answer, the weird part is that it's locked, and there's that much in there... but then again, there's also a literal bunker of unknown size right outside the station and huge dumpsters outside that were likely actually used at one point, although how cars and trucks got there with no road is an iffy question (with the new tree meshes that have been on the map for a while and a base re-design with a parking lot, there's probably a map overhaul imminent to match which will include a main road from the security gatehouse, if I were a betting man)