Currently, if you gather resources enough times on one spot of junk heap, it turns into dirt, from which no resources can be gathered. Since actual landfills and dumps don't consist of a light dusting of trash on top of a pile of dirt, I would suggest changing this mechanic so that instead of having a "clear terrain" effect, it has a "lower terrain" effect, digging a hole deeper into the junk pile. The junk shouldn't turn into dirt until the pile is excavated down to ground level.