No, it couldn't. It would basically be a few Chernobyls in the worst case (a 1 in 1000 year asteroid impact winning the 1 in 100 million lottery and hitting th

No, it couldn't. It would basically be a few Chernobyls in the worst case (a 1 in 1000 year asteroid impact winning the 1 in 100 million lottery and hitting the dump) and that mostly means extra birth defects and cancer (you wouldn't want to live somewhere that gave you a 10% chance if dying due to cancer age 40, but you could still have a civilization in such a location). It doesn't end life in the impacted area. For intentional attacks there are much much easier ways of killing a lot of people.