They can drill all year round, the biggest constriction is break-up and freeze up when planes cant land on the lake. With fuel being limited to all because of no freight coming in on ice ,it will be dicey if a lot of drilling could get done until after break up. Those big drills I have been told won't fit in an Otter very well so they may have to wait till airstrip is finished to utilize larger aircraft, or they will have to be helicoptered in with a big lift machine