It is possible that a drainfield was run off of the dry well in an attempt to save money. If the drainfield does run off of the dry well, then the drywell is operating as a type of holding sytem for the water before it reaches the drainfield. If the pipes are not clogged and the drainfield is operating properly, then I would probably suggest that you leave the drywell alone. It is not responsible for absorbing water and other than perhaps creating a problem in the future, it is not affecting the operation of the drainfield. If you wanted to do anything to it, then think about filling it in and piping the drainfield directy to the septic tank outlet. If you do this, consider putting a cleanout between the tank and the drainfield to allow you to moniter the water levels and treatment the drainfield in the future.