Combine water, salt, sugar, dill, and soy sauce in a large bowl, stirring until salt and sugar dissolve. Pour salt mixture into a large zip-top plastic bag. Add ice and salmon; seal. Refrigerate 2 hours, turning bag occasionally.
Soak the wood chips in water for 1 hour. Drain well.
Prepare the grill for indirect grilling, heating one side to medium and leaving one side with no heat.
Place half of wood chips on hot coals. Remove salmon from bag; discard brine. Pat salmon dry with paper towels. Place salmon on grill rack coated with cooking spray over unheated side. Close lid; grill 10 minutes. Place remaining wood chips on hot coals; close lid, and grill 15 minutes or until fish flakes easily when tested with a fork. Sprinkle with black pepper and garnish with dill sprigs, if desired.