1. In a bowl combine buttermilk, sour cream, cucumbers, garlic, salt, pepper, dill and chives. Mix well. Cover and chill at least 4 hours.
2. Meanwhile, bring 4 cups water to a boil in a saucepan with thyme, bay leaf and parsley.Add the shrimp. As soon as the water returns to a boil, take the saucepan off the heat and let shrimp cool in the water. When cool, shell and devein shrimp; chop in small dices. Add shrimp to soup just before serving. Garnish with dill sprigs.