7. A treatment plant has a peak Q 5000 L/min, a chlorine contactor volume of 100 m that is at least filled at 80% of its full volume. The reservoir is baffled and has a BF of 0.7. if the plant needs to achieve 1 log removal of Giardia to meet its disinfection requirement, and that the pH if 7.0 and the water temperature is 15C, what is the level of exiting free chlorine that should be maintained for disinfection?