Because of the purity of its groundwater source, a water utility only has to disinfect the water before delivery. The utility uses ozone as its primary disinfectant and treats 20MGD of water. The ozone is bubbled into the water as it passes sequentially through the 3 chambers of a disinfectant contact tank. Each chamber of the tank is well mixed, holds 100,000 gallons of water, and receives the same ozone dose. EPA requires that the Giardia concentration be reduced to 1/1,000 of its initial concentration. The coefficient of specific lethality and coefficient of dilution for ozone inactivation of Giardia under these conditions are 1.8 L/mgmin and 1.0, respectively. What is the minimum ozone concentration (in mg/L ) that must be used to achieve the required removal of Giardia