5) (20 points) An international organization has recently built a state-of-the-art hospital in Mirebalais, Haiti. The hospital includes on-site sewage treatment, which is then discharged into a nearby river and

is the only source of BOD in the river. Given the below information, calculate (a) the critical distance at which the minimum DO occurs(in miles), and (b) the minimum DO. The ultimate BOD just below the discharge = 30 mg/L Saturated DO = 10 mg/L DO just below the discharge = 6 mg/L Deoxygenation rate coefficient (ka) at the temperature below the discharge = 0.30/day Reaeration rate coefficient (k;) at the temperature below the discharge = 0.9/day River velocity = 48 miles/day