A wastewater plant discharges 3 MGD of effluent with a dissolved oxygen concentration of 0.5 mg/L into a chloride-free river flowing at 50 cfs. Upstream of the wastewater treatment plant outfall, the river is saturated with oxygen an at a temperature of 46.4 Fahrenheit degrees (8 Celsius degrees). What is most nearly the dissolved oxygen deficit (in mg/L) in the river just downstream of the outfall caused by the wastewater treatment plant discharge?