A facultative oxidation pond is to be designed for a community of 5000 people. Summer wastewater flow is 2000 m³/d, and the BOD₅ is 180 g/m³. Winter flow and BOD₅ values are 6000 m³/d and 90 g/m³, respectively. Average pond temperatures are 20˚C in the summer and 10˚C in the winter. Assuming that a CFSTR model is appropriate and that oxygen transfer will not be a problem, determine the pond volume required to reduce the influent BOD₅ to 20 mg/L.