An unseeded BOD test is conducted on a polluted surface water sample by adding 100 mL of the sample to a 300-mL BOD bottle and filling with dilution water. The initial dissolved oxygen (DO) concentration was 8.2 mg/L and the final DO concentration after five days of incubation at 20 degrees Celcius was 2.9 mg/L. Calculate the BOD5 of the original sample.