The Blue Ox Tannery has asked you to assist them in preparations to file for a NPDES permit to discharge wastewater into the Zmellsbad River. The DNR water quality criterion for the Zmellsbad River is 5.00 mg/L of DO. They have asked you the following questions: What is the critical DO and where (at what distance) downstream does it occur? They have provided you with the following data. They pertain to the 7-year, 10-day low flow at the tannery.

Parameter Blue Ox wastewater Zmellsbad River
Flow, m3/s 1.148 7.222
GODS at 15°C, mg/L 90.00 N/A
ROD. at 15°C. mg/L N/A 7.66
DO. mg/L 1.00 6.00
Temperature. °C 15.0 15.0
k at 20°C. d-I 0.3685 NA
Speed. m/s N/A 0.300
Depth. m N/A 2.92
Bed-activity coefficient N/A 0.100