Plateau Creek carries 5.0 m^3 /s of water with a selenium (Se) concentration of 0.0015 mg/L. A farmer withdraws water at a certain flowrate (m3 /s) from the creek for irrigation. After using the water, half of the water withdrawn returns to the creek and contains 1.00 mg/L of Se. Fish in the creek are sensitive to Se levels over 0.04 mg/L. Required:
How much water (m3 /s) can the farmer withdraw from the stream to maintain Se at 0.04 mg/L after the contaminated water is returned to the creek?