A river has a steady-state flow rate of 50 m3/s and a total dissolved salt concentration of 300 mg/L. An agricultural operation has applied for a permit to discharge an irrigation return flow of 5 m3/s to the river. You are an engineer for the State, and charged with determining the maximum allowable salt concentration in the discharge. A water-quality assessment for the entire river has indicated that salt concentrations should not exceed 500 mg/L in this stretch of the river in order to allow for use of the river as a drinking water source.
a. Draw a mass balance diagram to assist with analysis of this problem.
b. Develop a water balance to determine all relevant flow rates for the system.
c. Determine the allowable dissolved salt concentration in the irrigation return water.