Plateau Creek carries 5 m/s of water with Se concentration of 0.0015 mg/L. A farmer starts withdrawing 1 m/s of the creek water to irrigate his land. During irrigation, the water picks up Se from the salts in the soil. One-half of the irrigation water is lost to the ground and plants, and the other half is returned to Plateau Creek. The irrigation runoff to the creek contains 1 mg/L Se. Se is a conservative, nonreactive substance, and stream does not pick up Se from any other source (a) If the farmer irrigates continuously, what will be the steady-state concentration in the stream downstream from the farm (after irrigation runoff returns)? (b) Fish are sensitive to Se levels over 0.04 mg/L. The farmer agrees not to use more water than will keep the stream Se level below 0.04 mg/L. How much water can the farmer withdraw?