Plateau creek carries 5 m3 /s of water with a selenium concentration of 0.0015 mg/l. a farmer starts withdrawing 1 m3 /s of the creek water to irrigate the land. during irrigation, the water picks up selenium 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 run off to the creek contains 1 mg/l of selenium. selenium can be treated as a conservative substance for the purposes of this problem. also assume that the stream does not pick up more selenium from any other source. a. if the farmer irrigates continuously, what will be the steady‐state concentration of selenium in the stream downstream from the farm (after the irrigation run‐off returns to the stream)? express your answer in mg/l, g/l, ppm, and ppb. b. fish are sensitive to selenium levels over 0.04 mg/l. the farmer agrees not to use more water than will keep the stream selenium levels below this critical concentration. how much water can the farmer withdraw from the stream to use for irrigation?