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?

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).

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