PS 4 Examples Even Year

# PS 4 Examples Even Year - UNIVERSITY OF CALIFORNIA LOS...

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UNIVERSITY OF CALIFORNIA, LOS ANGELES Civil and Environmental Engineering Department CEE 153 Introduction to Environmental Engineering Science Example Problems for Problem Set # 4 _____________________________________________________________________________ 1. A river with a steady flow Q a = 1 m 3 /sec flows into a small harbor with a volume V = 10 7 m 3 and a bottom area A = 10 6 m 2 . The flow then passes out of the harbor to the ocean. The harbor may be considered to be well-mixed. a) Seepage from old septic tanks causes the bacterial concentration in the river (just before it enters the harbor) to be c a = 10 4 /100 mL (i.e. 10 4 bacteria per 100 mL sample). The bacteria die off according to a first-order reaction rate k r = 0.5/day. Does the water in the harbor meet the swimming standard which is that the well- mixed concentration of bacteria in the harbor be less than 200/100 mL? [170/100 mL meets the standard] b) A dredging operation in the river removes a total mass flow of solids m dredge = 10 6 kg/day from the river bottom. About 1% of the mass of dredged material is lost by leakage into the river and enters the harbor as suspended solids.

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