1. A stream flowing at 10.0 m3/sec has a tributary flowing into it at 5 m3/sec,

Question

1. A stream flowing at 10.0 m3/sec has a tributary flowing into it at 5 m3/sec, The ferric chloride concentration above the juncture is 10 mg/l and the tributary concentration is 12 mg/l, assume complete mixing of the ferric chloride: a. Find the downstream concentration of the ferric chloride. Show your calculations and schematic of the stream conditions and configuration. b. Does the concentration of ferric chloride calculated above pose any risk to the population downstream? If so, why? If not, why not?

Explanation / Answer

Mass of FeCl3 stream flowing at 10m3/sec ( its concentration is 10 mg/L)= 10m3/sec*1000L/m3*10mg/L =105 mg /sec

Mass of FeCl3 steam flowing at 5 m3/sec= 5*1000* 12 = 60000 mg/sec

Total mass = 105+6*104= 1,60,000 mg/sec

Flow rate ( assuming volumes are additive)= 10+5= 15 m3/sec=15*1000L/sec

Concentration of combined stream = 1,60,000/15*1000 mg/L=10.66 mg/L

This does not pose problem, since the tolerable concentration is much less. (200 mg/L)

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