$4\mathrm{.}10$ In the winter, a stream flows at $10\frac{m^3}{s}$ and

receives discharge from a pipe that contains road run$-$

off. The pipe has a flow of $5\frac{m^3}{s}.$ The stream's chlo$-$

ride concentration just upstream of the pipe's

discharge is $12m\frac{g}{L},$ and the runoff pipe's discharge

has a chloride concentration of $40m\frac{g}{L}.$ Chloride is a

conservative substance. $($a$)$ Does wintertime salt usage

on the road elevate the downstream chloride concen$-$

tration above $20m\frac{g}{L}?($b$)$ What is the maximum

daily mass of chloride $($metric tons$/$day$)$ that can be

discharged through the road runoff pipe without

exceeding the water$-$quality standard?