From $1929$ to $1971,$ Monsanto manufactured PCBs and dumped their PCB containing waste into

the Choccolocco Creek in Anniston, AL$.$ The MCL for PCBs in drinking water is $5$x$10-4$ mg$/$L

and PCBs biodegrade with an associated pseudo$-$first$-$order biodegradation rate constant of $0\mathrm{.}44$

h$-1.$ Derive an expression for the steady$-$state concentration of PCBs in the creek given a creek

velocity of $1$ km$/$hr$.$