Reference the previous problems for additional information.

$4.$ During this time of year, the White River saturation DO is $9\mathrm{.}0m\frac{g}{L}$ with actual DO concentration at $6\mathrm{.}2m\frac{g}{L}.$ The river is moving on average $1\mathrm{.}2$mile$\frac{s}{h}$our. If the reaeration constant is $\frac{0\mathrm{.}06}{d}ay$ and the deoxygenation constant is $0\mathrm{.}045/$day$,$ evaluate when the critical time occurs $($ d $).$

$\{\begin{array}{c}\text{:}D{O}_{\text{s}\text{u}\text{t}}=9\mathrm{.}0m\frac{y}{L}\\ v=1\mathrm{.}2& \text{m}\text{i}\text{l}\text{e}\text{s}\frac{?}{?}\text{n}\text{o}\text{w}\text{s}& k_r=\frac{0\mathrm{.}06}{d}ay\end{array}$

$D_a=D{O}_{\text{s}\text{a}\text{t}}-D_{\text{a}\text{c}\text{t}}=9\mathrm{.}0-6\mathrm{.}2=2\mathrm{.}8m\frac{y}{c}$

$L_a=30m\frac{m}{L}$

tart $=\frac{1}{k_r-k_c}ln[\frac{k_r}{k_d}1-\frac{D_a(k_r-k_d)}{(k_d{L}_a)}]$

$L_0=BO{D}_n$ from previons problem. Your ANSWER: $13\mathrm{.}5m\frac{g}{L}$