$(50)1.$ A study has shown that under low flow conditions, the flow in a given stream

located at an elevation of $600$ feet above $msl$ will be $20cfs$ just above a STP

outfall. The STP discharge will be $3\mathrm{.}23$ MGD $(5cfs.$ A laboratory study on a $4$

parts stream water and $1$ part effluent mixture sample yielded the following

results Carbonaceous BOD; NBOD $=$ Nitrogeneous BOD; TBOD $=$

CBOD $+$ NBOD$)$:

Ultimate CBOD$=10\mathrm{.}0m\frac{g}{L}$

$k_d(20C)=\frac{0\mathrm{.}30}{?}$ day

Ultimate NBOD $=20\mathrm{.}0m\frac{g}{L}$

$k_n(20C)=0\mathrm{.}0$ for first $3$ days in bottle or stream and $\frac{0\mathrm{.}18}{?}$ day after $3$ days

NBO$\frac{D}{N}{H}_3-N=4\mathrm{.}5$

At a stream temperature of $25C,$ determine the following for $k_d,=1\mathrm{.}08$

for $k_n,$ and $=1\mathrm{.}02$ for $k_a)$:

a$.$ The $5-$day $20C$ CBOD, and the $N{H}_3-N$ concentration of a sample collected

immediately below the outfall.

b$.$ The ultimate CBOD, the ultimate NBOD, the $5-$day $20C$ CBOD, the $5-$day

$20C$ TBOD, and the $N{H}_3-N$ concentration of a sample collected at a point

$6$ days travel time downstream from the outfall.

c$.$ The mean velocity in the stream segment downstream from the outfall

which has the following properties: slope $=8f\frac{t}{m}$i and upstream

drainage basin area $=200$sqmi. Under these conditions the stream

velocity may be estimated from the following expression:

$U=0\mathrm{.}40+4\mathrm{.}1qS{S}^{0\mathrm{.}5},q$: instream discharge $=\frac{Q}{?}$ drainage basin area

in mi$/$day$,S$ in $f\frac{t}{m}i,Q$ in cfs$,A$ in sq $mi).$

d$.$ The atmospheric reaeration coefficient $(25$C$)$ for the segment by the

Dobins$-$ O'Connor model. Assume D is constant for the latter. The

mean depth is $2ft.$ Use the velocity determined in part $c.$

e$.$ The percentage of D$.$O$.$ saturation when the stream D$.$O$.$ is $5m\frac{g}{L}$ in the

summer $(25C)$ and winter $(4C).$ The chloride effect may be neglected.