The BOD in a stream is $2\mathrm{.}5$ mg$/$L and the DO is $7\mathrm{.}6$ mg$/$L$.$ Stream flow is $10$ x $10\backslash$deg L$/$d$.$ A treated sewage effluent with BOD $76$ mg$/$L is discharged into the stream at a rate of $4$ x $106$ L$/$d$.$ The DO of the sewage effluent is $1\mathrm{.}5$ mg$/$L$.$ Assume the deoxygenation and reaeration constants are $0\mathrm{.}2$ d$-$l and $0\mathrm{.}5$ d$-\text{'}$ respectively and the saturated DO level is $9$ mg$/$L$,$ determine the minimum DO level in the stream. If stream velocity is $0\mathrm{.}015$ m$/$s$,$ where does the minimum DO occur?