Fecal coliform level at point A on a river flowing at $90$ MGD with a velocity of $10$ mpd is $100/100$ ml$.$A discharge of $10$ MGD is applied at point A$,$ with a fecal coliform level of $5$x$106/100$ ml$.$ Water sample from the river at a point B$,5$ miles downstream of A has fecal coliform concentration of $185,000/100$ ml$.$

$1.$ Determine the in$-$stream decay coefficient for fecal coliform $[1/$day$]$

$2.$ If new regulations require coliform reduction by a factor of $1,000$ at B$,$ by what $\%$ should the fecal coliform levels be reduced at point A prior to discharge into the river