Question $2.$ The suspended solids in runoff into a detention pond are dominated by three primary particles, with characteristics given below. Determine the fraction of each particle removed and the fraction of total suspended solids removal through the pond assuming ideal sedimentation. The average pond area is $1\mathrm{.}0$ acres with a steady state flow rate of $120$ ft$3/$s$.$

Sediment

Size $($mm$)$

Specific Gravity

Concentration $($mg$/$L$)$

Sand

$0\mathrm{.}13$

$2\mathrm{.}65$

$80$

Silt

$0\mathrm{.}02$

$2\mathrm{.}8$

$10$

Brake Dust

$0\mathrm{.}05$

$5\mathrm{.}4$

$2$

Hint: Ri $=$ vi$/($Q$/$A$),$ fraction of smaller particles with velocity vi removed.