3.5 lbs/hr polymer / 28 lbs polymer/ton dry solids, You are processing 0.125 tons of dry solids per hour.
0.125 dry tons/hr * 2000 lbs/ton / 0.015 / 8.34 lbs/gal. You are processing about 2000gph or 33gpm of 1.5% solids.
(3.5 lbs/hr polymer / (2000ppm polymer * 8.34 lbs/gal)) * 10^6. You need about 210gph or 3.5gpm of dilution water to makedown polymer to 0.2% or 2000ppm.
JL