06 Ea,v8= 04 02 12 16 18 Filtrate VoFume-gpm-hr FIGURE 8. 16 Effluent iron content and filtrate volume. Observations for curves were made after initial improvement period Numbers by curves indicate filtration rate Curve along"X"marks indi- cates constant pressure Rate of this run started at 6 gpm/ft- and decreased to 4 gpm/ft- as head loss increased. (Source: J. L. Cleasby and E. R. Baumann, " Selection of Sand Filtration Rates, "Jour AwWA,545),May1962:579.)