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The removal efficiency of phosphorus during storm events can be assumed to be primarily associated with the removal of TSS. Urban water quality data have indicated that a high proportion of TP in urban stormwater is in particulate form. For this study, phosphorus is assumed to be distributed over the particle size range in proportion to the surface area of particles of each size range. Combined with the adopted TSS particle size distribution in Figure 1, and smoothed slightly, this produces the TP curve also shown on Figure 1. There has been little emphasis placed on the distribution of particles less than about 2 mmmicrons, because under the sedimentation approach adopted, they are never likely to settle anyway.
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