The importance of particle characterization in stormwater runoff.

: Treatment units for stormwater management are being routinely required for new construction and upgrading of older facilities. This paper shows how particle size distribution affects the removal of sedimentation units and how erroneous results are often obtained if one uses simple overall removal efficiency or if the particle size distribution is not considered. Two full-scale devices are used for demonstration. A hydrodynamic device, which generally have low, overall suspended solids removal efficiency, is used for the first case, and it is shown that it actually removes large particles very well but has virtually no removal of small particles. The second case is for a dry detention basin. It is shown that the removal rates are generally in accord with sedimentation theory, removing larger and medium size particles well. Using particle size distribution in evaluating treatment unit performance is a more accurate and precise way of determining the actual performance.