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14-4 <br />intended to retain soil and other materials on the site during <br />construction. This type of SB is later converted to some other use such <br />as open space or provides land for additional development. <br />In contrast, a SB may also be a permanent measure in an urban and <br />urbanizing area intended to prevent suspended solids, buoyant debris, <br />and adsorbed/absorbed pollutants from entering environmentally sensitive <br />areas such as lakes, rivers, and wetlands. A permanent SB could be <br />constructed, at least in rough form, prior to the initiation of land <br />development and initially serve the same purpose as a temporary SB. <br />~, a and 9ih-^,rface ns at la ions <br />Most SB are surface facilities, that is, they are constructed on the <br />land surface and are readily visible. Some SB are constructed below <br />ground, a common example being the sumps in stormwater system catch <br />basins. Although not common, large sub-surface SB have been designed <br />and constructed. For example, Skokie, Illinois, is constructing eight <br />large sub-surface stormwater detention facilities, each of which <br />includes a separate sedimentation section. <br />The possibility of permanent and temporary installations, single and <br />multi-purpose arrangements,_ rural and urban sites, and surface and sub- <br />surface construction suggest many possible SB configurations. While <br />