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<br />It can be noted that after one or two days after street sweeping <br /> <br /> <br />or a storm, the accumulated solids become nearly constant on <br /> <br /> <br />street surfaces in residential or commercial areas. Apparently <br /> <br /> <br />wind and auto movement resuspend deposited material after it <br /> <br /> <br />reaches a certain depth and a constant level of accumulated <br /> <br /> <br />solids results. <br /> <br /> <br />The configuration of the sewer system has been considered <br /> <br /> <br />in a few studies. Contaminants may be introduced into storm <br /> <br /> <br />s,ewers through openings in the system. When violations of local <br /> <br /> <br />ordinances occur, additional contaminants find their way into <br /> <br /> <br />the system. Various wastes that are difficult to dispose of, such <br /> <br /> <br />as motor oil, transmission fluid, etc., often enter storm sewers <br /> <br /> <br />via street inlets. In separate storm sewers, these wastes will <br /> <br /> <br />be discharged untreated, or will collect until the next storm <br /> <br /> <br />washes them out (Lager and Smith, 1974). <br /> <br /> <br />Catch basins, which were originally installed to prevent <br /> <br /> <br />sewer clogging and to provide water seals to entrap odors from <br /> <br /> <br />sewers, have been found to be a significant source of pollutants <br /> <br /> <br />(APWA, 1969). A study in Chicago indicated that the liquid <br /> <br /> <br />remaining in the catch basin between runoff events tended to <br /> <br /> <br />become septic, and that the solids trapped in the basin took on <br /> <br /> <br />characteristics of anaerobic sludge. The BOD content of catch <br /> <br /> <br />basin liquid was found to be 60 ppm (50 to 85 ppm range) in a <br /> <br /> <br />residential area. It was also found that even for minor storms, <br /> <br /> <br />the BOD of the liquid was 7~ times that of the runoff which had <br /> <br /> <br />been in contact with street surface contaminants. Since the <br /> <br />. <br /> <br />30 <br /> <br />. <br />