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<br />TABLE 11 <br /> <br />. <br /> <br />Average Concentrations of Various Pollutants for <br />Various Time Intervals of Runoff, Cincinnati, Ohio <br />(Weibel, Anderson and Woodward, 1964) <br /> <br />Parameter 0-15 Min. 15-30 Min. 30-60 Min. 60-120 Min. 120+ <br />COD, mg/~ 170 130 110 97 72 <br />BOD, mg/~ 28 26 23 20 12 <br />SS, mg/~ 390 280 190 200 160 <br />VSS, mg/~ 98 69 47 58 33 <br />Total N, 3.6 3.4 3.1 2.7 2.3 <br />mg/~ <br />P04' mg/~ 0.99 0.86 0.92 0.63 0.63 <br /> <br />McElroy and Bell (1974) reported that a "first-flush" of <br /> <br />suspended solids and BOD was exhibited at the urban sampling <br /> <br />station; however, no first flush of BOD was apparent at the semi- <br /> <br />urban/rural station, and only a very small first flush of <br /> <br />suspended solids was observed. It was also reported that <br /> <br />although first flushing was evident, several subsequent flushes <br /> <br />of suspended solids also occurred after the initial flush when <br /> <br />the flow increased dramatically. However, upon reaching maximum <br /> <br />flow, solids concentrations decreased and remained constant <br /> <br />regardless of the flow pattern. This implies that a minimum <br /> <br />flow is required to completely flush the solids from the basin. <br /> <br />De Fillipi and Shih (1971) studied the time and flow <br /> <br />. <br /> <br />dependency of storm sewer flows in Washington, D.C. They also <br /> <br />found the "first-flush" to be evident in most cases. Storms with <br /> <br />various durations and intensities, as well as consecutive storms, <br /> <br />25 <br /> <br />... <br />