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Permit No. NCG020000 <br /> 25. Total Flow <br /> The flow corresponding to the time period over which the sample collection occurs. The <br /> total flow calculated based on the size of the area draining to the outfall, the amount of <br /> the built-upon surfaces within the drainage area, and the total amount of rainfall <br /> occurring during the sampling period. <br /> 26. Toxic Pollutant <br /> Any pollutant listed as toxic under Section 307(a)(I) of the Clean Water Act. <br /> 27. Types of Samples. <br /> a. Grab samples are individual samples collected instantaneously. <br /> b. Composite Sample: a composite sample shall mean: <br /> (1) A flow-weighted composite sample, which is a mixture of aliquots collected at a constant <br /> time interval, where the volume of each aliquot is proportional to the flow rate of the <br /> discharge at the time the sample is collected; or <br /> (2) A time-weighted composite sample, which is a mixture of equal volume aliquots collected <br /> at a constant interval of time. <br /> A composite sample can be obtained from the collection of a series of grab samples, taken <br /> at intervals of no greater than 20 minutes. The grab sample to be composited must be of <br /> no less than 100 milliliters. <br /> 28. Visible Sedimentation <br /> Solid particulate matter, both mineral and organic, that has been or is being transported <br /> by water, air, gravity, or ice from its site of origin which can be seen with the unaided <br /> eye. <br /> 29. Waste Pile, <br /> Any noncontainerized accumulation of solid, nonflowing waste that is used for treatment <br /> or storage. <br /> 30. 25-year. 24 hour storm event <br /> The maximum 24-hour precipitation event expected to be equalled or exceeded, on the <br /> average, once in 25 years. <br /> • <br /> Page 12 of 24 Pages <br />