A literature search was conducted in the area of mass dispersion from instantaneous and continuous sources in bounded and unbounded flows. This study presents a mathematical model consisting of only two nondimensionalized variables and capable of generating universal concentration profiles of the pollutants in a rectangular channel flow for specified initial and boundary conditions. Determination of diffusion coefficients, mixing distance, sampling location and number of sampling points in a cross-section is possible. In other aspects, determination of the minimum sampling frequency required to collect a representative composite sample based on the previous effort is reexamined. It is concluded that a minimum sampling frequency of eight (8) for most of the flow and concentration patterns in the complete mixing zone is sufficient to provide enough accuracy for a representative sample collected by three out of four known compositing techniques.