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This study investigated how features of mass distribution within a source area control the pattern of contaminant plume evolution. A series of numerical trials was conducted which simulated contaminant migration in a three-dimensional saturated porous media with multiple source patches representing zones of contamination. Results showed that the extent of mixing near the source was greatly affected by both advection and dispersive mixing processes. The factors affecting the concentration distribution in the dissolved plume were size and distribution of source patches, dispersivity values, and the ratio of total patch area to the source area. The influence of dispersive mixing increased as the size of source patches decreased. However, dispersion was less important when patches were clustered or the ratio of total patch area to the source area increased. The variations in concentration values near the source, which were caused by differences in sizes and distribution of patches, diminished as the contaminant traveled further from the source. This result implies that detailed information on source characteristics generally would not be required beyond a certain travel distance. The exception in this regard is the ratio of total patch area to the source area, i.e., a zero-difference point. However, the location of this zero-difference point cannot be predicted easily because the location was affected by several source characteristics.