Fig. 1. Schematic representations of four scenarios for dense nonaqueous phase liquid (DNAPL) source zones in sandy aquifers: (a) DNAPL penetrates to bottom of homogeneous sand aquifer to form a bottom pool, (b) DNAPL penetrates through homogeneous sand and accumulates in a layered transition zone, (c) DNAPL forms layers of residual and free-product DNAPL suspended in the sand aquifer, (d) DNAPL forms multiple layers distributed throughout the aquifer thickness. Note that all scenarios have residual trails because the source zones are represented at early time.