[en] Extrapolation of Darcy's law to the transport of water an solutes in unfractured poorly permeable rocks being studied for nuclear waste disposal is questioned. The hydrologic literature includes numerous references to both non-Darcian flow in dense materials devoid of macrofractures and microfractures and to threshold gradients below which no flow occurs. For such situations to occur, the pore-size range must be small enough so that all pore water is sufficiently close to mineral surfaces to be affected by the surficial forces. Then the flow will be non-Newtonian and non-Darcian, and solute transport will be by molecular diffusion. If fluid transport in very dense unfractured rocks is non-Darcian, useful methods of testing candidate host rocks become apparent. In situ nondestructive pressure testing of canister waste emplacement boreholes in a mined repository can verify the absence of both fracture flow and Darcian flow. 18 references