Using time domain reflectometry, we carried out dielectric relaxation measurements on 1-propanol-water mixtures for the entire concentration range in the frequency range 100 MHz-25 GHz at 20, 25, and 30 degreesC. We have calculated the excess partial molar activation free energy, enthalpy, and entropy for 1-propanol, DeltaG(1PA)(E) DeltaH(1PA)(E), and Delta (S)(1PA), and those for water, DeltaG(W)(E), DeltaH(W)(E), and DeltaS(W)(E) from the relaxation times. In the region of X (molar fraction of 1-propanol) greater than or equal to0.14, DeltaH(1PA)(E) and DeltaS(1PA)(E) take nearly zero. This means that I propanol molecules in the mixtures find themselves in not a very different environment from that in pure liquid. In the water-rich region, DeltaH(1PA)(E) and DeltaS(1PA)(E), exhibit two maxima at X similar to 0.03 and X similar to 0.06, corresponding roughly to 0.9 and 0.78 g/cm(3) of water content, respectively. This fact, together with the results of the molecular dynamics studies of Sciortino et al. suggest the formation of two kinds of saturated hydration structures: the clathrate hydration shells with tetrahedral local arrangements of water molecules around X similar to 0.03 and nonclathrate shells with large cavities with three-coordinated local arrangements around X similar to 0.06. Hydrophobic hydration seems to partly share the same mechanism with structural enhancement in pure water by lowering local density.