PREDICTING FIELD-SCALE SOLUTE TRANSPORT USING IN-SITU MEASUREMENTS OFSOIL HYDRAULIC-PROPERTIES

Predicting unsaturated solute transport using measured hydraulic param eters has been difficult due to the inherent variability of soil prope rties, and the difficulty in obtaining accurate estimates of hydraulic properties in situ. The objective of this study was to determine if i n situ measurement of soil hydraulic conductivity, the alpha soil para meter, and the water content (theta) vs. pressure head (h) relationshi p could be used to predict field-scale solute transport. A series of s teady-state solute transport experiments were conducted on a Fox sand (fine-loamy over sandy or sandy-skeletal, mixed, mesic Typic Hapludalf ) soil in Ontario, Canada. The transport of Cl- under steady-state wat er Bur was monitored in three separate experiments using solution samp lers. Steady-state water flux densities applied at the soil surface we re 9.72 x 10(-6), 1.53 x 10(-5), and 8.68 x 10(-8) m s(-1), respective ly, for the three sites. After completion of the transport experiments at Site II, measurements of soil hydraulic conductivity and the alpha parameter were made using the Guelph pressure infiltrometer (GPI) bes ide each location and depth where solute breakthrough curves (BTCs) we re measured, as well as at the soil surface. Undisturbed soil cores we re taken at each location where GPI measurements were made for estimat ing the parameters in the theta(h) using van Genuchten's equations. Th e GPI- and core-measured hydraulic parameters obtained at Site II were used to predict the field-scale solute travel time probability densit y function (PDF) at the same site, and at Sites I and III using a stoc hastic-convective model. Observed solute travel time PDFs were predict ed quite wed at high surface water fluxes, which were close to the fie ld saturated hydraulic conductivity, K-fs by both the GPI and core met hods. Both methods underpredicted the variability of the observed trav el time PDF.