Measuring Air Conductivity for Synthetic Soils. The objective of measuring air conductivity for synthetic soils was to develop regression equations to estimate saturated hydraulic conductivity, Ks, from grain-size analyses. The measured air conductivity values were converted to saturated water conductivity, and a regression equation was derived to estimate saturated hydraulic conductivity using selected grain-size parameters of the synthetic soil samples. The expectation was to use the regression equation to estimate Ks for field soil samples. Four different soil textures were selected to encompass a wide range of saturated hydraulic conductivity values. The soil textures included #16 silica sand, #50 silica sand, #125 silica sand, and rock flour (pulverized sand that has the consistency of flour). Mixing different portions of these four soil types created a series of soil textures. The air permeameter was then used to estimate hydraulic conductivity for each different soil sample using a Cf of 15. This is the appropriate correction factor if the air conductivity is measured at laboratory temperatures, and if the hydraulic conductivity is also for laboratory temperatures, with assumed laboratory temperature of 20° C. The mixtures used to develop the different soil samples, the measured Kair values, and the estimated saturated hydraulic conductivity are given in Appendix A. These hydraulic conductivity values were used to develop regression equations relating soil texture information and hydraulic conductivity. Limitations and errors associated with this approach are discussed below in Sections 2.5 and 2.6. Equation 2.6 was used to calculate Kair. H0 was measured from a ruler that was taped to the lower cylinder. When the seal was released from the upper cylinder, a stopwatch was used to record the time for the water to rise inside the lower cylinder. H1 was measured when the timer was stopped. The length of the soil sample was recorded with a ruler. The porosity, n, for each sample was estimated by measuring the volumes of solids and the bulk sample. Xxxxxxxx was then calculated with the following expression: n = Vpores = Vsample − Vsolids = 1 − Vsolids
