Use of Tension Infiltrometer Data with Unsaturated Hydraulic Conductivity Models

Abstract

AbstractA new method is presented to estimate the relationship between unsaturated hydraulic conductivity and soil‐water pressure using tension infiltrometer data. In this method, both the early transient and the subsequent quasi‐steady stages of the infiltration process underneath a tension infiltrometer disc are analyzed. Our investigation indicates that the infiltration rate at early times closely follows the aquare‐root‐of‐time relationship (Philip, 1969). This behavior permits the evaluation of the sorptivity, which is an integrated measure of soil diffusivity. At later times, three‐dimensional quasi‐steady flow beneath the infiltrometer disc develops, and the Wooding equation for flow from a circular pond is used to evaluate the sorptive number and the saturated hydraulic conductivity. Simple algebraic expressions are introduced to relate the sorptivity and sorptive number to the parameters of the Brooks and Corey model of unsaturated hydraulic conductivity. The method described here extends the utility of tension infiltrometer data to a large class of hydraulic conductivity models and provides an in situ technique to determine suitable parameters values for these models.An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.