[1] Many details about the flow of water in soils in a hillslope are unknowable given current technologies. One way of learning about the bulk effects of water velocity distributions on hillslopes is through the use of tracers. However, this paper will demonstrate that the interpretation of tracer information needs to become more sophisticated. The paper reviews, and complements with mathematical arguments and specific examples, theory and practice of the distribution(s) of the times water particles injected through rainfall spend traveling through a catchment up to a control section (i.e., "catchment" travel times). The relevance of the work is perceived to lie in the importance of the characterization of travel time distributions as fundamental descriptors of catchment water storage, flow pathway heterogeneity, sources of water in a catchment, and the chemistry of water flows through the control section. The paper aims to correct some common misconceptions used in analyses of travel time distributions. In particular, it stresses the conceptual and practical differences between the travel time distribution conditional on a given injection time (needed for rainfall-runoff transformations) and that conditional on a given sampling time at the outlet (as provided by isotopic dating techniques or tracer measurements), jointly with the differences of both with the residence time distributions of water particles in storage within the catchment at any time. These differences are defined precisely here, either through the results of different models or theoretically by using an extension of a classic theorem of dynamic controls. Specifically, we address different model results to highlight the features of travel times seen from different assumptions, in this case, exact solutions to a lumped model and numerical solutions of the 3-D flow and transport equations in variably saturated, physically heterogeneous catchment domains. Our results stress the individual characters of the relevant distributions and their general nonstationarity yielding their legitimate interchange only in very particular conditions rarely achieved in the field. We also briefly discuss the impact of oversimple assumptions commonly used in analyses of tracer data.

Parameter estimation procedures involving solution of the inverse flow problem pertinent to a transient experiment constitute a powerful method of determining the soil hydraulic properties. One of the problems associated with these procedures is the selection of an appropriate model to describe the soil hydraulic properties. Three different models were considered: those of van Genuchten (VG) and Brooks and Corey (BC) model, and the exponential model of Gardner for the hydraulic‐conductivity‐soil‐water‐pressure relationships, coupled with a new expression for the soil‐water‐content‐soil‐water‐pressure relationship (GR model). For a given model the soil hydraulic properties were determined from simulated and measured outflow experiments supplemented with water content at a soil water pressure head of −15,000 cm H2O, using the parameter estimation procedure of Kool et al. (1985a) and data from two soils: a hypothetical sandy loam soil (assumed to be described by the VG model) and a silt loam soil. Model validation tests were performed, and the most appropriate model was selected from the candidate models by discrimination tests using the Akaike Information Criterion (AIC). In the case of the hypothetical sandy loam, the VG model was found to be the most accurate and most consistent with the data. The performance of both the BC and the GR models (in terms of the AIC) was less good but very similar to each other. In the case of the silt loam soil, the VG model with additional parameter m, which accounts for the correlation between pores and for the flow path tortuosity (m=2.02) rather than a constant m=0.5, was found to be most accurate and most consistent with the data. The performance of the BC and the GR models was similar when m was considered as an unknown parameter instead of a constant.

Core scale estimates of soil parameters of the Gardner‐Russo and van Gemachten models of the hydraulic conductivity and water retention functions were obtained for 417 undisturbed soil cores taken from a wall of a trench (20 m long, 2.5 m deep), using a procedure based on inverse problem methodology. These estimates were used to evaluate the first two statistical moments of the underlying random space functions (RSFs), using the restricted maximum likelihood estimation procedure, coupled with the weighted least squares procedure, to estimate parameters of models of the covariance and the drift functions of the pertinent RSFs. The fitted models were used to evaluate the mean and covariance functions of the hydraulic conductivity and water rentention functions for given water saturations. Covariance functions of log‐saturated conductivity (log Ks) and the “shape” parameters of the Gardner‐Russo and van Genuchten models exhibited statistical anisotropy characterized by aspect ratios that vary between 3 to 4. Correlation scales of log Ks were larger than those of the “shape” parameters. Consequently, the product of the variance of log unsaturated conductivity and its correlation scale remained essentially invariant for a considerable range of water saturation. The implications of these results regarding stochastic modeling of transport in heterogeneous porous formations and possible applications of the results of this study are discussed briefly.

This study examined subjective patient experiences of the psychosocial consequences of multiple sclerosis (MS). Fifty patients were interviewed regarding the effects MS had on their lives and interpersonal relationships. These statements were collated and administered with a 5-point Likert scale to 94 MS patients. The responses were subjected to factor analysis. Three areas of subjective patient experience of the psychosocial consequences of MS emerged: demoralization, benefit-finding, and deteriorated relationships. Of particular interest was benefit-finding, which included a deepening of relationships, enhanced appreciation of life, and an increase in spiritual interests. Although benefit-finding was related to adaptive coping strategies such as positive reappraisal and seeking social support, it was unrelated to depression and was related to higher levels of anxiety and anger. These findings indicate that benefit-finding is a substantial and poorly understood part of the illness experience for MS patients.

Although volatile organic compounds located in buried waste repositories or distributed through the unsaturated soil zone have the potential to migrate to the atmosphere by vapor diffusion, little attention has been paid in the past to estimating the importance of volatilization losses. In this paper a screening model is introduced which evaluates the relative volatilization losses of a number of organic compounds under standard soil conditions. The model is an analytic solution to the problem wherein the organic chemical is located at time zero at uniform concentration in a finite layer of soil covered by a layer of soil devoid of chemical. The compound is assumed to move by vapor or liquid diffusion and by mass flow under the influence of steady upward or zero water flow while undergoing first-order degradation and linear equilibrium adsorption. Loss to the atmosphere is governed by vapor diffusion through a stagnant air boundary layer. Calculations are performed on 35 organic compounds in two model soils with properties characteristic of sandy and clayey soil. The model identifies those compounds with high potential for loss during 1 year after incorporation under 100 cm of soil cover and also is used to calculate the minimum soil cover thickness required to reduce volatilization losses to insignificant levels during the lifetime of the compound in the soil. From the latter calculation it was determined that certain compounds may volatilize from deep subsurface locations or even groundwater unless the soil surface is sealed to prevent gas migration.