A review of new TDR applications for measuring non-aqueous phase liquids (NAPLs) in soils

The time domain reflectometry (TDR) technique is a geophysical method that allows, in a time-varying electric field, the determination of dielectric permittivity and electrical conductivity of a wide class of porous materials. Measurements of the volumetric water content (θw) in soils is the most frequent application of TDR in Soil Science and Soil Hydrology. In last four decades several studies have sought to explore potential applications of TDR. Such studies (except those conducted on θw estimation) mainly focused on monitoring soil solute transport. In more recent times, innovative TDR approaches have also been implemented to extend current TDR fields of application to the problem of monitoring non-aqueous phase liquids (NAPLs) in variable saturated soils. NAPLs are organic compounds with low solubility in water and are characterised by a high mobility in the vadose zone. Due to their high toxicity, NAPLs constitute a severe geo-environmental problem, thus making detection and observation of such substances in soils an increasingly important issue. The present paper deals with these studies and aims to provide an up-to-date review of the main NAPL-TDR studies. To date, the literature has focused on TDR applications in three main fields: (i) NAPL monitoring in homogeneous, variable saturated soils, (ii) NAPL monitoring in layered variable saturated soils, and (iii) NAPL monitoring during soil decontamination processes. For an exhaustive and complete overview of TDR research in this field, we also recall the basic principles of TDR signal propagation, the functioning of a typical TDR device, and the dielectric mixing models that are widely used to interpret the dielectric response of NAPL-contaminated soils

LABORATORY-SCALE STUDY ON REACTIVE CONTAMINANT TRANSPORT IN SOIL BY MEANS OF ONE-DIMENSIONAL ADVECTIVE DISPERSIVE MODELS

We measured adsorption and transport of cadmium (Cd) in the presence of Ca2+ and Na+ salts of varying ionic strengths and pH by using batch and miscible displacement experiments, carried out on undisturbed and homogenized soil columns. A fluvent-vertic soil was used in this study. In the column experiment a clear effect of ionic strength on breakthrough curves (BTCs) of Cd2+ was observed when the Na+ concentration was increased from 0.02 to 0.2 M. The effect of increasing the Ca2+ concentration on Cd2+ absorption and transport was relatively less pronounced than that recorded for the Na+ solution. At low pH values, H+ ions competed strongly with Cd2+ ions and, at a high pH, precipitation was the main process taking place for Cd2+ sorption. The reliability of the advection- dispersion equation (ADE) was tested. When implemented within the least-squares method, the model produced a sufficiently precise space-time distribution of Cd2+ ion concentrations. The results of this study demonstrated also, that laboratory leaching experiments, when performed on homogenized soil columns, can greatly underestimate Cd2+ ions transport in the field and that preferential flow can increase the mobility and velocity of cadmium movement to the groundwater

Editorial of special issue “natural and artificial unsaturated soil slopes”

Natural and artificial slopes are frequently constituted, at least in part, by soils in unsaturated conditions [...

“The Dupes of Hope Forever:” The Loco-Foco or Equal Rights Movement, 1820s-1870s

This dissertation illustrates the impact of the Loco-Foco movement (1820s-1870s), most notably its role in the development of “Manifest Destiny,” the Free Soil Party, and the Republican Party. While historians have assumed that the Loco-Foco movement ended with the existence of the original third party in New York (1836-7), I pursue their philosophy and activism throughout the time and space of the late antebellum period. Loco-Focoism can be characterized as radical classical liberalism, including commitments to natural and equal rights, individualism, private property, laissez-faire, democratic republicanism, and, often, antislavery. Self-avowed and influential Loco-Focos included Herman Melville, Nathaniel Hawthorne, Walt Whitman, and countless other important figures in antebellum thought, culture, and politics ranging across the continent from New England and the northern border to the Pacific frontier zone and even the increasingly proslavery, anti-locofoco South. This study compiles the largest collection of primary sources related to the movement of any treatment to date, including dozens of newspapers, published books, poems, and pamphlets, public speeches, paintings, and private correspondence collections. This is the first and only history of the Loco-Foco Movement as such, and its conclusions offer sharp challenges to prevailing interpretations of the development of democratic-republican government, liberalism, and corporate-capitalism in the United States. While their ideology offered radical alternative models for American political and intellectual life, their efforts at practical politicking created much of the modern democratic, corporate-capitalist nation-state familiar to present-day readers

Dielectric Response of a Variable Saturated Soil Contaminated by Non-Aqueous Phase Liquids (NAPLs)

AbstractIn recent years, several studies have been conducted both in saturated and unsaturated soils to detect non-aqueous phase liquid (NAPL) hydrocarbon contamination in soils and groundwater by means of the time domain reflectometry (TDR) technique. This technique is widely used for measuring the dielectric permittivity and bulk electrical conductivity of multiphase systems. Only accurate knowledge of the dielectric response of soil matrix- water-NAPL (saturated condition) or soil matrix-air-water-NAPL (unsaturated condition) systems can allow the volumetric NAPL content (θNAPL) to be determined in the soil. This paper investigates the influence of NAPL contamination (corn oil, a non-volatile and non-toxic NAPL, was used) on TDR measurement in a volcanic soil, relating dielectric permittivity of the multiphase soil system to volumetric fluid content θf (i.e. water+NAPL). The soil samples were oven dried at 105°C and passed through a 2mm sieve. Known quantities of soil, water and oil were mixed and repacked into plastic cylinders (15cm high and 9.5cm in diameter); 40 different combinations of water and oil were tested, with θNAPL varying from 0.05 to 0.40 by 0.05cm3/cm3 increments. A volumetric mixing model with three (soil matrix-water-NAPL) or four (soil matrix-air-water-NAPL) phases permitted conversion from a dielectric permittivity domain into a θf domain. The results show that, the amount of contaminant in soil can be inferred if the total volume of pore fluid θf and the dielectric permittivity of the contaminated soil are known. Further work will be built on this initial study, concentrating on: i) enhancing the model linkage and validating it with new laboratory results; ii) validating the developed TDR interpretation tool with field results