Predicting the Saturated Hydraulic Conductivity of Clayey Soils and Clayey or Silty Sands

Predictive models able to provide a reliable estimate of hydraulic conductivity can be useful in various geotechnical applications. Since most of the existing predictive methods for saturated hydraulic conductivity estimation are valid only for a limited range of soils or can be applied under certain restrictive conditions, a new method applicable to clayey soils and clayey or silty sands having a wide range of values of soil index properties is proposed in this study. For this purpose, 329 saturated hydraulic conductivity values, obtained by laboratory tests carried out on different soils, were collected in a database and used to develop five equations using a multiple regression approach. Each equation correlates the hydraulic conductivity with one or more geotechnical parameters. An equation was developed that predicts, within an order of magnitude, the saturated hydraulic conductivity in the range from 1.2 × 10−11 to 3.9 × 10−6 m/s, based on simple geotechnical parameters (i.e., clay content, void ratio, plastic limit, and silt content)

nickel removal by zero valent iron lapillus mixtures in column systems

Abstract The remediation of contaminated groundwater, through permeable reactive barrier (PRB) technology, has raised strong interest in the field of environmental geotechnics. The use of granular mixtures composed of zero valent iron (ZVI) together with an inert and/or porous material is a new strategy for preventing the decrease in hydraulic conductivity of PRBs composed of pure ZVI alone. In this paper, granular mixtures composed of ZVI and lapillus in different weight ratios were tested for nickel removal through column tests. The newly proposed material, lapillus, is a low-cost material (a by-product of pumice mining), readily available and efficient for nickel removal, as is shown by the benchmark column tests carried out in this paper. The weight ratio between ZVI and lapillus, the flow velocity and the initial contaminant concentration were the factors investigated in this paper since they can strongly influence the long-term removal efficiency and hydraulic behaviour of a PRB. The column tests results were analysed in terms of hydraulic conductivity, nickel removal efficiency and the distribution of the removed nickel along the column over time. The test results clearly showed the great potential of the proposed ZVI/lapillus granular mixtures in terms of both removal efficiency and long-term hydraulic conductivity

La bonifica delle acque di falda tramite la tecnologia delle barriere permeabili reattive

A Permeable Reactive Barrier (PRB) represents a valid and sustainable in situ groundwater remediation technology. It consists of a diaphragm wall, filled with a reactive medium and placed across the flow path of the contaminated groundwater in order to intercept the contaminants.  A PRB does not require energy for, it requires the removal of modest volumes of soil, it does not present problems of visual impact and allows the use of the contaminated site during remediation. Monitoring performed on full-scale PRB, composed of zero valent iron (ZVI) as reactive medium, showed that, despite the considerable reactivity, ZVI is not able to maintain its hydraulic conductivity over a long period of time. The objective of the present work was to improve the hydraulic behaviour of the ZVI, by mixing this material with lapillus, a reactive medium of volcanic origin, sustainable for the environment and readily available. Experimental studies, conducted through batch and column tests, have shown that lapillus is reactive towards the tested contaminants, i.e. nickel and zinc, whose presence seriously  threatens the quality of aquifers. La bonifica delle acque di falda tramite la tecnologia delle Barriere Permeabili ReattiveUna barriera permeabile reattiva (BPR) rappresenta una tecnologia in situ per il risanamento delle acque di falda. Si tratta di un diaframma, costituito da un materiale permeabile e reattivo, installato nella stessa direzione del flusso di falda in maniera tale da intercettare gli inquinati contenuti in esso. Una BPR non necessita energia per il suo funzionamento, richiede la rimozione di modesti volumi di terreno, non presenta problemi di impatto visivo e consente di utilizzare il sito contaminato durante la bonifica. Monitoraggi eseguiti su BPR in vera grandezza, realizzate utilizzando ferro zero valente (Fe0) come materiale reattivo, hanno evidenziato come, nonostante la notevole reattività, esso non sia in grado di mantenere la propria conducibilità idraulica nel lungo periodo. Con l’obiettivo di migliorare le prestazioni idrauliche del Fe0, nel presente lavoro vengono presentati i risultati dei test di laboratorio effettuati per valutare la miscelazione di tale mezzo reattivo con il lapillo, un materiale di origine vulcanica, sostenibile per l’ambiente, e facilmente reperibile. Gli studi sperimentali condotti attraverso prove batch e prove di interazione in colonna, hanno dimostrato come il lapillo sia reattivo nei confronti degli inquinanti testati, ovvero nichel e zinco, la cui presenza minaccia profondamente la qualità delle falde acquifere.Una barriera permeabile reattiva (BPR) rappresenta una tecnologia in situ per il risanamento delle acque di falda. Si tratta di un diaframma, costituito da un materiale permeabile e reattivo, installato nella stessa direzione del flusso di falda in maniera tale da intercettare gli inquinati contenuti in esso. Una BPR non necessita energia per il suo funzionamento, richiede la rimozione di modesti volumi di terreno, non presenta problemi di impatto visivo e consente di utilizzare il sito contaminato durante la bonifica. Monitoraggi eseguiti su BPR in vera grandezza, realizzate utilizzando ferro zero valente (Fe0) come materiale reattivo, hanno evidenziato come, nonostante la notevole reattività, esso non sia in grado di mantenere la propria conducibilità idraulica nel lungo periodo. Con l’obiettivo di migliorare le prestazioni idrauliche del Fe0, nel presente lavoro vengono presentati i risultati dei test di laboratorio effettuati per valutare la miscelazione di tale mezzo reattivo con il lapillo, un materiale di origine vulcanica, sostenibile per l’ambiente, e facilmente reperibile. Gli studi sperimentali condotti attraverso prove batch e prove di interazione in colonna, hanno dimostrato come il lapillo sia reattivo nei confronti degli inquinanti testati, ovvero nichel e zinco, la cui presenza minaccia profondamente la qualità delle falde acquifere. Groundwater Remediation Using Permeable Reactive Barrier Technology A Permeable Reactive Barrier (PRB) represents a valid and sustainable in situ groundwater remediation technology. It consists of a diaphragm wall, filled with a reactive medium and placed across the flow path of the contaminated groundwater in order to intercept the contaminants.  A PRB does not require energy for, it requires the removal of modest volumes of soil, it does not present problems of visual impact and allows the use of the contaminated site during remediation. Monitoring performed on full-scale PRB, composed of zero valent iron (ZVI) as reactive medium, showed that, despite the considerable reactivity, ZVI is not able to maintain its hydraulic conductivity over a long period of time. The objective of the present work was to improve the hydraulic behaviour of the ZVI, by mixing this material with lapillus, a reactive medium of volcanic origin, sustainable for the environment and readily available. Experimental studies, conducted through batch and column tests, have shown that lapillus is reactive towards the tested contaminants, i.e. nickel and zinc, whose presence seriously  threatens the quality of aquifers

Optimal design of ZVI/lapillus mixtures for nickel removal in permeable reactive barriers

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Predicting the Saturated Hydraulic Conductivity of Clayey Soils and Clayey or Silty Sands

Predictive models able to provide a reliable estimate of hydraulic conductivity can be useful in various geotechnical applications. Since most of the existing predictive methods for saturated hydraulic conductivity estimation are valid only for a limited range of soils or can be applied under certain restrictive conditions, a new method applicable to clayey soils and clayey or silty sands having a wide range of values of soil index properties is proposed in this study. For this purpose, 329 saturated hydraulic conductivity values, obtained by laboratory tests carried out on different soils, were collected in a database and used to develop five equations using a multiple regression approach. Each equation correlates the hydraulic conductivity with one or more geotechnical parameters. An equation was developed that predicts, within an order of magnitude, the saturated hydraulic conductivity in the range from 1.2 × 10−11 to 3.9 × 10−6 m/s, based on simple geotechnical parameters (i.e., clay content, void ratio, plastic limit, and silt content)

A Review of the Hydraulic Performance of Permeable Reactive Barriers Based on Granular Zero Valent Iron

Permeable reactive barriers (PRBs) based on the use of zero valent iron (ZVI) represent an efficient technology for the remediation of contaminated groundwater, but the literature evidences “failures”, often linked to the difficulty of fully understanding the long-term performance of ZVI-based PRBs in terms of their hydraulic behavior. The aim of this paper is to provide an overview of the long-term hydraulic behavior of PRBs composed of ZVI mixed with other reactive or inert materials. The literature on the hydraulic performance of ZVI-based PRBs in full-scale applications, on long-term laboratory testing and on related mathematical modeling was thoroughly analyzed. The outcomes of this review include an in-depth analysis of factors influencing the long-term behavior of ZVI-based PRBs (i.e., reactive medium, contamination and the geotechnical, geochemical and hydrogeological characteristics of the aquifer) and a critical revision of the laboratory procedures aimed at investigating their hydraulic performance. The analysis clearly shows that admixing ZVI with nonexpansive granular materials is the most suitable choice for obtaining a long-term hydraulically efficient PRB. Finally, the paper summarizes a procedure for the correct hydraulic design of ZVI-based PRBs and outlines that research should aim at developing numerical models able to couple PRBs’ hydraulic and reactive behaviors

Reactive and Hydraulic Behavior of Granular Mixtures Composed of Zero Valent Iron

Zero valent iron (ZVI) is widely used in permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. The hydraulic conductivity of ZVI can be reduced due to iron corrosion processes activated by water and its constituents including pollutants. To overcome this issue, ZVI particles can be mixed with granular materials that avoid a drastic reduction in the hydraulic conductivity over time. In light of the most recent studies concerning iron corrosion processes and recalling the basic principles of century-old chemistry of iron corrosion, we have revised the results of 24 long-term column tests investigating the hydraulic and reactive behavior of granular mixtures composed of ZVI and pumice or lapillus. From this analysis, we found a clear correlation between the reactive behavior, described by the retardation factor (i.e., the ratio between flow velocity and propagation velocity of the contamination front), and the hydraulic behavior, described by means of the permeability ratio of the reactive medium (i.e., the ratio between the final and initial value of hydraulic conductivity). In particular, the permeability ratio decreased with the increase in the retardation factor. Moreover, it was found that the retardation factor is a useful parameter to evaluate the influence of flow rate, contaminant concentration, and ZVI content on the reactive behavior of the granular medium

Reactive and Hydraulic Behavior of Granular Mixtures Composed of Zero Valent Iron

Zero valent iron (ZVI) is widely used in permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. The hydraulic conductivity of ZVI can be reduced due to iron corrosion processes activated by water and its constituents including pollutants. To overcome this issue, ZVI particles can be mixed with granular materials that avoid a drastic reduction in the hydraulic conductivity over time. In light of the most recent studies concerning iron corrosion processes and recalling the basic principles of century-old chemistry of iron corrosion, we have revised the results of 24 long-term column tests investigating the hydraulic and reactive behavior of granular mixtures composed of ZVI and pumice or lapillus. From this analysis, we found a clear correlation between the reactive behavior, described by the retardation factor (i.e., the ratio between flow velocity and propagation velocity of the contamination front), and the hydraulic behavior, described by means of the permeability ratio of the reactive medium (i.e., the ratio between the final and initial value of hydraulic conductivity). In particular, the permeability ratio decreased with the increase in the retardation factor. Moreover, it was found that the retardation factor is a useful parameter to evaluate the influence of flow rate, contaminant concentration, and ZVI content on the reactive behavior of the granular medium

Reactive and Hydraulic Behavior of Permeable Reactive Barriers Constituted by Fe0 and Granular Mixtures of Fe0/Pumice

Abstract The objective of the present work is to analyze, by means of column tests, the reactivity and hydraulic long term behavior of the zero valent iron (Fe 0 ) and of a granular mixture Fe 0 /pumice, for the remediation, through the Permeable Reactive Barriers technology, of nickel contaminated groundwater. The reactive behavior was studied by analyzing nickel concentration data, through a first order kinetic model in order to determine the thickness of a hypothetical PRB and its variation over time. The hydraulic conductivity behavior was studied through a numerical-statistical geometrical model developed by the authors. Expansive iron corrosion, precipitation of reaction products and gas formation are the processes considered

Behavior of multi-layer permeable reactive barriers for groundwater remediation

This paper aims to evaluate the efficiency of a multilayer configuration of a permeable reactive barrier (PRB) made up of granular mixtures of zero valent iron (ZVI) and lapillus. The latter is a volcanic material used to disperse ZVI particles. A high dispersion of ZVI improves the long-term hydraulic conductivity but can significantly reduce reactivity due to the lower amount of ZVI. In this research, the performance of two different combinations of a two-layer configuration was studied by means of long-term column tests. The first layer, named “pre-treatment layer”, had a thickness of 4 cm and a volumetric ratio (ZVI/lapillus) of 10:90 or 05:95, while the second layer had a volumetric ratio (ZVI/lapillus) of 20:80. A single layer configuration made only of the 20:80 ZVI/lapillus was used as a benchmark. The three tests were performed using a multi-contaminated solution of copper, nickel and zinc. Test results showed an early loss of the hydraulic conductivity in the single layer configuration and an increase of PRB longevity by 68 % in the presence of the pre-treatment layer. The pre-treatment zone containing 10 % ZVI delayed the clogging phenomenon, while the zone with 5 % ZVI ensured both the correct long-term hydraulic behavior and a removal efficiency higher than 77.6 % for Nickel and 99 % for copper and zinc at 23 cm of thickness for at least two months