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The migration of a groundwater contaminant plume consisting of light nonaqueous phase liquids (LNAPLs) along the Ionian coastline of Sicily, Italy, has been reported to follow a trajectory that is inconsistent with the regional hydraulic gradient. The influence of several faults affecting the fractured carbonate bedrock aquifer, and groundwater abstraction from a well, were hypothesized to be responsible for the anomalous trajectory of the contaminant plume. A conceptual hydrogeological model was developed for the study area that incorporated structural information derived from geophysical surveys and the mapping of fractures in bedrock outcrops. This conceptual model was incorporated into numerical groundwater flow and solute transport models to simulate the groundwater transport of the light nonaqueous phase liquids. Four model scenarios representing different levels of complexity were tested to assess the relative influence of geological heterogeneity and groundwater abstraction on the migration of the contaminant plume. Results show that underground major discontinuity systems, invoking the presence of the faults in the model domain accounted for the observed migration of the contaminant plume, act as conduits for groundwater flow. Conversely, groundwater abstraction from a well was found to result in relatively minor, localized impacts to the migration of the contamination plume. This study demonstrates the importance of incorporating geological heterogeneity into groundwater modelling and environmental risk assessments associated with the storage of LNAPLs. [ABSTRACT FROM AUTHOR]

Abstract: Solute transport in rivers and streams with hyporheic zone exchange and/or in-stream storage is typically affected by the prevailing flow rate. The research reported here focuses on stream tracer experiments repeated many times along the same Austrian (Mödlingbach) and Italian (Torrente Lura) channel reaches to characterize parameter dependency on flow rate. Both groups of data sets showed an increase of storage zone area and main stream area with discharge. In either case, a strong negative correlation was obtained between storage zone residence time and flow rate. From the Mödlingbach data, no clear relationship with Q emerged for the dispersion coefficient and the dead zone ratio, whereas Torrente Lura showed a clear positive correlation of the dispersion coefficient with the flow rate and a slightly negative Q-dependency for the dead zone ratio. Mödlingbach and Torrente Lura results are presented against the background of other repeat experiments reported in literature. In practical applications, the computation of peak concentrations frequently rests on the transfer of transport parameters from one flow rate to another. Using the above Austrian and Italian data sets it was shown that the errors in simulated Mödlingbach peak concentrations remain within a 40% margin, if the ratio of flow rates (for calibration and simulation, resp.) does not exceed 2:1. With Torrente Lura, parameter transfer resulted in somewhat lower peak errors. [ABSTRACT FROM AUTHOR]

La heterogeneidad de las facies en escala de los niveles litológicos individuales controla, a escala macroscópica, el flujo de agua y el transporte de contaminantes en los sedimentos porosos. En particular la presencia de aspectos organizados, tales como niveles permeables conectados, tienen un efecto significativo en los tiempos de tránsito y dispersión. Aquí, se estudian los efectos de la heterogeneidad de las facies sobre el flujo y transporte para tres bloques, cuyo volumen es del orden de un metro cúbico, excavados en sedimentos aluviales en el valle de Ticino (Italia). Usando los resultados de trazadores de experimentos numéricos sobre estos dominios, se calcula el coeficiente de dispersión longitudinal con una aproximación Euleriana basada en el ajuste de las curvas de rupturas con la solución analítica de la ecuación de transporte convectiva - dispersiva. Además, se calcula el tensor de dispersión con una aproximación Lagrangiana a partir de momentos de Segundo orden de la distribución de las partículas. Se testearon tres tipos de indicadores de conectividad: (1) la función de conectividad; (2) flujo, transporte y conectividad estadística; (3) indicadores originales de conectividad de las facies (intrínseco, normal y total). La función de conectividad provee la información más completa. Algunos de los indicadores de transporte y de conectividad estadística se correlacionan la dispersividad. El análisis simultáneo de los tres indicadores de conectividad de las facies enfatiza los aspectos geométricos fundamentales que controlan el transporte. [ABSTRACT FROM AUTHOR]

Summary: In this paper the mechanisms determining the mobilization and transport of solutes driven by rainfall through runoff pathways at catchment scales are investigated through the analysis of tracer experiments. The hydro-chemical response of a small catchment in Northern Italy has been monitored in continuous during 4 weeks by properly measuring rainfall rates, streamflows and stream flux concentrations. The chemical response has been analyzed by employing two different tracers: nitrates from diffuse agricultural sources and lithium from a point injection (Li+). A modelling exercise simulating the observed hydro-chemical response of the test catchment has also been carried out. Inferences from the comparative analyses prove instructive, in particular concerning the scaling of mobilization processes and the age of runoff water. Indeed, the interactions between old and new water were found to be central to understand the mechanisms driving the transfer of solutes and pollutants from soil to stream water. The modeling exercises also evidenced the noteworthy potential of the formulation of transport by residence time distributions to describe large scale solute transport processes. [Copyright &y& Elsevier]