Abstract
Dye tracing is an efficient method for spring watershed delineation, but is also used in surface waters to assess pollution migration over several kilometers. The aim of this study is to develop a simple and parsimonious approach that accounts for a linear relationship between dispersivity and scale that could be used for the simulation of large-scale transport processes in aquifers. The analysis of 583 tracer recoveries is used to validate an inverse relationship between arrival time and peak concentration, which is shown to be a consequence of the linear relationship between dispersivity and scale. These results show that the tracer displacement through a given tracing system can be characterized at a large scale by a constant Peclet number. This interpretation is used to propose a new approach for tracer test design based on the analytical expression of the peak/time factor. It is also used for Peclet number assessment and simulation of the whole tracer residence-time distribution using a new method based on the ratio between the mode of the residence time distribution (hmod) and the corresponding time from injection (tmod), which is called the hmod/tmod method. This methodology is applied to two tracer tests carried out in a karst aquifer over 13 km between the same injection and detection points under distinct hydrological conditions. These results found practical applications in generalizing tracer test results to various flow conditions, or guiding the parameterization of physically-based vulnerability mapping methods.
Highlights
Quantitative analyses of tracer tests provide direct information on processes that control the migration of contaminants
This work shows how a linear-scale effect in dispersive media can be implemented in a 1D advection-dispersion framework for a better representation of large-scale transport processes
Results based on 583 tracer tests show that Pe can be used as an intrinsic parameter of the tracing system, without scaledependence
Summary
Quantitative analyses of tracer tests provide direct information on processes that control the migration of contaminants Such techniques have been widely applied in surface water and groundwater hydrology to describe transport processes and assess the vulnerability of rivers or aquifers to contamination, which is of primary importance when considering the protection and management policies of water resources. Dye tracing is a very effective technique for delineating catchment areas of springs or wells, but the quantitative results of large-scale tracer tests are often poorly exploited in engineering reports. This method would be useful for the parameterization of physically based vulnerability mapping methods, especially in karstified environments (Dedewanou et al 2015; Popescu et al 2019). Labat and Mangin (2015) show how an inverse Laplace-transform procedure applied to a tracer RTD can be used to distinguish a quick-flow advection-dominated component from a slow-flow advection–dispersion/dominated component in a karstic aquifer
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