High Performance Simulation of Environmental Tracers in Heterogeneous Domains

Abstract

In this study, we use PFLOTRAN, a highly scalable, parallel, flow, and reactive transport code to simulate the concentrations of 3H, 3He, CFC-11, CFC-12, CFC-113, SF6, 39Ar, and the mean groundwater age in heterogeneous fields on grids with an excess of 10 million nodes. We utilize this computational platform to simulate the concentration of multiple tracers in high-resolution, heterogeneous 2D and 3D domains, and calculate tracer-derived ages. Tracer-derived ages show systematic biases toward younger ages when the groundwater age distribution contains water older than the maximum tracer age. The deviation of the tracer-derived age distribution from the true groundwater age distribution increases with increasing heterogeneity of the system. However, the effect of heterogeneity is diminished as the mean travel time gets closer to the tracer age limit. Age distributions in 3D domains differ significantly from 2D domains. 3D simulations show decreased mean age, and less variance in age distribution for identical heterogeneity statistics. High-performance computing allows for investigation of tracer and groundwater age systematics in high-resolution domains, providing a platform for understanding and utilizing environmental tracer and groundwater age information in heterogeneous 3D systems.

Beyond Classical Observations in Hydrogeology: The Advantages of Including Exchange Flux, Temperature, Tracer Concentration, Residence Time, and Soil Moisture Observations in Groundwater Model Calibration

“…Like direct observations of C, the integration of observations of TT between two discrete points within a GW flow system into the calibration of an IFM is relatively straightforward and under favorable conditions (i.e., under predominantly advective transport) can be done with an advective flow tracking scheme rather than with explicit advection‐dispersion‐based mass transport and RT simulations. Compared to the direct use of observations of C, however, using observations of RT (and to a lesser extent of TT) for IFM calibration is less straightforward and harbors the danger of introducing a bias toward younger RT, as most natural environmental tracers are limited in the coverage of RTs (Gardner et al, ; McCallum et al, , ; Sanford, ): Once the maximum estimable RT of a tracer is reached by at least some fraction of the sampled water, the additional time spent in the subsurface is not identifiable by that tracer anymore, and the estimated apparent GW age thus often appears too young. For systems where high GW ages are expected and where the applied tracers do not cover all expected RT, directly simulating the (reactive) transport of the tracer used for calibration is recommended rather than using simpler flow and particle tracking approaches (McCallum et al, ).…”

Air warming trends linked to permafrost warming in the sub-Arctic catchment of Tarfala, Sweden

“…The numerical simulation experiments are conducted using the well-established code PFLOTRAN (Hammond et al 2012), which solves multiphase flow, heat and transport equations and has had a wide range of applications within hydrogeology (Gardner et al 2015;Tutolo et al 2015). In this study, the recently developed extension PFLOTRAN-ICE for problems involving heat and water flow in partially frozen ground is used.…”

Physical and Chemical Controls on the Simultaneous Occurrence of Young and Old Groundwater Inferred From Multiple Age Tracers

“…While mixing models are well developed in the literature, an important shortcoming is that they do not explicitly simulate physical mixing mechanisms and therefore potentially allow for physically unrealistic scenarios. To date, only few studies have sought to employ process‐based models to more closely interrogate measured field data of multiple environmental tracers and to investigate how various types of physical transport mechanisms can affect interpreted groundwater ages (Cook et al, ; Gardner et al, ; McCallum et al, ). Therefore, this study systematically explores and discusses the influence of different physical transport processes on generating mixing between young and old groundwater and to what extent they can contribute to field‐observed apparent age discrepancies.…”