Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic

Gardner, W. Payton; Hokr, Milan; Shao, Hua; Balvín, Aleš; Kunz, H.; Wang, Yifeng

doi:10.1007/s12665-016-6160-x

Cited by 7 publications

(4 citation statements)

References 38 publications

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“…The modelled mean age would also be expected to change based upon the assumed age distribution (Abrams & Haitjema, 2018) as shown in Table 2. However, the similarity of the ages using the exponential and dispersion age distributions is consistent with previous work showing the mean age is relatively robust to differences in assumed age distribution (Gardner et al, 2016; Solomon et al, 2015). In Figure 7, an indication of the model sensitivity to changes in mean age of groundwater assuming an exponential mixing model in the Little Smoky River is shown.…”

Section: Discussionsupporting

confidence: 88%

Characterizing groundwater flow paths in an undeveloped region through synoptic river sampling for environmental tracers

Smerdon

Gardner

2022

Hydrological Processes

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Synoptic sampling of three rivers for a suite of environmental tracers is shown to be an efficient way to gain an understanding of groundwater flow paths for a previously unstudied large area in Alberta, Canada. For regional-scale characterization, classical hydrogeological techniques are limited by the location and number of groundwater wells. This study demonstrates that rivers can become an easily accessible location to sample the distribution of groundwater flow paths discharging to surface water.Modelling of groundwater discharge to the rivers and groundwater mean age helps generate knowledge of groundwater circulation for a large area, which is useful for conceptual model development and focusing future characterization efforts. Results indicate that the benchland areas in this region, with higher topographic relief, had hydrogeological conditions that favoured deeper groundwater circulation with a modelled mean age greater than 100 years from recharge to discharge. Lower relief areas, which coincide with a transition in bedrock formations in this region, appeared to have much shorter and shallower groundwater circulation. The approach required a field program completed in 5 days and financial budget approximately equivalent to drilling a single borehole and installing a monitoring well. It is concluded that under the right conditions, where few classical observation points exist and knowledge is limited, synoptic sampling of rivers can be used to develop scientifically defensible conceptual models at a comparable scale to regional planning and resource management.

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Section: Discussionsupporting

confidence: 88%

Characterizing groundwater flow paths in an undeveloped region through synoptic river sampling for environmental tracers

Smerdon

Gardner

2022

Hydrological Processes

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“…Inference of mean ages using LPM requires the specification of an assumed age distribution for the water sample. The true age distribution of a groundwater sample reflects mixing processes that include: convergence of groundwater flow paths caused by the architecture of the system (Leray et al., 2012), cross‐formational flow (Castro & Goblet, 2005), dispersion occurring at multiple scales (Sturchio et al., 2014; Weissmann et al., 2002), diffusive exchange in and out of mobile and immobile zones (Bethke & Johnson, 2002; Gardner et al., 2016), transience in boundary conditions (Engdahl et al., 2016; Engdahl & Maxwell, 2014), and intra‐borehole mixing that occurs in long well screen intervals during pumping (Manning et al., 2015; Visser et al., 2013). The combined influence of these processes results in age distributions that are known for idealized groundwater systems, but remain largely unknown for typical field investigations (Troldborg et al., 2008; Weissmann et al., 2002).…”

Section: Introductionmentioning

confidence: 99%

Utilizing Environmental Tracers to Reduce Groundwater Flow and Transport Model Parameter Uncertainties

Thiros

Gardner

Kuhlman

2021

Water Resources Research

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Process-based numerical models that assess and predict groundwater flow and transport are an invaluable tool for water resource management (Anderson et al., 2015), contaminated site remediation (Steefel et al., 2015), and climate change assessment (Li et al., 2017;Kollet & Maxwell, 2008). Accurate parameterizations of aquifer properties and structural characteristics that control groundwater flow and transport are fundamental components of the modeling process. Yet, natural groundwater systems are typically characterized by property heterogeneity that cannot be fully constrained using direct field measurements nor accurately extrapolated from previously studied sites. As a result, subsurface parameters used in numerical models are commonly estimated through calibration against measurements of hydraulic heads from wells and boundary fluxes (Hill & Tiedeman, 2007;Schilling et al., 2019). In the majority of cases, calibration to hydraulic data alone cannot fully constrain model parameter distributions and the resulting equifinality leads to large uncertainty in estimated aquifer properties and subsequent forecasts of interest (Anderson et al., 2015;Doherty, 2003). Joint calibration to the fluid velocity and solute transport information provided by environmental tracers has the ability to ameliorate many of the limitations and non-uniqueness in calibration to hydraulic data alone, leading to uncertainty reductions in key model parameters (Portniaguine & Solomon, 1998;Reilly et al., 1994;Sanford, 2011;Schilling et al., 2017). Despite the wide use of environmental tracer information within groundwater studies, methodologies and guidelines that optimally assimilate the information they provide into process-based numerical models are not well established (e.g., Suckow, 2014).Environmental tracers are non-applied chemical species with a broad range of input histories and/or decay/ production rates that can provide valuable solute transport information over large spatiotemporal ranges Abstract Non-uniqueness in groundwater model calibration is a primary source of uncertainty in groundwater flow and transport predictions. In this study, we investigate the ability of environmental tracer information to constrain groundwater model parameters. We utilize a pilot point calibration procedure conditioned to subsets of observed data including: liquid pressures, tritium ( 3 H), chlorofluorocarbon-12 (CFC-12), and sulfur hexafluoride (SF 6 ) concentrations; and groundwater apparent ages inferred from these environmental tracers, to quantify uncertainties in the heterogeneous permeability fields and infiltration rates of a steady-state 2-D synthetic aquifer and a transient 3-D model of a field site located near Riverton, Wyoming (USA). To identify the relative data worth of each observation data type, the post-calibration uncertainties of the optimal parameters for a given observation subset are compared to that from the full observation data set. Our results suggest that the calibration-constrained permeability field uncertainties a...

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“…This has implication for the provenience and flow path structure of the long‐residence time groundwater we observe. Further interpretation of RTDs that include diffusion processes that are salient in fractured bedrock systems (e.g., W. P. Gardner et al., 2016; Rajaram, 2021) and process‐based numerical modeling frameworks that simulate groundwater flow and transport over broad spatial and temporal scales (e.g., Thiros et al., 2021) can be powerful tools to further interrogate the source and catchment function of the observed long‐residence time fractions.…”

Section: Discussionmentioning

confidence: 99%

Constraining Bedrock Groundwater Residence Times in a Mountain System With Environmental Tracer Observations and Bayesian Uncertainty Quantification

Thiros

Siirila‐Woodburn

Dennedy‐Frank

et al. 2023

Water Resources Research

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Groundwater residence time distributions provide fundamental insights on the hydrological processes within watersheds. Yet, observations that can constrain groundwater residence times over broad timescales remain scarce in mountain catchment studies. We use environmental tracers (CFC‐12, SF6, 3H, and 4He) to investigate groundwater residence times along a hillslope in the East River Watershed, Colorado, USA. We develop a Bayesian inference framework that applies a Markov‐chain Monte Carlo (MCMC) approach to estimate noble gas recharge temperature, elevation, and excess‐air parameters and the resulting environmental tracer concentrations. MCMC is then used to propagate the environmental tracer uncertainties to estimates of groundwater mean residence times inferred with lumped parameter models. All samples contain 3H, CFC‐12, and SF6 in addition to terrigenic 4He, suggesting a mixture of water characterized by modern and premodern residence times. 4He exponential mean residence times range from hundreds of years at the upslope well to thousands of years at the toe‐slope well assuming average crustal production rates. We find that binary mixing residence time distributions with separate young and old mixing fractions are needed to predict the 4He, CFC‐12, SF6, and 3H observations, supporting the importance of flow path mixing in this bedrock system. Our findings that the fractured bedrock hosts groundwater with a mixture of residence times ranging from decades to millennia suggest variable recharge dynamics and flow path mixing along the hillslope and highlight the importance of characterizing groundwater systems with observations that are sensitive to transport over a broad range of residence times.

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Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic

Cited by 7 publications

References 38 publications

Characterizing groundwater flow paths in an undeveloped region through synoptic river sampling for environmental tracers

Characterizing groundwater flow paths in an undeveloped region through synoptic river sampling for environmental tracers

Utilizing Environmental Tracers to Reduce Groundwater Flow and Transport Model Parameter Uncertainties

Constraining Bedrock Groundwater Residence Times in a Mountain System With Environmental Tracer Observations and Bayesian Uncertainty Quantification

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