Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic
We investigated the transit time distribution (TTD) of discharge collected from fractures in the Bedrichov Tunnel, Czech Republic, using lumped parameter models and multiple environmental tracers. We then utilize time series of δ ^{18}O, δ ^{2}H and ^{3}H along with CFC measurements from individual fractures in the Bedrichov Tunnel of the Czech Republic to investigate the TTD, and the uncertainty in estimated mean travel time in several fracture networks of varying length and discharge. We also compare several TTDs, including the dispersion distribution, the exponential distribution, and a developed TTD which includes the effects of matrix diffusion. The effect of seasonal recharge is explored by comparing several seasonal weighting functions to derive the historical recharge concentration. We identify best fit mean ages for each TTD by minimizing the errorweighted, multitracer χ2 residual for each seasonal weighting function. We use this methodology to test the ability of each TTD and seasonal input function to fit the observed tracer concentrations, and the effect of choosing different TTD and seasonal recharge functions on the mean age estimation. We find that the estimated mean transit time is a function of both the assumed TTD and seasonal weighting function. Best fits as measured by themore »
 Authors:

^{[1]};
^{[2]};
^{[3]};
^{[2]};
^{[3]};
^{[4]}
 Univ. of Montana, Missoula, MT (United States). Dept. of Geosciences
 Technical Univ. of Liberec (Czech Republic)
 Federal Inst. for Geosciences and Natural Resources, Hanover (Germany)
 Sandia National Lab. (SNLNM), Albuquerque, NM (United States)
 Publication Date:
 Report Number(s):
 SAND20161766J
Journal ID: ISSN 18666280; 643719
 Grant/Contract Number:
 AC0494AL85000
 Type:
 Accepted Manuscript
 Journal Name:
 Environmental Earth Sciences
 Additional Journal Information:
 Journal Volume: 75; Journal Issue: 20; Journal ID: ISSN 18666280
 Publisher:
 SpringerVerlag
 Research Org:
 Sandia National Lab. (SNLNM), Albuquerque, NM (United States)
 Sponsoring Org:
 USDOE National Nuclear Security Administration (NNSA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 54 ENVIRONMENTAL SCIENCES
 OSTI Identifier:
 1338728
Gardner, W. Payton, Hokr, Milan, Shao, Hua, Balvin, Ales, Kunz, Herbert, and Wang, Yifeng. Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic. United States: N. p.,
Web. doi:10.1007/s126650166160x.
Gardner, W. Payton, Hokr, Milan, Shao, Hua, Balvin, Ales, Kunz, Herbert, & Wang, Yifeng. Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic. United States. doi:10.1007/s126650166160x.
Gardner, W. Payton, Hokr, Milan, Shao, Hua, Balvin, Ales, Kunz, Herbert, and Wang, Yifeng. 2016.
"Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic". United States.
doi:10.1007/s126650166160x. https://www.osti.gov/servlets/purl/1338728.
@article{osti_1338728,
title = {Investigating the age distribution of fracture discharge using multiple environmental tracers, Bedrichov Tunnel, Czech Republic},
author = {Gardner, W. Payton and Hokr, Milan and Shao, Hua and Balvin, Ales and Kunz, Herbert and Wang, Yifeng},
abstractNote = {We investigated the transit time distribution (TTD) of discharge collected from fractures in the Bedrichov Tunnel, Czech Republic, using lumped parameter models and multiple environmental tracers. We then utilize time series of δ18O, δ2H and 3H along with CFC measurements from individual fractures in the Bedrichov Tunnel of the Czech Republic to investigate the TTD, and the uncertainty in estimated mean travel time in several fracture networks of varying length and discharge. We also compare several TTDs, including the dispersion distribution, the exponential distribution, and a developed TTD which includes the effects of matrix diffusion. The effect of seasonal recharge is explored by comparing several seasonal weighting functions to derive the historical recharge concentration. We identify best fit mean ages for each TTD by minimizing the errorweighted, multitracer χ2 residual for each seasonal weighting function. We use this methodology to test the ability of each TTD and seasonal input function to fit the observed tracer concentrations, and the effect of choosing different TTD and seasonal recharge functions on the mean age estimation. We find that the estimated mean transit time is a function of both the assumed TTD and seasonal weighting function. Best fits as measured by the χ2 value were achieved for the dispersion model using the seasonal input function developed here for two of the three modeled sites, while at the third site, equally good fits were achieved with the exponential model and the dispersion model and our seasonal input function. The average mean transit time for all TTDs and seasonal input functions converged to similar values at each location. The sensitivity of the estimated mean transit time to the seasonal weighting function was equal to that of the TTD. These results indicated that understanding seasonality of recharge is at least as important as the uncertainty in the flow path distribution in fracture networks and that unique identification of the TTD and mean transit time is difficult given the uncertainty in the recharge function. But, the mean transit time appears to be relatively robust to the structural model uncertainty. The results presented here should be applicable to other studies using environmental tracers to constrain flow and transport properties in fractured rock systems.},
doi = {10.1007/s126650166160x},
journal = {Environmental Earth Sciences},
number = 20,
volume = 75,
place = {United States},
year = {2016},
month = {10}
}