Title
Degassing of 3H/3He, CFCs and SF6 by denitrification: Measurements and two-phase transport simulations
Author
Visser, A.
Schaap, J.D.
Broers, H.P.
Bierkens, M.F.P.
TNO Bouw en Ondergrond
Publication year
2009
Abstract
The production of N2 gas by denitrification may lead to the appearance of a gas phase below the water table prohibiting the conservative transport of tracer gases required for groundwater dating. We used a two-phase flow and transport model (STOMP) to study the reliability of 3H/3He, CFCs and SF6 as groundwater age tracers under agricultural land where denitrification causes degassing. We were able to reproduce the amount of degassing (R2 = 69%), as well as the 3H (R2 = 79%) and 3He* (R2 = 76%) concentrations observed in a 3H/3He data set using simple 2D models. We found that the TDG correction of the 3H/3He age overestimated the control 3He/3He age by 2.1 years, due to the accumulation of 3He* in the gas phase. The total uncertainty of degassed 3H/3He ages of 6 years (± 2 σ) is due to the correction of degassed 3He* using the TDG method, but also due to the travel time in the unsaturated zone and the diffusion of bomb peak 3He*. CFCs appear to be subject to significant degradation in anoxic groundwater and SF6 is highly susceptible to degassing. We conclude that 3H/3He is the most reliable method to date degassed groundwater and that two-phase flow models such as STOMP are useful tools to assist in the interpretation of degassed groundwater age tracer data. © 2008 Elsevier B.V. All rights reserved.
Subject
Geosciences
3H/3He
CFCs
Degassing
Denitrification
Groundwater dating
SF6
Two-phase transport modeling
Aquifers
Chlorofluorocarbons
Degassing
Denitrification
Fluid dynamics
Gas dynamics
Gases
Groundwater
Hydrogeology
Multiphase flow
Nitrification
Sulfur hexafluoride
Two phase flow
Underground reservoirs
H/He
CFCs
Groundwater dating
SF
Two-phase transport modeling
Helium
CFC
dating method
degassing
denitrification
hydrological modeling
measurement method
modeling
tracer
transport process
water table
chlorofluorocarbon
helium
nitrogen
sulfur hexafluoride
tritium
water
article
calibration
chemical model
chemistry
computer simulation
gas
isolation and purification
pressure
soil
Calibration
Chlorofluorocarbons
Computer Simulation
Gases
Helium
Models, Chemical
Nitrogen
Pressure
Soil
Sulfur Hexafluoride
Tritium
Water
To reference this document use:
http://resolver.tudelft.nl/uuid:08977204-139d-4c8d-935f-944ce583058b
TNO identifier
241359
ISSN
0169-7722
Source
Journal of Contaminant Hydrology, 103 (3-4), 206-218
Document type
article