Hostname: page-component-76fb5796d-qxdb6 Total loading time: 0 Render date: 2024-04-27T10:49:09.654Z Has data issue: false hasContentIssue false
  • English
  • Français

Intrusion of Seawater into a Porous Fracture zone a Coupled Geohydrochemical Modelling Exercise

Published online by Cambridge University Press:  25 February 2011

Veijo O. Pirhonen
Veijo O. Pirhonen*
Affiliation:
Technical Research Centre of Finland, P.O. BOX 108, SF-02151 Espoo, Finland.
Get access

Abstract

A coupled geochemical transport program PHREEQM2D has been tested in order to examine intrusion of seawater into fracture zones which can be connected to tunnels, such as nuclear-waste repositories on the sea shores. The code consists of a flow and transport program HST2D and a chemical equilibrium program PHREEQE. It uses a mixing cell approach, where chemistry and transport are solved separately. Ion exchange is calculated by means of a simple surface complexation model.

In the present artificial exercise, replacement of groundwater by seawater in a connecting porous fracture zone was modelled without comparing the results to observed data. Dilution, mixing, ion exchange, and dissolution/precipitation reactions were examined.

The results of modeling showed that the sulphate front of seawater moved some distance towards the tunnel during the simulations. The characteristic solutes of dilute groundwater were assumed to enter the tunnel in a short period of time. Amounts of sulphates decreased due to dilution and mixing. The chemical contents of waters were also affected by dissolution, precipitation, and ion exchange. Calcite dissolved and oxyhydroxides precipitated in oxidizing water. The strongest exchangeable ions in water, Ca and Na, were retarded due to ion exchange in the mixing zones. This caused an increase in dissolution of calcite in the mixing zones. Calcite would, however, start to precipitate in the mixing zone when the ion exchange capacity of rock would be consumed.

Some important factors, such as retardation on oxide surfaces (adsorption models) and microbial activity (organic complexation models) have not been tested in the present exercise. Otherwise, the PHREEQM2D showed its applicability to modelling of chemical equilibrium, dilution, mixing, ion exchange, and elution/precipitation in discrete porous zones in transient conditions. It could be used to model temperature-enchanced, coupled geohyd-Γochemical, processes in porous zones consisting of densely fractured or crushed crystalline rock.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 333: Symposium V – Scientific Basis for Nuclear Waste Management XVII , 1993 , 811
Copyright
Copyright © Materials Research Society 1994

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1 Appelo, C.A.J. and Postma, D., Geochemistry, groundwater and pollution (Balkema 1992), p. 500.Google Scholar
2 Appelo, C.A.J. and Willemsen, A., Geochemical calculations and observations on salt wa ter intrusions, I: A combined geochemical/mixing cell model. J. Hydrol. 94, 313–330 (1987).CrossRefGoogle Scholar
3 Banwart, S., Gustafsson, E., Laaksoharju, M., Nilsson, A-C., Tulborg, E-L. and Wallin, B., redox processes in granitic coastal aquifer: Characterization of the large scale experimental site and some initial results. SKB, Progress Report 25-93-03, 1993.Google Scholar
4 Beekman, H.E., Ion-chromatography of fresh- and seawater intrusion, PhD thesis, Free University Amsterdam, 1992.Google Scholar
5 Cederberg, G.A., Street, R.L. and Leckie, J.O., A groundwater mass transport and chemistry equilibrium model for multicomponent system, Water Resour. Res., 21 (8), 1095–1104 (1985).CrossRefGoogle Scholar
6 Hagoort and Associates - HST2D - PC version 2.0. Heat and solute transport simulator for personal computers - Users manual. Hagoort and Ass. Delft, The Netherlands, 22, 1992.Google Scholar
7 Jauzein, M.C. , Andre, C., Magrita, R., Sardin, M., and Sweick, D., A flexible computer co de for modeling transport in porous media, Impact Geoderma 44, 95–113 (1989).CrossRefGoogle Scholar
8 Kipp, K.L., HST3D - A computer code for simulation of heat and solute transport in three-dimensional groundwater flow systems. USGS - Water Resor. Inv. Report 86-4095, 1987.Google Scholar
9 Parkhurst, D.L., Thorstenson, D.C. and Plummer, L.N., PHREEQE - A computer pro gram for geochemical calculations, USGS Water Resour. Inv. Report 80-96, 1980.Google Scholar
10 Willemsen, A., PHREEQM-2D - PHREEQE in a multicomponent mass transport model coupled to HST2D, Manual and users guide, IF Technology, Arnhem, The Netherlands.Google Scholar
11 Willemsen, A. and Pirhonen, V., Calculation of adsorption with the diffuse layer model, constant capacitance model and triple layer model in PHREEQM-2D, VTT Technical Research Centre of Finland, VTT-TGL Report LOKA 7/93, 1993.Google Scholar