Solute transport in crystalline rocks at Aspo; I, Geological basis and model calibration

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doi: 10.1016/S0169-7722(02)00137-7
Authors:Mazurek, Martin; Jakob, Andreas; Bossart, Paul
Author Affiliations:Primary:
University of Bern, Institute of Geological Sciences, Bern, Switzerland
Other:
Paul Scherrer Institute, Switzerland
Geotechnical Institute, Switzerland
Volume Title:8th international conference on Chemistry and migration behaviour of actinides and fission products in the geosphere; Migration '01
Volume Authors:Kim, Jae-Il, editor; Geckeis, Horst
Source:Journal of Contaminant Hydrology, 61(1-4), p.157-174; 8th international conference on Chemistry and migration behaviour of actinides and fission products in the geosphere; Migration '01, Bregenz, Austria, Sept. 16-21, 2001, edited by Jae-Il Kim and Horst Geckeis. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0169-7722
Publication Date:2003
Note:In English. 18 refs.; illus., incl. 1 table
Summary:Water-conducting faults and fractures were studied in the granite-hosted Aspo Hard Rock Laboratory (SE Sweden). On a scale of decametres and larger, steeply dipping faults dominate and contain a variety of different fault rocks (mylonites, cataclasites, fault gouges). On a smaller scale, somewhat less regular fracture patterns were found. Conceptual models of the fault and fracture geometries and of the properties of rock types adjacent to fractures were derived and used as input for the modelling of in situ dipole tracer tests that were conducted in the framework of the Tracer Retention Understanding Experiment (TRUE-1) on a scale of metres. After the identification of all relevant transport and retardation processes, blind predictions of the breakthroughs of conservative to moderately sorbing tracers were calculated and then compared with the experimental data. This paper provides the geological basis and model calibration, while the predictive and inverse modelling work is the topic of the companion paper [J. Contam. Hydrol. 61 (2003) 175]. The TRUE-1 experimental volume is highly fractured and contains the same types of fault rocks and alterations as on the decametric scale. The experimental flow field was modelled on the basis of a 2D-streamtube formalism with an underlying homogeneous and isotropic transmissivity field. Tracer transport was modelled using the dual porosity medium approach, which is linked to the flow model by the flow porosity. Given the substantial pumping rates in the extraction borehole, the transport domain has a maximum width of a few centimetres only. It is concluded that both the uncertainty with regard to the length of individual fractures and the detailed geometry of the network along the flowpath between injection and extraction boreholes are not critical because flow is largely one-dimensional, whether through a single fracture or a network. Process identification and model calibration were based on a single uranine breakthrough (test PDT3), which clearly showed that matrix diffusion had to be included in the model even over the short experimental time scales, evidenced by a characteristic shape of the trailing edge of the breakthrough curve. Using the geological information and therefore considering limited matrix diffusion into a thin fault gouge horizon resulted in a good fit to the experiment. On the other hand, fresh granite was found not to interact noticeably with the tracers over the time scales of the experiments.While fracture-filling gouge materials are very efficient in retarding tracers over short periods of time (hours-days), their volume is very small and, with time progressing, retardation will be dominated by altered wall rock and, finally, by fresh granite. In such rocks, both porosity (and therefore the effective diffusion coefficient) and sorption Kds are more than one order of magnitude smaller compared to fault gouge, thus indicating that long-term retardation is expected to occur but to be less pronounced. Abstract Copyright (2003) Elsevier, B.V.
Subjects:Aquifers; Boreholes; Calibration; Controls; Diffusivity; Experimental studies; Faults; Geometry; Granites; Igneous rocks; Matrix; Migration of elements; Mobility; Models; Plutonic rocks; Pollution; Prediction; Preferential flow; Radioactive waste; Solute transport; Theoretical models; Tracers; Transport; Underground installations; Waste disposal; Aspo Hard Rock Laboratory; Europe; Kalmar Sweden; Scandinavia; Sweden; Western Europe
Record ID:2003043702
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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