TECHNICAL REPORT 85-55 - Nagra · RESUME Trois diaclases (fissures) ... Hydraulikversuchen, unter...

Nagra Nationale Genossenschaft fUr die Lagerung radioaktiver Abfalle

Cedra Societe cooperative nationale pour l'entreposage de dechets radioactifs

·Cisra Societa cooperativa nazionale per l'immagazzinamento di scorie radioattive

TECHNICAL REPORT 85-55

Final Report of the Migration in a Single Fracture -Experimental results and evaluation

H. Abelin I. Neretnieks S. Tunbrant L. Moreno

May 1985

Royal Institute of Technology, Stockholm, Sweden

Parkstrasse 23 5401 Baden/Schweiz Telephon 056/20 55 11

Das Stripa-Projekt ist ein Projekt der Nuklearagentur der OECD. Unter internationaler Beteiligung werden von 1980-86 Forschungsarbeiten in ei nem un teri rdi schen Fe 1 s 1 a bor in Schweden durchgeführt. Di ese so 11 en die Kenntnisse auf folgenden Gebieten erweitern: - hydrogeologische und geochemische Messungen in Bohrlochern - Ausbreitung des Grundwassers und Transport von Radionukliden durch

Klüfte im Gestein - Verhalten von Materialien, welche zur Verfüllung und Versiegelung von

Endlagern eingesetzt werden sallen - Methoden zur zerstorungsfreien Ortung von Storzonen im Fels Seitens der Schweiz beteiligt sich die Nagra an diesen Untersuchungen. Die technischen Berichte aus dem Stripa-Projekt erscheinen gleichzeitig in der NTB-Serie der Nagra.

The Stripa Project is organised as an autonomous project of the Nuclear Energy Agency of the OECD. In the period from 1980-86, an international cooperative programme of investigations is being carried out in an underground rock laboratory in Sweden. The aim of the work is to improve our knowledge in the following areas: - hydrogeological and geochemical measurement methods in boreholes - flow of groundwater and transport of radionuclides in fissured rock - behaviour of backfilling and sealing materials in a real geological

environment - non-destructive methods for location of disturbed zones in the rock Switzerland is represented in the Stripa Project by Nagra and the Stripa Project technical reports appear in the Nagra NTB series.

Le projet Stripa est un projet autonome de 1 'Agence de 1 'OCDE pour 1 • Energie Nue 1 éa ire. Il s • agit d • un programme de recherche avec participation internationale, qui sera réalisé entre 1980 et 1986 dans un laboratoire souterrain, en Suède. Le but de ces travaux est d'améliorer et d'étendre les connaissances dans les domaines suivants: - mesures hydrogéologiques et géochimiques dans les puits de forage - chimie des eaux souterraines à grande profondeur - écoulement des eaux sou terrai nes et transport des ra di onu cl éi des dans

les roches fracturées - comportement des maté ri aux de colmatage et de scellement des dépôt

finals - méthodes de localisation non destructive des zones de perturbation de

1 a roche La Suisse est représentée dans le projet Stripa par la Cédra. Les rapports techniques du projet Stripa sont publiés dans la série des rapports techniques de la Cédra (NTB).

- I -

ABSTRACT

Three fractures in granitic rock have been investigated by hydraulic

testing and by migration tests with nonsorbing as well as with sorbing

tracers. The sorbing tracers were Cs, Sr, Eu, Nd, Th and U.

The fractures are located in drifts at 360 m depth in the Stripa mine

in mid Sweden. The fractures are clearly visible in the drifts. There

is natural water flow in the fractures. Injection took place at 5-10 m

distance from the roof of the drifts. The water was collected at 10-15

locations on every fracture as it intersects the drift. Injection and

collection of water was done during more than 7 months in one of the

fractures. The fracture where the sorbing tracers were injected was

excavated after the test and the surface of the fracture was analysed

for the tracers. The tracers were also analysed for, to a depth of up

to 5 mm in the rock matrix.

The results show that there is distinct channelling in the plane of

the fractures. The channels make up 5-20 % of fracture. The fissure

(or channel) widths are much (order(s) of magnitude) larger than what

can be deduced from hydraulic testing assuming laminar flow in a

smooth slit.

None of the sorbing tracers arrived at the collection points with the

water. The sorbing tracer Sr migrated less than was originally

expected. Cs, Eu, and U were found in highest concentrations very near

the inject ion point. Nd and Th could not be found on the fracture

surface because of the high natural background.

- II -

RESUME

Trois diaclases (fissures) de la roche granitique ont fait 1 'objet

d•essais hydrauliques et de tests de migration, à l'aide de traceurs

tant sorbants que non sorbants. On a pris pour traceurs sorbants Cs, Sr,

Eu, Nd, Th et U.

Les diaclases sont localisées dans des galeries situées à 360 rn de

profondeur dans 1 a mi ne de Stri pa, au centre de 1 a Suède. Elles sont

clairement visibles dans les galeries. On observe un écoulement d'eau

naturel dans ces diaclases. L'injection des traceurs a eu lieu entre 5

et 10 rn du toit des galeries .. L'eau a été recueillie en 10 à 15 points

de chaque diaclase coupant la galerie. On a procédé à l'injection et à

la récupération de l'eau dans l'une des diaclases, pendant plus de 7

mois. Après 1 'essais, la diaclase où les traceurs sorbants ont été

injectés a été excavée et sa teneur en traceurs analysée, cel a jusqu 1 à

une profondeur de maximum 5 mm à 1 'intérieur de la matrice rocheuse.

Les résultats montrent qu 1 i 1 existe une canalisa ti on distincte dans 1 e

plan des diaclases. Ces canaux constituent 5 à 20 % de la surface de la

diaclase. Les largeurs des fissures (ou canaux) sont beaucoup plus

(ordre(s) de magnitude) importantes que ce qui peut être déduit de

1 • essai hydraulique qui assume un écoulement 1 ami nai re dans une fente

nette ..

Aucun des traceurs sorbants n'est parvenu jusqu'aux points où 1 'eau

était recueillie. Le traceur sorbant Sr a moins migré qu 1on ne s'y

attendait initialement. Cs, Eu et U ont été trouvés en concentrations

très élevées tout près du point d 1 injection. Nd et Th n'ont pu être

décelés à la surface de la diaclase, en raison des concentrations

naturelles élevées.

- III -

ZUSAMMENFASSUNG

Drei Klüfte (Spalten) in granitischem Gestein wurden mit Hydraulik- und

Migrationsversuchen mit sorbierenden und nichtsorbierenden Tracern unter

sucht. Die sorbierenden Tracer waren Cs, Sr, Eu, Nd, Th und U.

Die Klüfte befinden sich in Stollen in einer Tiefe von 360m in der

Stripa Mine in Zentralschweden. Die Klüfte sind klar sichtbar in den

Stollen. In den Klüften existiert eine natürliche Wasserströmung. Die

Injektionen erfolgten in einem Abstand von 5-10 m vom Stollendach. Das

Wasser wurde an je 10-15 Stellen, jeweilen dort wo die Klüfte den

Stollen durchschlagen, gesammelt. Wasser-Injektion und -Sammlung

erfolgte während mehr a 1 s 7 Monate in einer der Klüfte. Die Kluft, in

we 1 ehe die sorbi erenden Tracer i nj i ziert wurden, wurde nach dem Versuch

ausgebrochen und die Kluftoberfläche nach Tracern untersucht. Die

Gesteinsmatrix wurde auch bis in eine Tiefe von 5 mm nach Tracern

untersucht.

Die Ergebnisse zeigen eine deutliche Kanalisierung in der Kluftebene.

Die Kanäle decken 5-20 % der Kluftoberfläche. Die Spa 1 t

(Kanal) -Öffnungen sind viel grösser (um Grössenordnungen) als von

Hydraulikversuchen, unter der Annahme eines 1 ami naren Flusses in einem

glatten Spalt, abgeleitet werden kann.

Keiner der sorbierenden Tracer erreichte die Sammelstelle. Der sor

bierende Tracer Sr wanderte weniger als zuerst erwartet. Die höchsten

Konzentrationen an Cs, Eu und U wurden in unmittelbarer Nähe der

Injektionsstelle gefunden.

Konzentrationen konnten Nd

festgestellt werden.

Aufgrund

und Th auf

der

der

hohen natürlichen

Kluftoberfläche nicht

TABLE OF CONTENTS

SUMMARY 1 BACKGROUND 2 PURPOSE

3 EXPERIMENTAL DESIGN 3.1 General

- IV -

3.2 The preparatory investigation 3.3 The main investigation

4 INSTRUMENTATION AND SITE PREPARATION 4.1 Water flow monitoring 4.2 Site preparation 4.3 Location of injection points 4.4 Pressure pulse tests

4.5 Equipment, injection of tracers 4.6 Water collection

3

4

4

6

6

10 10 10 11 12

12

14

4.7 Excavation of the fracture 14

5 MODELLING 16

5.1 Modelling of flow and pressure pulse tests 16

5.2 Modelling of tracer movement 21

6 RESULTS 36 6.1 Pressure pulse testing 36 6.2 Water flow monitoring 37 6.3 Conservative tracer runs 38

6.4 Calculation of fracture widths 46 6. 5 Sorbing tracer runs 53 6.6 Comparisons between models and experiments 68

7 DISCUSSION 84 7.1 Experimental design 84 7.2 Pressure pulse testing 7.3 Conservative tracer movement 7.4 Fracture widths 7.5 Dispersion

85

86 86 88

7.6 Sorbing tracer movement 89

7.7 Modelling 90 7.8 Concepts of water flow within a fracture 93

8 CONCLUSIONS 96 9 REFERENCES 98

10 NOTATION 101

- v -

APPENDICES

1 Location of fractures 2 Location of sampling holes at the main test site 3 Evaluation of the integral in the advection-dispersion-

matrix diffusion model

103

104

105

4 Pressure responses and water loss rates 107

5 Tables with results from pressure pulse tests 111

6 Data on main cores and fractures 115

7 Number of sample cores taken and analyses performed 119

8 Tracer concentration in samples from the water collecting holes 120

9 Surface concentration data 121

10 Concentration variation with depth 131

11 Mineral analysis 142

12 Pre-injection concentration (background) 145

13 Determination of the effective diffusivity 149

14 Test of carry-over between samples being ground off 151

15 Channeling within fracture A 155

- VI -

SUMMARY OF RESULTS

Experimental design and instrumentation

The equipment has worked very well with the exception of the varia

tions of the injection flow rates. The tracers Uranine and Iodide were

injected simultaneously in the same flow path. They behaved identically indicating that they do not react with the rock. All the

dyes except Uranine coloured the nylon tubing used in the experiment

but the loss due to this effect is insignificant.

Hydraulic pulse testing

The hydraulic pulse testing has shown that even though some of the

injection holes were separated only 0.5 m the response to the pressure

pulses could vary considerably. This clearly shows that fracture properties are not constant over the fracture plane.

Water flow monitoring

The water flow was monitored in three fissures at totally some 40

sectionse Water flowed only in a minor part of the sections. Flowing

parts were divided from each other by nonflowing parts. These channels

make up between 5 and 20 % of the fissures.

Conservative tracer injections

The breakthrough curves also show, that sever a 1 d i st i net channe 1 s are present. This information and the information from the monitoring of

the water flow rates from the fractures used, in the preliminary and the main experiment, clearly shows that channelling within a single

fracture exists.

- VII -

Fracture widths

The hydraulic pulse testing, water flow monitoring and observations of the tracer reside nee times show that the fracture width determined

from water residence times and flow rates is much larger (order(s) of magnitude) than the equivalent fracture width which would cause the

pressure drop in laminar flow in a slit. Hydraulic tests will thus not give any direct information on actual flow porosity.

Flow geometry within a single fracture

The flow is very unevenly distributed along the fissure planes investigated. Large areas do not carry any water. The water flows in

channels which seem to be 10-100 em wide. The channels make up only 5-20 % of the fracture p 1 an e. There was at 1 east one connection

between two of the channels investigated over a distance of 4.5 m. Channel widths (openings) are considerably larger than the equivalent channel width for pressure drop between two parallel plates.

Sorbing tracer movement

Elevated concentrations of the sorbing tracers Cs, Sr, Eu, Nd, U have

been found on the fracture surface as well as in depth in the adjacent

rock matrix (Cs, Sr, Eu, Nd). The concentration was highest near the injection hole. The obtained concentration profiles in depth may to some extent be due to a rough fracture surface. The penetration depths found for Cs and Sr go much deeper than the surf ace roughness. This indicates that the retarding mechanisms, such as matrix diffusion and sorption, found in laboratory experiments also exist in a real environment. It has not been possible to fully quantify these retarding mechanisms in this experiment but the results are consistent with the results from the laboratory experiments. The retardation of

Sr was stronger than originally expected. This could be due to higher

Kd values than expected or due to a much larger surface area in contact with the flowing water. This enlargement of the surface could

- VIII -

be due to clay infillings in the fracture or because the fracture has split up to several thinner fractures which are joined together again before entering the drift.

Modelling

The output from a model is very dependent on the assumed flow geometry of the fracture. Trying to add channelling to the model without the

poss i bi 1 ity to determine these extra parameters by independent means will just give a better fit of the model to the experimental data

without adding any useful information. The fracture 11 width 11 can be varied by assuming different breadth of the channel/s. All the modelling is based on the assumption that the injected tracers are mixed with all the water flow at the injection point and not somewhere between injection point and sampling point. This together with the

fact that the fracture breadth is unknown along the flow path makes

the determination of actual fracture widths inaccurate.

Of the three different mode 1 s tested for tracer transport the one which does not account for matrix diffusion cannot explain the observed penetration in depth of the sorbing tracers. The two other models differ mainly in the way they account for dispersion. One assumes Fi ck ian dispersion, the other assumes pure channe 11 i ng, but both include matrix diffusion. Available data are not sufficient to firmly conclude which of the mechanisms is mainly responsible for

dispersion. The presence of channels does, however, indicate that 11 Channelling dispersion .. may not be negligible.

It has not been possible to quantitatively fit the models to the observed date because of the large variations in sorbed concentration over the fissure surface. The variation is due to channelling as well as to variations in mineralogy on the surface. The observed data fall within those which may be expected from independent laboratory investigations and do not contradict previous results.

1

1 BACKGROUND

In a final repository for radioactive waste in crystalline rock, water flowing in the fractures may transport the radionucl ides eventually leached from the waste. To be able to predict the migration of the radionuclides the processes involved must be understood. To quantify the processes, data from flow and transport in real fractures under realistic conditions are needed. fviodels used for prediction must

include descriptions of the important processes and mechanisms.

Most previous studies concerning water flow in rocks are based on the assumption that the water flow can be described as porous media flow.

This might be true for very large distances where the flow would encounter a multitude of fractures, and some averaging may be conceiv

able at the scale considered.

Transport over short distances, i.e. in the vicinity of the canister, most probably occurs in individual fractures. On an intermediate scale

where more than a few fractures conduct the flow, well-type tracer tests alone cannot give the detailed information needed to understand

dispersion and sorption phenomena in fissured rock. Actual tracer

tests are needed to obtain data on pathways and flow porosities. Tests with sorbing tracers are needed to compare predictions based on models and laboratory data, i.e. to validate the transport models.

The migration modelling in the safety analysis for a repository in granitic rock is based on the assumption that if and when any radionuclides are leached from the waste, practically all of the important

rad i onuc 1 ides wi 11 interact chemically or physically with the bedrock and will thereby be considerably retarded. The magnitude of this

retardation depends upon the flow rate of the water, the uptake rates and equilibria of the reactions as well as the surface area in contact

with the flowing water.

Laboratory experiments, Neretnieks et al. (1982), and Allard et al. (1978), and a preparatory field experiment, Abel in et al. (1982), have shown two mechanisms that are of great importance for the magnitude of the retardation of migrating radionuclides:

2

1. Diffusion into the rock matrix adjacent to the fracture and sorp

tion on the inner surfaces.

2. Channelling within a fracture i.e. only certain part of the

fracture conducts water.

The first mechanism considerably enhances the bedrock's capacity to

retard the radionuclides. The second mechanism counteracts the first

by reducing the contact surface between the flowing water and the bed

rock. It also may give rise to 11 fasv• channels.

3

2 PURPOSE

The main purpose of this investigation was to investigate if it is possible to extend results on sorption and retardation of radionuclides in granitic rock, obtained from laboratory experiments, to a real environment with migration distances up to 10 m.

Further it is of interest to try to determine the extent of channe 1-

1 ing within fractures. Channelling would reduce the surface area in contact with the flowing water and thereby affect the retardation of

the radionuclides.

The experience gained from these 2-dimensional i.e. single fracture experiments should be used when designing and running an experiment

over a large volume of rock to study 3-dimensional dispersion and

channelling.

The objectives may be summarized as follows:

o To obtain a basis for comparing laboratory data on sorption with observations in a real environment

o To observe the movement of nonsorbing and sorbing tracers under controlled and well-defined conditions in a real environment

o To interpret the movement of the tracers in such a way that the results become useful for the prediction of radionuclide migration

o To develop good techniques for the sampling of small volumes of water and sampling of fracture surfaces with sorbed tracers

o To gather experience with stable tracers before using radioactive tracers.

4

3 EXPERIMENTAL DESIGN

3.1 Genera 1

The design of the experiment was based on the idea that reasonably

well defined individual fractures can be located and that tracers can

be introduced into the natural water flow within a single fracture

without a large disturbance of the flow field.

The experiment was run in naturally fractured granitic rock at a

similar depth as an underground repository.

Figure 3.1 Schematic view of

tracer injection

Tracers have been injected into a

single fracture which has a 11 natural 11 water flow towards the

drifte Almost all water coming

out of the fracture at the face of the drift was collected.

Figure 3.1 shows a schematic view

of the fracture with one of the

injection holes and several

s amp l in g ho l e s.

Migration distances of 5 and 10 m

have been used, which is more

than one order of magnitude

larger than the distances that

have been used in the laboratory experiments.

Conservative (nonsorbing) tracers have been used to characterize the

water flow within the fracture.

The results from the runs with the nonsorbing tracers and data on

sorption and porosity obtained in the laboratory have been used to

predict the breakthrough curve for a sorbing tracer. The predicted

breakthrough curve would later be compared with the experimentally ob

tained breakthrough curve.

5

It was predicted, based on results from the preparatory investigation

and 1 abor atory data, that only Sr wou 1 d have a chance to reach the sampling points during the experiment. The sorbing tracers would be

strongly sorbed in the immediate vicinity of the injection hole. To see how far out from the injection point these tracers had reached,

parts of the fracture surface around the inject ion point have been

excavated and an a lysed for sorbing tracers both on the fracture sur

face and at up to 5 mm distance into the rock matrix.

As no radioactive tracers could be used, stable tracers with the same

chemical behaviour as the important radionuclides have been used.

The main points for the layout of the experiment are summarized below:

o A natural fracture in granitic rock at a similar depth to the

depth of a potential repository has been used.

o The fracture has a 11 natural 11 water flow because the drift is

about 360 m below the water table.

b The additional water flow due to the tracer injection has been

small compared to the natural water flow.

o Almost all water emerging from the fracture has been collected

and kept under anoxic conditions.

o Conservative (nonsorbing) as well as sorbing tracers have been

used.

o No radioactive tracers could be used.

o After the tracer runs a considerable part of the fracture has

been excavated and the surface analysed to determine the migra

tion distances and penetration depth of the sorbing tracers.

6

The experimental design and instrumentation is described in more

detail in a separate report Abelin and Gidlund (1985).

3.2 The preparatory investigation

Before starting the main experiment a preparatory investigation was made. This was done to test the ide a and to develop equipment to be used in the main investigation. In this experiment only nonsorbing tracers were used. One of the results was that there seemed to be channelling within a single fracture. With this in mind the main experiment was modified. Instead of one injection point several points were used. This was done to reduce the possibility that all of the injection points would be located in nonconducting parts of the fracture.

Results from the preparatory investigation is given in Abelin et al. (1982).

3.3 The main investigation

The main investigation consists of five major parts, namely:

o Location and preparation of the test site.

o Test of connection between injection points and sampling holes.

o Tracer injection and water collection.

o Excavation and analysis of fracture surface.

o Interpretation of results.

Only the four later parts will be treated in this report.

7

Figure 3.2 shows the actual layout of the test site with two fractures and five injection holes intersecting the fracture planes. Tracers were injected into fracture 2 only.

@Sampling holes

Figure 3.2 Schematic view of test site.

Test of connection

To locate the connections between injection holes and sampling holes pressure pulse tests were performed. The aim of the pressure pulse tests was to give a qualitative answer if there was sufficiently good

connection for tracer injection purposes. The aim was not to quantify the hydraulic properties of the fracture in detail although the data obtained also were used to determine some additional hydraulic properties. The results of the pressure pulse tests are given in chapter 6 "RESULTS 11

•

Tracer injection

The four different groups of tracers that were originally intended for use in the main investigation were:

o Conservative (nonsorbing) tracers

o Sorbing tracers (analogs for radionuclides)

8

o High molecular weight solutes

o Particles of colloidal size.

Different particles were tested in the 1 aboratory for use as tracers but no suitable particles were found. A presentation tested nonsorbing tracers is given in Abelin and Gidlund (1985).

The following tracers and injection concentrations have been used:

Nonsorbing: Albumin Brom Thymol Elbenyl

Eosin Iodide Uranine

Sorbing: Cs I

Sr II

Eu III

Nd I I I

Th IV u IV and

( 1 arge molecule) Blue (BTB)

(dye)

(dye)

(anion) (dye)

(Oxidation state)

VI

Injection concentration

ppm

100 150

40

ll 93

80 23, 31

60

30

0.02

Oo2

< 0.001

3

The sorbing tracers were continuously injected at one injection

point, H2, during seven months (Sr 5 1/2 months, U 3 months). The nonsorbing tracer pulses injected at the same point as the injection of the sorbing tracers was done by using a mixture of the nonsorbing and

the sorbing tracers. In this way the nonsorbing tracers could be superimposed upon the sorbing tracers without disturbing the flow rates or breaking the continuous injection of the sorbing tracers. At the injection points where only nonsorbing tracers were injected, groundwater was continuously injected between tracer pulses to maintain the same flows everywhere throughout the experiment.

9

The injections were done by using a small overpressure about 10%

above the natural pressure at the injection point. Injection with such

an overpressure close to the natural pressure caused problems with the

i n j e c t i on f 1 ow rates . S m a 11 v a r i at i on s i n i n j e ct i on pres sure caused

large variations in the injection flow rates.

Excavation and analysis of fracture surface

Of the sorbing tracers only Sr was predicted to reach the sampling points within the time of the experiment, the rest of the tracers

wou 1 d be sorbed in the rock surrounding the injection point. To make

it possible to analyse surface concentration and penetration depth of

the sorbing tracers, part of the fracture around the inject ion point

has been excavated.

Interpretation of results

The breakthrough curves from the injections of the conservative tracers have been used to determine the flow parameters for the actual

fracture. The flow parameters combined with laboratory results on Ko and De and e:p have been used to predict the breakthrough curve for Sr.

10

4 INSTRUMENTATION AND SITE PREPARATION

A detailed description of instrumentation and site preparation is given in Abelin and Gidlund (1985).

4.1 Water flow monitoring

To monitor the flow rates, before drilling of any sampling holes, it was decided that fractures of interest should be covered, with plastic

sheets. These were glued to the face of the drift. The plastic sheets

also prevented evaporation due to ventilation.

The method of covering fractures to monitor the water flow rates worked well. There was some leakage between the plastic sheets covering the same fracture which reduced the accuracy of determining the variation of water flow rates from different parts of the fracture.

4.2 Site preparation

Injection holes

H5 0

H4o ~3

H1 0

0

H2

G2 0

Figure 4.1 Location of injection and some collecting holes in

A total of 5 inJection holes were used. They were core dr i 11 ed with a diameter of 76 mm. In figure 4.1 the location of the intersections of the injection holes with the extrapolated plane of fracture 2 is given. When the directions of the injection holes were decided it was not known which one of the fractures 1 and 2

was going to be used for the mi gration experiment. The injection holes were located in such a way that three of them were 0.5 m apart at

the intersection of fracture 2. This was done to see how the fracture varied over a short distance. The fourth hole was placed about 4.5

metres from the other three. These four holes have an average distance

11

from the intersection of the fracture to the drift of 5 m. The fifth injection hole was placed at a distance of 10m from the drift.

While drilling hole G2, 1.2 m of the core was lost. Although TVinspection did not show any anomalies, this hole was discarded and

plugged with several inflatable packers.

Sampling holes

A total of 31 sampling holes were drilled, 13 in fracture 1 and 15 in fracture 2. Three sampling holes were drilled outside the actual fractures at places where moisture was seen at the face of the drift. The location of the sampling holes are given in appendix 2.

4.3 Location of injection points

The combinea results from three different methods:

o core logging

o TV-logging

o pressure pulse tests

were used to decide which fracture to use as well as to locate the depth in the injection holes where the best connection with sampling holes 2-8 and 1-6 occurred. The two sampling holes chosen as observation points were those with the highest water flow, 1-6 in fracture 1 and 2-8 in fracture 2.

Table 4.1 gives the depths finally chosen for injection points in the various injection holes. The geometric consideration was based on the locations of the fractures found from pressure pulse tests and not on the geometry of the fracture 2 at the face of the drift.

12

Table 4.1: Location of injection points in injection holes

Injection hole depth (m) Method of loction

H1 16.27 pressure response in H2 H2 15.77 pressure response in

sampling hole S2-8 H3 15.19 pressure response in H2 H4 14.82 geometric consideration H5 13.61 geometric consideration

4.4 Pressure pulse test

The pressure pulse test equipment consists of two major parts:

o Data acquisition system o Injection system

The system monitored the water loss rate as well as the pressure responses in the injection and sampling holes. The data were stored on tape and 1 ater processed by HP85 to give p 1 ots of pressure response

and water loss rate versus time. The built-in printer in the HP85 was used as a real-time recorder for the pressure responses.

4.5 Equipment, injection of tracers

The overall requirements for the equipment were that it should be poss i b 1 e to do a step introduction of tracers into the fracture and

that it should also be possible to overlay a conservative (non-sorbing) tracer pulse on the sorbing tracer injection as well as to take out small volume samples from the injection compartment.

13

A detailed description of the equipment and procedures is given in Abelin and Gidlund (1985). Below only an outline of the most important parts is shown.

A schematic drawing of the injection equipment is shown in figure 4.2.

-o---c:J-INJECTION -o---o- FILLING

Figure 4.2 Main parts of equipment outside injection hole

Figure 4.3 Mechanical straddle packer system

The packer system was designed to be stationary in the injection hole with no need of frequent movement.

14

1. INLET VALVE N2

2. OUTLET VALVE TRACER SAMPLE 3. CHECK VALVE 4. INLET TRACER SOLUTION

TRANSPORT

Figure 4.4 Injection compartment

4.6 Water collection

The main criteria for the water sampling and collection equipment were that sampling and collection could be done under anoxic conditions and that as much as possible of the water should be collected.

4.7 Excavation of the fracture

After the injection of tracers was stopped, part of the fracture surrounding the injection point, where the sorbing tracers were injected, was excavated. The excavation was done by core-drilling in the plane of the fracture with a drill diameter of 0.2 m. A total of 16 main cores were taken out, with an average length of nearly 5 m.

15

Figure 4.5 Excavation of main cores

/ FRACTURE PLANE

INJECTION HOLE H2

Those parts of the cores which were of interest were taken to the

laboratory for further examination. Small sample cores were drilled

out perpendicular to the fracture surface. The diameter of the

sampling core was 23 mm and the length varied between 20-50 mm.

Using a grinding machine with a diamond coated metal ribbon, 0.2 mm

sections of the sample cores were ground off starting trom the fissure

surface. The depths reached in this way varied between 0.2 mm where

only 11 Surface 11 samples were taken, up to 5 mm where depth profiles

were made. These samples were analysed for their content of sorbing

tracers. In this way it was possible to determine the 11 Surface 11 con

centration and penetration depth for the sorbing tracers.

16

5 MODELLING

5.1 Modelling of flow and pressure pulse tests

5.1.1 Introduction

A series of tests were performed to locate a fracture in the main

injection hole H2 which has a good connection to collection holes in

the drift and to the other injection holes. This was done by sealing

off the innermost part of the hole by a packer and pressurizing the

sealed off portion to a constant pressure. The flowrate to this

portion was monitored and the pressure at one or more of the

collection holes in the wall of the drift was monitored as well as in several other injection holes. All holes were water filled and sealed

off with packers. After each test the packer in H2 was moved out a

certain distance which was determined by the location of visible

fractures on the core from the injection hole H2 and from TV

inspection of the hole. The procedure is described by Abelin and

Gidlund (1985).

The location of the injection hole H2 and the collection holes are

given in appendix 2. The pressure and flow responses are exampl ified

in figure 5.1. Other holes were also used as injection holes and then

the responses were measured in the holes surrounding this as well as

in the collection holes.

[bar] 5

4.6 4.2 3.8

Depth --12.09m ---15.74m -----15.85

3.4 -·-·-17.89m '/ 3 '/

~ 2.6 ~

7 / ' 2.2 -'/" ,.,.....-""' ,, __ _ =-= =----=-~=--=-=--- _... 1.8

17

1.4 -··-~·-··-··-··-··-··-··-··-··-

1 +-J\.,........-.-....,....,..,----.--r-T"T">,.,.,.,.,---.--r-....-rn,.,.,-..-r--r~ [ s] 1 100 1000 10000 100000

[ml/h] 4000 3800 " " 3200 " 2800 " " 2400 " " 2000 .........

........

1800 ........ ,

1200 800 ____ /\ 400 ------

0 [s] 1 100 1000 10000 100000

Figure 5.1 Example of water loss rates and pressure responses in

sampling hole 2-8.

5.1.2 Theory

The hydraulic head h will change in time and space when the disturb

ance is introduced. This is described by the following expression

which describes the conditions in an infinite fracture for radial symmetry.

(5.1.1)

The initial and boundary conditions for an initially constant hydrau

lic head distribution are

t < 0 t ) 0

t )

r > a

r = a h = 0

h = h0

h = 0

(5.1.2a)

(5.1.2b) (5.1.2c)

18

Because of the presence of the drift the conditions 2a and 2c are not entirely fulfilled. There is already a pressure distribution in the fissure due to flow into the drift. This is accounted for by defining

h as head above the stationary pressure. If the radius of influence of the injection hole is small compared to the distance to the drift and the pressure step is large the above conditions apply approximately.

The flow situation for the drift can be considered to be stationary on the time sea 1 e of the pressure step experiment used. Thus h and h0

are taken to be hydraulic heads re 1 at i ve to the head in the fissure before the experiment starts.

The solution is (Carslaw and Jaeger 1959, p. 335)

h

where

and

T t 't = s ~

0

p = r/r 0

(5.1.3)

J0 (u) and Y0 (u) are Bessel functions of zero order of the first and second kind respectively.

Hantusch (1964) also gives extensive tabular values of the integral in equation (5.1.3). A plot of h/h 0 vs. 't/(p-1) 2 is given in figure 5.2 for different p.

Equation (5.1.3.) and figure 5.2 can be used to evaluate T/S from the head versus time curve.

19

The flowrate into the fissure can be obtained from

dh Q = -T 2 n: r o Trf r=r o

dh where drjr=ro is obtained from equation (5.1.3).

The result is (Carslaw and Jaeger, 1959, p. 336)

where

o(h/h0

)

o(r/ro),r=ro = 4 j e-'t'u 2 du

0 u (J~ (u) + Y~ (u)) - 1t2

o(h/h0

)

o(r/r Jlr=r is plotted in figure 5.3. 0 0

(5.1.4)

(5.1.5)

(5.1.6)

20

1 h/h0

Erfc ( e -1 )or lim r/r ~1

2\1-r 0

0.5

~

0 10-1

/ v ~ ~ ~

) .. ...; ~ ~

;,.

, ~ ,

I~" .... /~ ... ~~

V' , ~ ~

~ ~ ~ ~ ....,. ~

.,. ~ ~ ~ ,...

10

~ ~ ~

..... ~ ~-~ r/r0 · :3

,.,., ....... ~ """"' ~

~ ~ 10 --~ ~ ~ .. ~ ~ II"'"" ~ """" ..,..,. ~ ~ ~

~

Figure 5.2 h/h0

vs. ~/(p-1) 2

" ........ + 0.0

.........

'~ ............. .............. ........ -~

--~

,..,

----

- 1.0 +0.0 + 1.0 + 2.0 +3.0 + 4.0

Figure 5.3 o(h/h

0)

log ~Flr:Tjr=r vs. log ~ 0 0

~

-~ ...... ~

~

~ ~

103 104

( -r/((>-1)2)

-+ 5.0 + 6.0

log ( -z )

21

5.2 Modelling of tracer movement

5.2.1 Introduction

When r ad i onuc 1 ides are carried by water f 1 owing through a porous or

fractured medium, they are influenced by several mechanisms:

o Molecular diffusion in the liquid

o Velocity variations in the fluid within the medium (mechanical

dispersion)

o Velocity variations between channels in a porous or fractured

medium (channelling)

o Diffusion into the stagnant water in the porous solid (matrix

diffusion)

o Chemical or physical interactions (sorption, precipitation)

Molecular diffusion occurs when there is a variation of concentration

in the liquid phase. The overall dispersion will be more influenced by

the molecular diffusion at low flow rates. In most cases of interest

the mechanical dispersion dominates over molecular diffusion in the

flowing 1 iquid. In flow through fractured media where water-filled

microfractures exist in the solid matrix, diffusion into these micro

fractures will also occur. The stagnant water volumes in the matrix

may be much 1 arger than the flowing water vo 1 ume and can act as a

strong retention magazine for the nuclides.

Mechanical dispersion is caused by local variations in the flow velocity both in magnitude and direction. If the velocity variations are of

random nature and frequent mixing occurs, then mechanical dispersion will behave very similarly to molecular diffusion but with a larger

magnitude. When mixing is scarce between channels the process is not

similar to molecular diffusion.

22

Hydrodynamic dispersion includes the effects of both mechanical dispersion and molecular diffusion. Bear (1969) gives a comprehensive

review of hydrodynamic dispersion theories. Mathematically, it is

treated in the same way as molecular diffusion.

Channelling dispersion occurs when water flows through non-interconnected or seldom connected channels with different water velocities. Due to the velocity difference, dissolved species will be transported different distances over a given time. This spreading mechanism has been described by Neretnieks (1983).

Sorption on the fracture surface and sorption within the matrix are examples of interaction with the rock matrix.

Effects on nuclide migration by different mechanisms

The following mechanisms were deemed to be of interest, namely:

1. Advection

2. Hydrodynamic dispersion

3. Diffusion into the rock matrix

4. Channelling within a single fracture

5. Sorption on the fracture surface

6. Sorption within the rock matrix of species which diffuse into the matrix.

A large hydrodynamic dispersion has the effect that some of the radionuclides would emerge to the biosphere at an earlier time than the

average but on the other hand they would be more diluted. The earlier arrival will give less time for decay.

Diffusion into the rock matrix surrounding the water-bearing fractures wi 11 withdraw the species from the flowing water and wi 11 delay the arrival of the radionuclides to the biosphere. Diffusion into the rock

23

matrix gives access to very 1 arge surf aces within the rock on which

the radionuclides can sorb.

If the channels within a fracture plane have very different water velocities, the fast channels will permit less retention time and thus

1 ess decay of the rad i onuc 1 ides. There wi 11 a 1 so be 1 ess of the fr acture surface which is in contact with the mobile water and thus less

surface with which to interact by sorption and from which to diffuse

into the micropores of the rock matrix. Retardation may thus become

considerably smaller than if all the fracture surface were equally

accessible to the water.

The sorption of the radionucl ides on the fracture surface is one of

the mechanisms which considerably retards the migration of the nuclides. The magnitude of this retardation mechanism is proportional

to the surface in contact with the flowing water and could be considerably decreased due to channelling within the fractures.

Channelling is very little studied, experimentally as well as

theoretically. Projections made, (Neretnieks 1983), indicate that it

can have a very strong influence on the migration of radionuclides.

The experiments were designed so that the above mentioned mechanisms could be studied.

The modelling work consisted of the following parts, namely:

o Adaption of models to describe the physical situation in the

experiment.

o Fitting the experimental data from the runs with the conserva

tive tracers to obtain the hydraulic parameters of the fracture (fracture width, dispersion).

24

o Prediction of a breakthrough curve for a sorbing tracer using the results from the nonsorbing tracer runs and laboratory data

for Kd.

o Prediction of sorbing tracer concentration on the surface of the fracture along the flow path.

o Prediction of concentration profiles (sorbing tracers) within the rock matrix.

When fitting the experimental data to the models, a nonlinear least square technique was used.

Models used

General

For a one dimensional flow in a channel, assuming advection and dispersion, the variation with time in the concentration of a tracer

in the fluid in the fracture can be described by:

(5.2.1)

The term f(Cf,,,) accounts for reactions of the tracer with the fissure surface and/or rock matrix.

Two different models for the reaction have been tested, namely:

o Advection-dispersion surface reaction model.

o Advection-dispersion-matrix diffusion model.

The latter model actually also contains the mechanism of surface sorption so the difference between the models is that of matrix diffusion and sorption on the inner surfaces of the matrix.

25

The concentration at the outlet, for the advection-dispersion model, can be written in a condensed form as:

C(t) = C Pf f (Pe,t ,R ,t) o w a (5.2.2)

C0 is the injection concentration, Pf accounts for dilution

effects, Pe is the Peclet number, t 0 the mean residence time, Ra

is the surface retardation factor, defined below in equation (5.2.8). When fitting the data from the runs with the con serv at i ve tracers

(Ra=l), and values for the parameters Pf, tw and Pe will be obtai ned.

The corresponding out 1 et concentration for the advect i on-dispersion

mat r i x d i f f us i on mode 1 i s :

C(t) = C Pf f(Pe,t ,R ,A,t) o w a (5.2.3)

The A parameter accounts for the interaction with the solid matrix and

includes data on matrix diffusion and sorption within the matrix. The

fitting of experimental data to this model was done in two ways. It

was either a three parameter fit giving values of Pe, tw and Ra

where A is calculated from laboratory data or a four parameter fit

where also the value of A was determined by the fitting procedure.

The applicability of the models and the various boundary conditions as

well as possible errors introduced in using different boundary condi

tions is discussed below, section 7.7.

Some definitions used

In the case of a surface reaction equation (5.2.1) can be written:

ocf 2 oC s ocf o2c -+--+U --0 __ f=O ot & ot f ox L ox 2 (5.2.4)

Assuming an instantaneous equilibrium and linear relation between the

concentrations of tracer in the fluid and on the solid surface, the

surface concentration can be written:

26

C = K C s a f

(5.2.5)

where Cf is the concentration in the fluid and thus:

(5.2.6)

Introducing (5.2.6) into (5.2.4) equation (5.2.7) is obtained

(5.2.7)

where Ra is the surface retardation factor, defined by:

R = 1 + £ K a & a (5.2.8)

If there is sorption within the rock matrix a volume retardation factor for the movement into the matrix is defined by:

(5.2.9)

I

where Kd is the volume equilibrium constant between the tracer con-centrations in the fluid and the solid. Also here a linear relation is used.

C = K1 C m d p (5.2.10)

I

In this case Kd is based on the mass of the solid proper.

The definition of the volume equilibrium constant is sometimes based on the mass of the microfissured solid and includes the nuclide which is in the water in the microfissures as well as that in the solid

(5.2.11)

27

and the volume retardation factor may then also be written as

(5.2.12)

I

For a conservative tracer Kd is 0 but Kdpp = EP (eq. 5.2.11) and the porous rock matrix still has a capability to withdraw nonsorbing tracers from the fracture fluid, because the pore water will

equilibrate with the fissure water, Cf = Cp at equilibrium.

With a large water volume in the pores, compared to the volume of flowing water in the fissure, this effect may be considerable.

5.2.2 The advection-dispersion model

The advection-dispersion surface sorption model has been used to test if it is possible to get a good fit between experimental data and a

model that does not take into account diffusion into the rock matrix.

The interaction between the tracer and the rock matrix is limited to sorption on the fracture surface. The following mechanisms are

included in the model, namely:

o Advective transport along a channel in the fissure.

o Hydrodynamic dispersion in the flow direction.

o Sorption onto the surface of the fracture.

The governing equation is given by equation (5.2.7).

This equation was analytically solved by Lapidus and Amundsen (1952) using the following initial and boundary conditions, namely:

28

Cf(x,O) = 0 (5.2.13 a)

Cf(O,t) = c 0

(5.2.13 b)

cf (co, t) = 0 (5.2.13 c)

The solution is

C Pe0·5(1-t ) Pe0· 5{1+tR) Cf = 0 [erfc R + ePe erfc ]

~ 2 t 0.5 2 t 0.5 R R

(5.2.14) where

tR = t/t0

(5.2.15)

Pe = Uf x/OL (5.2.16)

(5.2.17)

5.2.3 The advection-dispersion-matrix diffusion model

In this model the mechanisms of matrix diffusion and sorption within the matrix are introduced in addition to the instantaneous surface sorption in equation (5.2.7).

The system can be described by:

a2cf 2 aCP o--0- I =0 L ox 2 e & az z =O

0 ( X ( oo (5.2.18)

Assuming a linear equilibrilJTl isotherm for the surface sorption and introducing the surface retardation coefficient Ra, defined in equation (5.2.8), equation (5.2.18) transforms to:

29

oCf oL o2Cf uf oCf 2 De oC

lit- Ra 1lx2 + Ra-;--- 6 Ra a!"lz=O= 0 (5.2.20)

0 ( X ( 00

The differential equation for the porous rock matrix is:

(5.2.21)

Assuming a linear sorption equilibrium within the porous rock, and introducing Rd defined in equation 5.2.12, equation 5.2.21 becomes

(5.2.22)

The two coupled equations (5.2.20) and (5.2.22) were solved analytically by Tang et al. (1981) including radioactive decay for the

following initial and boundary conditions:

For the fluid

in the fissures

For the fluid

in the matrix

Cf(O,t) = C0

Cf(oo,t) = 0

Cf(x,O) = 0

Cp(O,x,t) = Cf(x,t)

C (oo,x, t) = 0 p

Cp(z,x,O) = 0

(5.2.23a)

(5.2.23b)

(5.2.23c)

(5.2.24a)

(5.2.24b)

(5.2.24c)

where C0 is the concentration at the inlet of the fracture.

30

The concentration of a nonradioactive tracer, in the fracture fluid,

at a given time and distance from the source is

where

erfc

X t=R-=Rt

0 a uf a w

(5.2.25)

(5.2.26)

(5.2.27)

(5.2.28)

(5.2.29)

This model has previously been used to evaluate tracer tests in real

fissures in laboratory experiments (Moreno et al. 1984) and a field

experiment at the Finnsjon site (Moreno et al. 1983).

The solution for the concentration of tracers, in the pore fluid, in

the matrix, at a distance z from the surface of the fracture is:

where

erfc

Pe t B __ o....,..+~

( 8 A c: 2 2

I Pet t - 0

4 ~2

B =It e

31

) d~ (5.2.30)

(5.2.31)

The integrals in equation (5.2.25) and (5.2.30) have no analytical

solution and are evaluated numerically. For further information see

appendix 3 where also the preparation of the experimental data before

modelling is described.

These solutions are for a step injection of tracers. Because the model

is linear these solutions can be used for a pulse injection by con

sidering the pulse formed by one step up part and one step down part

delayed in time by 8t. The pulse injections were performed with the

nonsorbing tracers.

The sorbing tracers were continuously injected from start of the

experiment. Due to the time delay, between the end of injection and

the excavation of the first main core, the fracture was subjected to a short flushing with water without tracers. During this period some

leaching has taken place. This leaching has also been treated as a step down change in concentration when modelling the concentration

profiles within the rock matrix.

The numerical solution of the advection-dispersion-matrix diffusion model

The boundary condition (equation 5.2.23a) which sets the concentration

at the inlet of the fracture equal to a constant con cent at ion C0 is

probably not a correct description of the physical situation. This is

32

especially the case when the dispersion is modelled by a hydrodynamic

dispersion with a constant dispersivity. In this case a boundary condition with a constant rate of injection of tracer may be a better

description. The boundary condition for this case becomes

I

(5.2.23a)

where Uinj is the average injection velocity over the breadth of the

channe 1.

To test the differences between these two boundary conditions the latter was also used in model calculations to predict the movement of

the sorbing tracers. A numeric a 1 technique was used to so 1 ve the

equations.

A computer program called TRUMP was used to solve the equations. It is

a program that solves a general nonlinear parabolic partial

differential equation describing flow in various kinds of potential

fields. One, two or three dimensions are considered in geometrical

configurations having simple or complex shapes and structures.

A set of simultaneous partial differential transport equations with the four independent variables of spatial coordinates and time can be

solved. For further information on the TRUMP program see Edwards

(1969).

5.2.4 Channelling model

The model is based on the assumption that all channels conduct the

flow from inlet to outlet without mixing underway. At the outlet,

however, the fluid from all channels is instantaneously mixed. We

assume that the channels can be uniquely described by their openings

as regards the flow rate and concentration response.

For the case with a discrete distribution F(oi) of channel openings

& i the eff 1 uent con cent ration in each ch anne 1 is denoted by

C(t,oi). The flow in each channel is Q{oi). Both C(t,oi) and

33

Q(oi) are assumed to be functions totally defined for every class of channel opening Oi· The mixed effluent from all channels has the concentration:

N E F(oi) Q(oi) C(oit)

c ( t) - _i _=1-,-,--__ -----~- N

E F(o.) Q(o.) . 1 1 1 1=

( 5. 2. 32 a)

For continuous distribution of channel openings f(o) we have:

CD

J f(o) Q(o) c(o,t) do C(t) __ o __ c;--

J f(o) Q(o) do 0

(5.2.32b)

A flow system with channelling will spread a tracer pulse along its pathways and the pulse will also be spread at the observation (mixing point), even if there is no spreading in the individual channels.

The concentration response C(o,t) in equation (5.2.32b) may be obtained by any of the previous or other models which describe transport in a single fracture or channel.

Figure 5.4 shows the response of a stratified system to a Dirac pulse at the inlet. The channel widths in this case were taken to be lognormally distributed and the cubic law for flowrate

3 Q = const1 • 6

was assumed to apply. The velocity then is

(5.2.33)

(5.2.34)

34

0 1 2 3 4 5 t/to

Figure 5.4 Concentration at the outlet of a medium with parallel fissures which has been injected with a tracer pulse.

For distribution F(oi) or f(o) which are described entirely by a mean ~1 and variance a~ the mean transit time f can be determined from the first moment. For a Dirac pulse at the inlet

co

f C(t) t dt £ = _o ___ _

co (5.2.35)

J c (t) dt 0 0

From the second moment the variance a~ can be determined

co

J c ( t ) ( t - t) 2 dt 0 CXI

J c (t) dt 0 0

(5.2.36)

From the latter the equivalent of the dispersion coefficient for an experiment can be determined.

(5.2.37)

35

From (5.2.35) and (5.2.36) the following simple expression for the

variance is obtained

(~t)2 = e4(.tn 10 cr.R/ _ 1 t

(5.2.38)

where o1 is the standard deviation in the lognormal distribution. From equation (5.2.38) it is seen that (ot/t) 2 is a constant for a

given o1 . In fact it has been shown that for an arbitrary distribution - f(o) -this applies (Neretnieks 1983).

From equation (5.2.37) is found that

DL = const • L (5.2.39)

It may be concluded from this, that if there is pure channeling in a flow region then an apparent hydrodynamic dispersion coefficient will increase with distance between injection and observation (mixing) points. Equations (5.2.37) and (5.2.38) give a direct and simple

relation between DL and o1 .

36

RESULTS

6.1 Pressure pulse testing

The pressure response curves h/h0 vs t are given in appendix 4 together with the flow response curves Q vs t. These curves have been matched with the theoretical curves in figures 5.2 and 5.3. The evaluated transmissivities and storativities are summarized in appendix 5. The location of the injection points and measurement points are

shown in figure 6.1. The figures at the hole notation refer to the distance into the holes.

H1 0

H5 0

H4o ~3 0

H2

G2 0

In hole H2 the transmissivities of the fracture obtained in the different tests are consistently

between 2.8-6.5•10- 10 m2/s. The storativities are between 3.6•10- 8

and 7.5•10- 8 • The hydraulic diffusivities T/S between hole H2 and other points range from

1.3•10- 4 6.1•10- 2 with most values around 3-5•10- 3 • These results were obtained by between ho 1 e measurements and are in the same range as the T/S obtained from water flow measurements.

Thus when injection is made in H2 at 15.77 m there is good connection to all other points including the collection points at the drift wall

S2-8, S2-6.

When other holes are pressurized the responses are very weak if at all measurable. The hydraulic transmissivities in holes H1, H3, H4 and H5 are more than zn order of magnitude less than in H2.

37

The transmi ssivit ies obtained by the above method can be compared to

those obtained from measurements of the mean residence time for the

natural flow to the drift, and the "steady state" flowrate. The

undisturbed flow residence time was obtained from tracer tests in the

fissure (Abelin et al. 1984). The result is: T = 8.4•10- 10 m2/s. In

another monitoring hole 1.4 m further away (52-6) T = 1.1•10- 10 m2/s.

This is well within the range obtained by the hydraulic tests. T is

defined as the product of the hydraulic conductivity and the thickness

of the aquifer.

6.2 Water flow monitoring

The water flow rates were monitored at four different occasions, name

ly:

o Before any drilling took place

o After the water collection holes were drilled but before the

drilling of the injection holes.

o During the period just after the pressure p~l se tests when the

preinjection of groundwater was performed.

o Near the end of the tracer runs.

The water co 11 ect ion started when the fractures were covered with

plastic film. These measurements could just give qualitative results

due to leakage but showed that only parts of the fractures conducted

water.

After the water collection holes (sampling holes) were drilled and

before the dr i 11 i ng of the injection holes the water flow from the

sampling holes was monitored.

Just after the pressure pulse tests and during the preinjection of

groundwater, the outflow from some of the sampling holes was monitor

ed. These water flow rates were influenced by the water injected, but

38

it was only sampling hole 2-8 that had a significant rise in the water flow rate.

During the first part of the actual injection of tracers it was not possible to monitor the flow rates, but after the modification of the water collecting system, the water flow rates could be monitored.

The results from the monitoring before the drilling of the injection holes and the results at the end of the tracer runs are summarized in figure 6.2, where also the tracer flux from different sampling holes is presented. The values are averaged. There is no large difference between the flow rates monitored at the two occasions.

\ \

\

\ ',, IDEALIZED

''STREAM LINES •

' \

,.FRACTURE1• / I

/ FRACTU,RE 2

Figure 6.2 Water flow rates in fractures 1 and 2.

In fracture 1 there occurred a decrease in the water flow rates of 50 % or more during a time period of 130 hours after which the water flow rates went back to normal. Such a decrease was only noticed once during the monitoring period.

6.3 Conservative tracer runs

To summarize the results from the nonsorbing tracer runs:

When injecting Uranine at injection point H2, measurable amounts of tracers arrived in sampling holes 2-6* and 2-8. The response in 2-9 was just above the detection limit and in sampling hole 2-10 only traces of the nonsorbing tracer was found.

*) For the location of the sampling holes see appendix 2.

39

Eosin which was injected at injection point H3 was found in sampling holes 2-6 and 2-8.

At the 10 m distance, injection point H1, Elbenyl Brilliant Flavine was injected. Traces of Elbenyl were found in sampling holes 2-6 and 2-8. These curves could not be fitted by the models.

Table 6.1 shows all the different injections performed during the test period and their duration in time;

Table 6.1 Different tracer runs and their extension in time.

Injection Tracer hole

H1

H2

H3

H5

BTB Elbenyl

Iodide Glue

Urani ne Sorbing

Albumin Eosin Cr-EDTA

Dec Jan Feb Mar Apr May Jun Jul

(----------)

When looking at table 6.1 one can ask why most of the injections were performed at the end of the test period. The explanation to this is

that during the first injection of Eosin at injection point H3 it was noticed that it was impossible to keep the variations of the injection flow rate within acceptable levels. A new method of injection had to be developed. Having flow rates down to ml/h did not make the problem easier. Pumps with which it was possible to keep a constant injection flow rate independent of pressure were bought. Some of the new pumps

40

did not fulfil the specifications from the manufacturer so after a time they did not deliver any flow. At this point it was decided to go back to the old method of injection at those injection points where the pumps did not work.

There are no results from the injection of Cr-EDTA and Albumin, Cr-EDTA due to malfunction of injection equipment and Albumin due to unreliable analysis at low concentrations.

Injection point Hl is located at approximately 9.5 m from the sampling holes. The injection of Elbenyl Brilliant Flavine did give a response at sampling points 2-6. The response was just above detection limit and time for arrival was 1500 hours. The injection of BTB was superimposed on the injection of Elbenyl at injection point Hl when no Elbenyl at that time had arrived at the sampling holes. The time between start of injection of BTB and the end of the test period was to short for BTB to reach the sampling points. No transport parameters for this flow path could be determined.

The results from the other injections will be presented for one injection point at the time.

41

At injection point H2, which was located at an average distance of 4.5

m from the sampling holes in fracture 2, where both nonsorbing and sorbing tracers were injected. The nonsorbing tracer pulses were superimposed on the continuous injection of the sorbing tracers. The breakthrough curve obtained at sampling hole 2-6 for the two injections are shown in figures 6.4 and 6.6. Figures 6.5 and 6.7 show that breakthrough curves obtai ned at samp 1 i ng ho 1 e 2-8 for the two injections of Uranine. The injection flow rate at first injection is presented in figure 6.3. At the second injection, with a constant

injection flow rate of 2.6 ml/h, Iodide was mixed with Uranine so the response from two different tracers could be obtained simultaneously.

25

20

2 ' r-

\ ]

r-~

.............

~ 1- ~

~ r-

~ -----

Ql 15 .j.) 0 L

• 0 ;: c: 10 0

~ 0 (J ..., .5

5

-

100 200 300 400

Time from start of injection [h]

Figure 6.3 Injection flow rate for first injection of Uranine in H2. The histogram indicates the flow rates used in the fitting

of the tracer breakthrough curve.

42

.30 ~--------------------------------------------------------~

'0 u ......

.25

8 .20 c 0 ..., 0 L

~ .15 3 c 0 (J

~ ~ .10 0

& .05

,.,

:~":t~\ ~\ ...... . ':

<t

. -..._ ______ , __ o.oob~~~~~~~~~~~~~~~~~~~~~~~~~~~-=~.

0 500 1 000 1 500 2000 2500 3000

Tim~ from start of injection [hours]

Figure 6.4 Breakthrough curve sampling hole 2-6, first injection in H2 .

• 06

.05

'0 u ...... 8 .04 c 0

~ a L ...,

.03 c CJ 0 c 0 0

CJ >

.02 ..., a (j ~

• 01

o.oo 0

I

! i I

l .f

,If!\ j ~ i \ i I

500 1000 1500 2000 2500 3000 Time from start of injection [hours]

Figure 6.5 Breakthrough curve sampling hole 2-8, first injection in H2.

43

.lOr-----------------------------------------------------.

.08

~ 8

~'I-c 0 .06

~\ ~ D ,_ ..., c g B .04 Cl > ~ D -; 0:

.02

Tima from injaction Ohourel

Figure 6.6 Breakthrough curve sampling hole 2-6, second injection in H2 .

. OSr-----------------------------------------------------,

.04

~ c 0 .03 ~

b

I .02 Cl >

i -; 0:

• 01

0.00 0 200 ..00 600 800 1000

Till& fro11 1njaction thourel

Figure 6.7 Breakthrough curve sampling hole 2-8, second injection in H2.

44

Injection point H3 was located at an average distance of 4.5 m from

the sampling holes in fracture 2. At this injection point two injec

tions, of the nonsorbing tracer Eosin were performed. The injection

flow rate for the first injection is presented in figure 6.8. The

breakthrough curves obtained at sampling hole 2-6 from the two injec

tions are presented in figures 6.9 and 6.10. The breakthrough curve at

sampling hole 2-8 for the second injection is presented in figure

6.11. The injection flow rate for the second injection was constant

1.22 ml/h. The response in sampling hole 2-8 from the first injection

was just above detection limit so for the second injection the

concentration of Eosin was raised 4 times.

5~------------------------------------~

~ ..... :! Gl 3 "6 I.

t ::: c

2 0

:: u .!!, ,!;

200 400 600 BOO 1000 1200

Tinali from stort of injoaction [hourul

Figure 6.8 Injection flow rate first injection in H3 .

• OS

.04

a u ..... !::! r:

~ .03 0 L .. r: Ql u c 0 u .02

.··-·-·· .. ··~····._ ...... ·· Ql > ::; 0

C» a.: .01 .............. :

o.oo 0 300 600 900 1200 1500

Ti•11 frora &tort of injliction [hours)

Figure 6.9 Breakthrough curve in 2-6~ first injection in H3.

45

.OS ~---------------------------------------------------------.

.04

8 ....... 8 c 0 .03 :; a L

~ Cl 0 c 8 .02 Cl ..... > ....... :; a c; a:

.01 r-

0.00 0 300 600 900 1200 1500

Time from start of injection [hourel

Figure 6.10 Breakthrough curve in 2-6, second injection in H3

.0010 r-----------------------------------------------------------~

.0008

c 0 .0006

i <tJ c 3 c 0 0 .0004 Cl > :; a

(jj a:

.0002

....... · ,.:

.,..

.. ....... ""·.: '".

..

.. •

_: .. , ......... · , ·:

Time from start of injection [hours)

Figure 6.11 Breakthrough curve in 2-8, second injection in H3

46

It can be seen from the breakthrough curves in samp 1 i ng ho 1 e 2-6 that there seem to be three distinct flow paths from injection point H3 to samp 1 i ng ho 1 e 2-6. From the breakthrough curve from the first injection it is hard to see the channels due to the superimposed variation of the injection flow rate. At the second injection the injection flow rate was constant and the channeling could be clearly seen.

At injection point H4 the obtained injection flow rate was too low to get any appreciable amount of tracer into the fracture.

Table 6.1 shows that at the end of the tracer injections, glue was injected at injection point H2. This was done to make it possible to recognize the fracture used for the injection of the sorbing tracers when excavating the surroundings of injection point H2.

6.4 Calculation of fracture widths

The term fracture width or opening implies that this is a geometric property and that the fracture has a fairly constant opening. Our observations indicate that fractures are closed in some parts and are open in other parts. The opening thus may vary considerably over the "plane" of the fracture. Those parts of a fracture which carry water we call channels. They have at present unknown extension in the breadth direction as well as in the length direction, i.e. before they loose their identity by connecting with other channels. Any calculation of the fracture opening will thus include some assumptions on the other properties.

The flow to the drift could be well approximated by converging radial flow if the fracture had equal properties in the fracture plane. Thus this assumption is used in one set of calculations. As channelling is clearly observable, however, another set of calculations are performed based on the assumption that the flow is linear over the distance of the experiment.

47

In each of the above cases there remains to define what properties a fracture 11 0pening 11 has in this context. For a perfectly planar fracture with smooth walls and constant opening, only one figure should be needed to define all properties if the laws governing the properties are known. In fractures with varying openings and possibly with infilling material this is not possible any more.

One of the properties of interest is the average vo 1 ume of the fracture. This could be determined from measuring the flowrate over a width of the fissure and also the residence time of the water. We call this the mass balance fracture width.

Another property of interest is that equivalent fracture width which would permit a certain flowrate at a given pressure drop. This we call the cubic law fracture width.

A third equivalent fracture width is that which would give a certain water velocity for a given pressure drop. This we call the frictional loss fracture width. In the two latter cases pressure drop is assumed to be caused by friction between two parallel smooth plates for laminar flow.

The latter width differs from the two previous in that a 11fracture" could in principle consist of many thin parallel fractures to cause high pressure drop for a given veclocity, but the sum of the flowrates from them all is needed to get the total flowrate.

The significance of the various equivalent fracture widths will be further discussed in connection with the equations.

48

The data used for the calculations are given in table 6.2. The results from the calculations are presented in table 6.3. In the calculations it is assumed that all the flow passes the injection point.

Table 6.2 Data for calculation of fracture widths

** Sampling tw (h) Q (ml/h) 8H (m H20) r 1 (m) r 2 (m) hole

2-6 2-8 4* 5*

306 100 100 200

3.5 12.5 83

28

18

18

28 28

2.5 2.5 2.25 2.25

7

7

6

6

* Two sampling holes in the fracture used in the preliminary investigation.

** tw the mean water residence time is determined from the tracer tests see section 6.6.

The three different fracture widths are denoted by:

Mass balance &f

Cubic 1 aw &c

Frictional losses &1

49

6.4.1 Linear flow (L) assumption

When the mean residence time is known a fracture width can be

calculated by use of the mass balance. The volume of the fracture is:

(6.4.1)

Of is a real phys i ca 1 entity in the sense that it can be directly

measured or be derived from measured quantities and by the use of the

law of mass conservation. It is, however, an averaged quantity. From

equation (6.4.1), the fracture width as a function of mean residence

time, volumetric flow, flow path length, and assumed fracture breadth

can be calculated.

(6.4.2)

For laminar flow between two parallel plates the hydraulic conductiv

ity of the conduit is:

K = o2 _g__ pf i 12v

the water velocity in the fracture:

the mean residence time:

L t =w u

(6.4.3)

(6.4.4)

(6.4.5)

Equations (6.4.3) (6.4.4) and (6.4.5) give the fracture width as a

function of the mean residence time, pressure drop, fracture breadth

and length of flow path. Combining the equations gives

(6.4.6)

&1 = is not a real physical entity as it is based on the assumption of laminar flow pressure drop in a slit.

50

The cubic "law11 is based on the assumption that the pressure drop is caused by laminar flow in a slit with an opening o1 as in the previous case. It further assumes that the same opening also is equal to the mass balance width Of. Thus Of = o1 and is here denoted by oc. oc will be equal to the other o:s only in smooth parallel channels under laminar flow.

Combining equations (6.4.1, 3, 4 and 5) and using oc for both o1 and Of the cubic law fissure width is obtained

& = I Q L 12 v cl B 8h g (6.4.7)

It may be noted that only the flowrate, pressure drop and geometric entities are needed to determine oc. It thus does not include any information on residence time and thus does not directly or indirectly include the law of mass conservation.

6.4.2 Radial flow (r) assumptions

Again we assume that the fracture width is equal everywhere in the fracture or that an average meaningfully can be used.

When calculating the fracture width from the mass balance, the velocity along the flow path is not constant and the variation must be

accounted for. The velocity in the fracture at a radial distance r1 is:

(6.4.8)

tw is the residence time for travel between the radial distances r 2

and r1.

The volumetric flow is:

Q = (6.4.9)

51

The area of the crossection for flow in the fracture:

(6.4.10)

From equations (6.4.8, 9 and 10 a) fracture width ot"r is obtained

using assumed collection length B1

(6.4.11)

The hydraulic conductivity of a fracture with radial flow can be derived from the measured data by

r2 = 0.5 .R.n (-) (r2

2 - r12 )/t M1 r 1 w (6.4.12)

the equivalent fracture width for frictional loss becomes as before

6.tr = / Kpf 12 v/g ' (6.4.13)

the fracture width as a function of geometry, mean residence time, pressure drop and assumed collection length can be calculated.

For radial flow the cubic law has the form

(6.4.14)

52

Table 6.3. Fracture widths

1 i near radi a 1

Samp 1 ing K** 0fL o.RL 0cL 0fr 0lr hole pf (m/s*10""6) (m*10""6)

2-6 1.1 240 1.1 6.7 130 1.2 2-8 3.4 280 2.0 10 150 2.1 4* 1.5 2200 1.3 16 1200 1.4 5* 0.75 1500 0.9 11 820 0.96

* Two sampling holes used in the preliminary investigation. ** For radial flow.

0cr

5.5 8.5

13 9.1

A fracture with a fracture width corresponding to the one calculated from the pressure drop could not carry all the water entering the sampling holes. There have to be several of these fractures within the

fracture plane to obtain water flow rates equal to those monitored at

sampling holes 2-6 and 2-8.

53

6.5 Sorbing tracer runs

6.5.1 General

After the inject ion of tracers was ended, parts of the fracture were excavated, a total number of 16 main cores were taken out. The rock quality was very varying within a core and also between adjacent cores. There are variants from compact granite to gravel and fine sand. A schematic view of the main cores are found in Appendix 6 Fig. 1.

In the vicinity of the injection hole a near vertical fracture spread over 5 main cores was found. The excavated area of this fracture is

approximately 0.5 m2 • This fracture is referred to as fracture A. Figure 6.12 shows fracture A within 4 of the main cores.

Figure 6.12 Fracture A with the injection point H2 and some sample holes.

54

Sampling

To determine the pre-injection concentrations of the sorbing species, sample cores were taken from two different spots, namely:

• From the core obtained when drilling the injection hole H2. To get the pre-injection concentration of the tracers in the rock

adjacent to the fracture, five sample cores were taken.

• From the cores obtained from the drilling of the water collecting holes. Sixteen sample cores were taken to get more information on the pre-injection concentrations and a possibility to compare wet and dry parts of the fracture for "background.. content of tracers.

To determine the concentration of sorbing tracers after the injection sample cores were taken from the 16 main cores. A total number of 210 sample cores were drilled, the sampling frequency was highest in fracture A.

Preparation of samples and analyses

The sample cores were ground off in thin sections of approximately 0.2 mm starting from the surf ace of the fissure. Most sample cores were only analysed for their tracer content in the first section, referred to as the surface, more than 20 samples were analysed in depth, down to a depth of 5 mm, section by section.

Two different methods were used for the analyses of sorbing tracers (Sr, Cs, Eu, Nd, Th and U), namely:

• Atomic absorption analysis (AA) for Sr and Cs.

• Neutron activation analysis (NA) for Cs, Eu, Nd, Th and U.

The results from the two different methods of analysis of Cs give consistent results.

55

All results given in this report are total concentrations (including background).

There are no useful results for Nd or Th probably due to their low solubility in water, i.e. the injection concentration was too low, combined with the high background concentration in the rock.

A table summarizing the number of sample cores taken and the performed analyses is given in Appendix 7.

6.5.2 Sampling of pre-injection concentration (background)

The pre-injection concentration varied for all the tracers of interest but the variation was most pronounced for Sr. In Appendix 12 a histogram is found over all analyses performed of pre-injection concentrations.

Sample cores from the injection hole

In the core obtained when drilling the injection hole H2, at the depth of fracture No. 2, there was one fracture with a connecting fracture. A total of 5 sample cores, (194, 195, 196, 78 and 79) were taken from

these fractures. Two of these, which were beside each other, were analysed (AA) for variation in the concentration with the depth, giving different results for the content of Sr.

From the three other cores the surf aces were ana lysed for Sr and Cs. These results were all within the assumed 11 background" level. NA analysis was used for one of the cores to determine the concentration variation with depth of the tracer species. (The surface concentration was determined by AA analysis.) All tracer species show a variation in the concentration. Notable is that the concentrations decline slowly with the depth. All results are shown in Table 4.

Core no.

56

Table 6.4 Pre-injection concentration of the tracers in the rock adjacent to the fracture.

194 195 196 78 79

Mean depth Sr Cs Sr Cs Sr Cs Sr Cs Sr Cs Cs Eu Nd Th u mm

0-0.5 0.5-0.7 0.7-0.9

0.9-1&1 1.1-1.3

1.3-1.5 1.5-1.7

2.9-3.1

ppm ppm ppm ppm

35 5 35 10 35 10 65 5 40 5

25 10 7 0.68 42 29 104

25 15 20 10 7 0.59 35 32 90 25 10 30 15 6 0.53 30 28 69

20 10 30 15 5 0.47 24 27 55 20 10 15 10 4 0.50 19 21 32

20 10

20 10 9 0.31 12 13 23

Sample cores from water collecting holes

There was a large variation in the pre-injection surface concentration for Sr. Table 6.5 shows the pre-injection surface concentrations of

the tracers at some of the water collection holes and the measured water flow rates in those holes. Comparing dry and wet holes gives a

clear indication that the dry collection holes have a higher surface concentration than the wet ones but the results are ambiguous. A 11

resu 1 t s obtai ned from an a 1 ys is of the samp 1 e cores from the water collecting holes are given in Appendix 8 Table 6.4.

There are some indications that the background concentration is

different in areas where natural flow occurs from areas where there is no flow.

57

Table 6.5 Pre-injection surface concentration at some of the water collecting holes and the measured water flow rates.

Samp 1 ing Core no. Water flow Sr Cs Cs Eu Nd Th u hole ml/h ppm ppm

s 1-1 green 0 dry 55 0 prov 20 5

0 III 87.9 <0.35 <147 19 102

s 1-11 92 dry 140 20 s 2-3 193 dry 260 10

s 2-4 197 dry 190 10 198 55 10

s 2-7 176 dry 9 2.2 181 30 31 177 70 10

s 2-1 94 0.2 25 5

178 4 0.60 42 28 37

s 1-4 93 1.3 85 15 s 2-10 191 2.8 25 10

s 2-6 174* 3.0 7 2.9 173 41 94 175* 380 10

s 2-8 192 13.0 20 15

* Sample from very thick fracture alteration material.

6.5.3 Determination of sorbed tracer concentrations

Samples from the vicinity of the injection hole

Spots of the injected glue were found on three different fractures, namely:

58

• Fracture A, on both sides of the injection hole

• A horizontal fracture in main core no. 10, in level with the injec~

tion point.

• Fracture B, in the vicinity of the injection hole*.

* For the location of fracture B and the glue spots see Appendix 6 Figure 4.

This gave information on possible pathways for the injection flow. However, further sampling from fracture B, the fracture in main core no. 10 and the surrounding cores gave no pronounced level of tracer.

Surface analyses from fracture A

The AA analysis of Sr and Cs from the samples from fracture A indicates a flow from the injection hole out to the right, passing main core no. 3 and 4. See Figure 6.13 A that gives Cs as an example. This is confirmed by the NA analyses for Cs, Eu (Nd, Th) and U. See Figure 6.13 B that gives Eu as an example. All results from the surface analysis of fracture A are given in Appendix 9 Figure 1-3. The increased concentration can be traced to a distance of about 0.5 m, which is the end of the cored out fracture.

A. Cs AA

Scale

30lppm 20 10 I

Background

Scale 2.Qlppm to I

Background

59

3 4

0 -

\

3 4

B. Eu NA

Figure 6.13. Examples of surface concentrations on fracture A.

60

Analysis of penetration depths in fracture A.

The results from the analysis for the penetration depths show three major kinds of patterns, namely:

• Constant low level with depth. Indicates no sorption. See Figure

6.14 A.

• Declining concentration with depth. Indicates sorption within the

rock. See Figure 6.14 B.

• First inclining then declining level with depth. Indicates sorp

tion and partial desorption. See Figure 6.14 C.

There are several effects that can cause misinterpretation of the

penetration depths of the tracers and the corresponding parameters.

Among these one could mention surface roughness, carry-over during

sample preparations and a mineral content that varies with distance from the fracture surface. A variation of the mineral content with

depth wi 11 mostly affect the magnitude of the sorption and not cause false concentration profiles with depth. The two other effects may

induce concentration profiles which do not exist in reality. The magnitude of the two later effects have been investigated and the results are given in appendix 14. To summarize the results one can say that there is little or no carry-over in the sample preparation

equipment and the effects of surface roughness make it very difficult

to determine any Kd and De values from obtained profiles.

All results from the analysis of the penetration depth in fracture A

are given in Appendix 10 Fig.1-7.

Sample cores outside the area around the injection hole

Beside fracture A and its surroundings sample cores were taken from

randomly chosen points on other fractures in the main cores. The main

part of the samples were analysed by AA, for the surface content of Sr

61

and Cs. Eight sample cores were picked out for examination of

concentration variation with depth for Sr and Cs. Neither the surface

- nor the depth analysis showed any significant concentration level above the "background ... NA analysis have been performed on seven of the surface samples. In some of the samples the concentration level of an individual tracer is high, but as the levels are high for different tracers at different spots it is hard to draw any conclusions from these results.

The results for the surface concentration are presented in Appendix 9 Figures 4-8 and the results for the concentration variation with depth are presented in Appendix 10 Figures 9-10.

62

Concentration [ppm]

r-'1

= E. 2.0

A. Sample core no. 14

Concentration [ppm]

0 fD

""0 ('1" 1. 0 :T

r-'1

= 2. 0 = L-J

B. Sample core no.9

Concentration [ppm]

0 fD

""0 ('1" 1. 0 :T

r-'1

= 2. 0 = L-J

C. Sample core no.20

Figure 6.14 The three major patterns of concentration variation with

depth, exemplified with Cs from Atomic absorption analy

ses.

6.5.4

'E 0..

..9-

c .2 .., c L

"" c 01 0 c 0 u

63

Surface concentrations (measured)

The following figures show the obtained 11 surface 11 concentrations

versus distances from injection point. The thickness of the surface samples varies from 0.1 to 0.5 mm.

200 r-------------------------------------------------------------~

...

150 -

* * * 100 ... *

* * ...

* ... ...... * * ... ...... ** * ..... * * 50 f-**• • * * * ........ * * * * 411* * ... * * ... * * * ** ............. * * * * .. ...... ** * * * * * * * *- * * * ** * * ....... • * *

* 0 I I I

0 1 2 3 4 5

Distance from injection point [mJ

Figure 6.15 Surface concentration Sr.

'E a. .9-

c ~ ..., 0 t.. ""' c: 01 0 c 0

u

2SO

200 f-o

lSO f-o

100 f-o

so 1-

...

... .. -... .. ... - .. ... *

":H:.- * * ~ ":-. -:--.... *

0 0

Figure 6.16

300

...

2SO

'E 200 r-• a. .9-

c a :;; 0 t..

""' c (J 0 c 0 u

1SO

100 - .. *

........ ..... so - .. .

* ... ~ ... *

:... * '* 0 0

Figure 6.17

* I

64

*' ... ** .. .. • .. -· • ........... .. ... * ... .. * ..

I ..

I .. .. .. .. .. ..

2 3 4 s Distance from injection point [mJ

Cs AA analysis

...

* ..

* ... ...

* I* I I

2 3 4 s Distance from injection point (mJ

Cs NA an a 1 ys i s

25

20 ,_ ...

'E 0.. B- 15

c 0 .... ~ 0 ... L ~ c

10 ... (II 0 c 0

u

5 *

... l** ...

!.t*iitt* ... ill- ... ...

0 0

Figure 6.18

600

500 r- *

,..., 400 E .. a. B-

c 411-~ ... ~ 300 0 L ~ .. c (II

... u ... c 0 200 -... u ... ...

... .. * ...

100 - ......... ...

* .. ...

0 0

Figure 6.19

... *

...

...

65

2 3

Distance from injection point [m]

Eu

.. '"'

... ...

I

2 3

Distance from injection point [m]

Nd

4 5

4 5

66

60 * *

* *

* * * * -·· * * *

'E 40 -· * * a. * ..9- ·- * c a .... * ...,

0 * L ..., * c * CJ

* 0 * 1: a 20 • u

*

0 I I I

0 1 2 3 4 5


Figure 6.20 Th

700

600 t-*

500 'E * a.. ..9- *

400 * c * 0

"Z -0 L * ..., c 300 * Ill * 0 * c *# a u * *

200 # * * * * **

* * * 100 * * * *

* • 0 I

0 2 3 4 5


Figure 6.21 u

67

6.5.5 Mineral analysis

Ten sample cores were analysed for their mineral composition. An attempt to relate Sr "background" content to the mineral composition gave no clear connection. The results and further discussion are given in Appendix 11. Fig. 6.22 shows the span of the content of the different analysed components.

70 r. Maximum

bOOOa 60

Minimum so

lZ/ //..I 40

30

20

10

0

Quarts Plagioclase K-felspar Mica

Mineral component

Figure 6.22 The span of the content of the different mineral components, ten samples.

6.5.6 Determination of the effective diffusivity, De

To determine the effective diffusivity laboratory runs with iodide were performed. The results for the samples from fracture A are very close ranging from 1.1•10- 13 to 1.7•10- 13 m2/s. A short description of the experimental design and of all results is given in Appendix 13.

68

6.6 Comparisons between models and experiments

The modelling consists of two parts, namely:

o determination of fracture properties using the resu 1 t s from the conservative tracer runs

o prediction of the behaviour of the sorbing tracers.

6.6.1 Determination of fracture properties

Two different model concepts have been used when fitting to the experimental data, one without matrix diffusion and one which includes matrix diffusion. When fitting the models a single channel with a channel breadth of 1 m has been assumed.

The advection-dispersion model (A-D)

The transport parameters obtained when fitting the models to the experimental data are given in table 6.6.

Table 6.6 Hydraulic parameters from the A-D model

Samp 1 h.

2-6 2-8

Pe

1.96 0.86

336 710

3.0 10.5

69

Figures 6.23 and 6.24 show how the model could be fitted to the obtained breakthrough curves.

6

5

'E 4 a..

..9-

c 0 .... 3 ~ c L. ~ c 01 u c 0 2 u

500 1000 1500 2000

Time from start of injgction (h)

Figure 6.23 Fitted curve and experimental data from sampling hole

2-6.

1.50 r-------------------------------------------------------~

1. 25

'E 1. 00 a..

..9-

c .3 • 75 ~ c L. ~ s:: 01 u c 0 • 50 u

• 25

1000 1500 2000 Time from start of inj9ction (h)

~:!':_!urc 6.24 Fitted curve and experimental data from sampling hole

2-8.

70

The advection-dispersion-matrix diffusion model

The A parameter

(5.2.29)

which lumps the interaction with the surface and with the rock matrix, could be determined in two ways, namely:

1. by the fitting of the model to experimental data (four parameter fitting, one of the parameters is A)

2. by calculation of A based on results from independent laboratory experiments (three parameter fitting, A known)

Table 6.7 Transport parameters from the A-D-D model four parameter fit

Sampling hole

2-6 2-8

Pe

2.46 36.9

t w

279 44.5

2.7 8.5

A*

3548 133

Table 6.8 Transport parameters from the A-D-D model three parameter fit

Sampling hole

2-6

2-8

Pe

2.33 1.16

t w

293 548

2.8 10.5

A*

4926 30000

* A small value of A indicates a large interaction.

71

The four parameter fit gives a value for the A-parameter of 3500 for

the sampling hole 2-6. A difference of a factor 1.4 is obtained for

this parameter when the porosity and the effective diffusivity deter

mined in the laboratory are used as input to the model (three para

meter fit). On the other hand the A-parameter for samp 1 i ng ho 1 e 2-8

was found to be 133. This a value indicates a very high interaction

with the rock matrix. If instead the A-parameter is calculated from

laboratory data a value of about 30000 is obtained. The seemingly high

interaction with the matrix in the four-parameter fit for sampling

hole 2-8 may be due to the presence of stagnant water zones into which

the tracer can diffuse. Similar effects as matrix diffusion may be

obtained if the tracer diffuses into stagnant water, Moreno et al.

(1983). The unrealistically high value of tw for the three parameter

fit for sampling hole 2-8 is due to the low Pe that is obtained in the

fitting as there is considerable covariance between these entities.

Figures 6.25 and 6.26 show how the advection-dispersion-matrix

diffusion model could be fitted to the obtained breakthrough curves in sampling holes 2-6 and 2-8.

6~------------------------------------------------~

,...., 4 E

Cl...

.9-

c: 0 -;; 3 0 I.. ., c: Ql 0 c: 0 2 u

~- ············· ············--

1000 1500 2000


Figure 6.25 Fitted model and experimental data from sampling hole

2-6.

72

1.50 ~--------------------------------------------------~

1. 25

'E 1. 00 a.

..9-

c 0 ;; • 75 0 1.. ..., c 01 0 c 0 .so u

.25

500 1000 1500 2000

Time from start of injection [hJ


2-8.

The channelling model

In the case of the channelling model only advection and diffusion into the rock matrix are taken into account. There is no mixing between the

separate channels.

The output from the channe 11 i ng mode 1 is a function of four parameters, namely:

1 0'1 standard deviation in the lognormal distribution

2 Do = (DeKdpp) 1/2

3 tw water residence time

4 Pf dilution factor.

The fitting have been done in two ways, one with a fixed Do (three

parameter fit) and one where also o0 was fitted (four parameter

fit).

73

As can be seen figures 6.27 and 6.28 it is possible to get as good a fit as when using the other models. The flow parameters are given in

table 6.9 and 6.10.

6 r-------------------------------------------------------~

5

1'"'"1 4 E 0.. 0..

"--"

a 3 .... ...., 0 (.. ...., ffi 2 (.) c 0 u

500 1000 1500 2000

Time from start of injection [hJ


2-6.

1.50 ~-------------------------------------------------------,

1. 25

lt.OO 0..

"--"

c .~ • 75 ...., 0 (.. ...., c QJ g .so 0 u

• 25

0. 00 0 500 1000 1500 2000


Figure 6.28 Fitted mod~l and experimental data from sampling hole

2-8.

74

Table 6.9 Transport parameters from the channelling model three parameter fit

Sampling hole

2-6 2-8

Table 6.10

Sampling hole

2-6 2-8

.40

.47

Transport parameter

0"1

.36

.17

t w

348 530

parameters fit

t w

291 90

2.8 11.5

2.65 2.65

from the channelling model, four

pf

2.5 8.4

o0

• 10 7

7.88

48.49

6.6.2 Prediction of the behaviour of sorbing tracers

When predicting the behaviour of the sorbing tracer the advectiondispersion-matrix diffusion model concept was used. Two different inlet boundary conditions were used in the calculations of

o the breakthrough curve for Sr

o the surface concentration of the sorbing tracers

o the penetration depth into the matrix.

75

The prediction of the breakthrough curve for Sr

In figure 6. 29 a set of ca 1 cu 1 ated breakthrough curves for Sr are

shown with different Kd values. The outlet is taken to be at sampling hole 2-8 .

• 10 ~------------------------------------------~r-----~

.08 Kdp=30 De=l.35E-13

0 --- Kdp=lO De=l.OOE-12 u ....... 8

c 0 .06 -;; c L ., c Ql 0 c 0

• 04 u Ql > /' :;:; / 0 / w /

/ cc /' • 02 /

/' ~

~ /'

~ ...-...-0.00

0 1000 2000 3000 4000 5000 6000

Time from start of experiment [h)

Figure 6.29 Ca 1 cul ated breakthrough curves for Sr with different Kd values.

It can be seen in figure 6.29 that for both Kd values, Sr would have

arrived at the sampling hole in a well detectable concentration. In

the calculations no surface sorption is included in addition to the sorption in the matrix.

It was predicted that none of the other sorbing tracers were going to

arrive at the sampling holes during the duration of the experiment.

Calculation of surface concentrations

With the surface concentration here is meant ~he ,·:12C:d1 concentration in

a 0.4 nm layer, which is the average depth of the i"irst sample ground

off from the small sample cores. The predict~: concentrations for

76

various Kd values are presented in the following figures together

with the calculated results assuming 400 h leaching.

c a .., 0 L ., c Q! u c 0 u

200 ~--------------------------------------------------------------.

~-*'-., .,

150 .... ·-.......

100

·-....... . .........

1---- ., I', - - .,_

., -- '· ··-....... - ~-......... * * * ., -. . , ~~

·-.......... , * ..._ * *

Legend

* .. ...........~.:::-... ---------- * -....::...::::::::.._.._

Kdp=30 De=1.3E-13 Leached Kdp=10 De=l.OE-12 Leached

----- . ~~----,..-. - :.::::.-. * L ... ~ * * ~---...... --....::::... ___ - ... v; ** * * -;-.__ ·--.:::::.. -

50 1--•. * * ----- * ·-. ..... ** * --.-.......... ---. * ·- * * * ** * * .. • -· * * * * * lit•••••• *** * * * - * * • ** ......... * *


* * * * *

Figure 6.30 11 Surface 11 concentration of Sr, experimental data and

calculated data.

In figure 6.31 the predicted surface concentration by the numerical

method both using linear and nonlinear isotherms are compared.

"-UU ~ ·---·-------------------------------------.

Legend

ltnliiClr

L t near 1 eached 150 Expn. 0. S

Expn. 0. 5 l Qached 'E a. .9-

c 0 ;; 100 0 1.. ... c Cl u c 8

so

Distance from Injection point [mJ

Figure 6.31 Comparison between predictions of using a linear and a

non-linear isotherm.

77

It can be seen in figure 6.31 that the nonlinear isotherm for Cs makes the surface concentration profile steeper as expected because the Kd value is higher at lower concentrations.

The prediction above are based on the assumption that there is only one channel with a breadth of 1.0 m. As there is channelling within a fracture some parts of the fracture have not been in contact with the water containing the sorbing tracers and will therefore only have background con cent rations of the tracer independent of distance from the injection point. To show the difference in surface concentrations due to different assumed geometry at the injection point the numerical

method has been used to simulate the conditions in a channel with a

breadth of 0.1 m. The results for the two channel breadths and for different Kd values are shown in figure 6.32.

1.0~--------------------------------------------------~

c:. 0 :;:; 0 L ~ c: 01

.8

.6

g .4 0 0

CJ > ~ 0 -~ .2

Legend


Kdp=300 b=O. 1 Kdp=3QQQ baQ. 1 Kdp~:300 b•l.O Kdp=3000 b ... l.O

Figure 6.32 Comparison between predictions assuming different channel breadths.

As can be seen in figure 6.32 the sorbing tracers migrate further down the fracture assuming a narrower channel.

78

The difference between the so 1 uti on with the constant con cent ration

boundary condition and the solution with the constant injection

boundary condition is largest close to the injection point. It cannot

at present be decided which of the two boundary conditions is more

correct.

Calculation of peneteration into the rock matrix

Independent of assumed boundary condition, the concentration profiles

into the rock matrix look the same. They only v-ary in magnitude.

Figure 6.33 shows the typical profiles obtained with and without

leaching.

1.0 ......... -----------.. 1. 0.----------------.

~.a • "C i!S

...... 8 u ~

.6 .6

~ c 0

.6J ~ 0 L .6J c c

i·4 g.4 B Cl ~ >

i :::; D :i .2 :i .2

0.00 2 9 4 5 o.oo 2 5

Oapth [a.] Oapth [M)

Figure 6.33 Con cent ration vs. depth for a non leached and a 1 eached

place.

The height of the bars in figures 6.33 and 6.37 is the concentration

that would be obtained if samples with corresponding depths had been

taken.

There is a difference in the calculated concentration profiles for the

two boundary conditions in the close surrounding of the injection

point, figure 6.34.

79

1. Or--------------.

Legend -- Kdp=lO

--- Kdp=30

--- Kdp=300

------ Kdp=3000

2 3 4 5

Depth [mmJ

1. o..--------------,

;a. 8 ~

* 0 8 ....... u .....

• 6 c 0 :;; 0 L ..., c (II

g.4 0 0

\ \ \ \ \ \ \

\

'

Legend -- Kdp=10 ___ Kdp=30

--·- Kdp=300

--·---- Kdp=3000

...........

2 3 4

Depth (mmJ

Figure 6.34 Concentration vs depth, for the constant concentration and the constant injection boundary condition.

Figure 6.35 shows the calculated concentration profiles, using the analytical solution, for various KdPp values and at different distances from the injection point.

1.0..------------,

Figure 6.35

Kelp [m3/m3J

--10 ---30

--- 300 --·- 3000

Depth [mml

Solution for different from injection point boundary condition.

1.0.....-------------,

KdPp for the

X [m]

--0.1

- -- 0.5 ---1.0

-·-·- 2.0

3

Depth [mml

5

and different distances constant concentration

Figure 6.36 shows the same as figure 6.35 but here the calculation is made with the constant flux boundary condition.

80

1. 0..-------------.

Legend -- Kdp=lO

--- Kdp=30

-·-- Kdp=300

------- Kdp=3000

2 3 4 5

Depth (mmJ

1. Or-------------,

~.8 ::.:: * 0 8 ' 8

.6 c 0 .... ~ 0 L ~ c Ql g.4 0 0

Ql >

Legend -- X=O.l

--- X=0.5

-·-- X=l.O

------- X=2. 0

2 3 4

Depth [mm]

5

Figure 6.36 Solution for different KdPp and different distances from injection point for the constant flux boundary

condition.

Comparison with experimental data

It is very difficult to quantify the Kd values for the sorbing species due to the large variation in the experimental data. The variation is caused by many factors, it includes variations in the background concentration of sorbing species both along the fracture and perpendicular to the fracture, channelling, amount of leaching, uneveness of the fracture surface and variation in mineral content, which may cause the sorption properties to vary.

Figure 6. 37 shows how the thickness of the s amp 1 e ground off determines the possibility to detect leached profiles at high Kd values.

The profile has its peak very near the surface. Because it is necessary to grind off at least 0.2 mm to get a large enough amount of sample, the details in the peak location disappear, figure 6.35 b. When 0. 4 rrm have to be ground off because of 1 arge surf ace roughness

or other reasons the profile becomes even more smeared. The fitting of

the theoretical depth profile becomes insensitive to the sorption coefficient for large sorption coefficients.

81

1. Or------------, 1. Or-------------.

;a. 8 f-:X:

* 0 8 ' 8

.6 c 0 ..., 0 L ..., c 01 g.4 0 (J

01 > :; 0

~-2

0.0 ~ 1\ .I

2 3 4 5 0 2 3 4 5 Depth [mm) Depth [mml

Figure 6.37 Calculation of profiles obtained with different sample thicknesses.

As can be seen in figures 6.33 to 6.37 the output, from the fitting of the Advection-Dispersion-Matrix diffusion model to experimental data, will vary depending on assumed boundary conditions and thickness of sample. Another limitation is that C(t) for a given spot at the fracture surface is unknown and depending on channelling and Kd. All this adds up to that the obtained concentration profiles with depth gives a qualitative and not a quantative description to matrix diffusion and sorption within the matrix.

Determination of Kd from measured concentration profile

One of the sample cores was taken at a point on the fracture surface that was covered with glue. This spot has probably not been subjected to leaching.

The following assumptions were made when calculating the Kd values from experimental data, namely:

o The rock matrix could be treated as a semi infinity slab

82

o There is a linear relation between concentration in the fluid and

the concentration in the rock matrix

o The pre-injection concentration (background) is constant within the rock matrix

o There was a step change at time 0 in the con cent ration at the fracture surface (this applies strictly only very near to the inlet of the fracture)

o No leaching has occurred.

The solution to the Fickian diffusion equation for the appropriate initial and boundary conditions:

C = C0 Kd erf c ( x ) I Da•t

This equation was fitted to the experimental data for Sr. 1. 0.------------.,

g•B ::.::: * 0 8 ...... 8

2 3 4 5

Oepth [mm)

Figure 6.38 Experimental data and fitted curve.

83

The fitting gave a KdPp of 30 m3/m 3 and a De of 1.35•10- 13

m2 /s. The obtained Kd value is in the upper range found in litera

ture and De is the same as has been found in independent diffusivity

measurements of the Stripa granite. This exercise has been performed

only to see that the obtained profiles will give realistic values on

Kd and De and not to determine actual values for the Stripa granite.

84

DISCUSSION

7.1 Experimental design

When there are channels within a fracture, there is always a risk that the injection point is placed in a low conducting or not conducting part of the fracture. To minimize this risk several injection points within the fracture should be used.

An injection with an overpressure close to the natural pressure caused problems with the injection flow rates. Small variations in injection pressure caused large variations in the injection flow rates.

Injection of tracers with a constant injection flow rate is preferred to injection with a constant pressure. It is more convenient to evaluate the results from an injection with constant flow rate.

This type of experiment seems to be well suited to get a better understanding of the water flow in individual fractures (main flow paths).

There are some inherent difficulties to interpret tests with sorbing tracers. At least some of the difficulties could be avoided if radioactive tracers could be used. The use of radioactive tracers would, however, have made it very difficult if not impossible to excavate the fracture.

Some of the main difficulties are listed below.

1. The natural content of tracers (background) varies over the fracture surface

2. The mineral composition of the fracture surface varies. Kd

values for the different tracers are strongly dependent upon the mineral composition, Vandergraaf et al. (1982), Torstenfelt et al. (1983), Pinnioja et al. (1984)

3. The fracture filling 3nd coating materials vary in thickness

85

4. The surface of the small sampling cores were rather rough. On some

samples there was part of the surface left even though .1-.5 mm

had been ground off

Even with these difficulties it has been possible to detect surface sorption as we 11 as penetration of tracers into the surrounding rock

matrix in a real environment.

From the end of the inject ion of the sorbing tracers to the start of

the core drilling, there was a risk that some of the sorbed tracers

would be leached out. It was assessed that the loss of the sorbing

tracers would be small due to the presence of the injection hole which

was a sink which drew in most of the water before it reached the part

of the fracture that had been used in the experiment. The glue,

Loctite 470, that was injected after the injection of the sorbing

tracers completely sealed off the fracture from the injection hole and

the sink never developed. This made the effect of the leaching larger

but the parts of the fracture surfaces that were covered with glue

were not leached at a 11.

7.2 Pressure pulse testing

The hydraulic tests were not intended to be used to evaluate transmissivities and storativities. They were designed to locate and

pinpoint a fracture with high enough conductivity in the primary

injection hole H2 to be suited for tracer injection. They were also

used to test for connections or lack of such between various points.

The equipment used was not designed to minimize water volumes in the

monitoring points. The storativities obtained from the tests may

therefore be influenced by the compressibi 1 ity of the water not only

in the fractures but also in the holes. The hydraulic transmissivities

determined from the Q vs. t curves are much less sensitive to stagnant

water volumes and can be expected to be more reliable.

The hydraulic transmissivities determined from the "steady state 11

heads agree well, with those determined from the pulse tests.

86

The fact that one ho 1 e - H2 - intersected the fracture at a point

where the transmissivity was more than one order of magnitude larger

than in the other 4 intersections, indicates that the fracture has 11 closed 11 and 11 0pen 11 parts. This is consistent with other observations of 11 Channeling 11

•

7.3 Conservative (nonsorbing) tracer movement

The breakthrough curves from the first and second injection of

Uranine, at point H2, differs considerably. This difference may have

several causes, namely:

1. There has been a change in the flow system during the experiment.

2. The second injection performed with a lower injection flow rate

did not reach as far out sideways as the first and did not reach

the same channels as the first injection.

The first a 1 tern at i ve cannot be tested now. The second a 1 tern at i ve is

a distinct possibility in a channelling environment. It was observed

from the response to the second injection of Eosin, at point H3, where

the injection flow rate was constant during the injection, that

several distinct channels from injection point to sampling points can

be seen to exist.

The simultaneous injection of Uranine and Iodide shows no large

differencies in the behaviour of the two tracers. The absolute con

centration of Iodide in the sampling holes was low, so the resolution was poor.

7.4 Fracture widths

When calculating the fracture widths from residence volume it is

assumed that the injected tracer directly enters the main flow which

also is assumed to be constant over the whole channel breadth. This

means that the residence time for all water coming out at the sampling

point is the same as the time for the tracer. If one instead assumed

that the injection flow travels in a slow channel with a small flow

87

and meets the 1 arge flow near the samp 1 i ng point, the mixing occurs close to the sampling point and the calculated fracture widths would be reduced by a factor up to 3 for samp 1 i ng ho 1 e 2-6 and by 11 for sampling hole 2-8. This would reduce the difference between fracture widths calculated by residence volume and cubic law somewhat but this still does not explain the very small fracture widths obtained when

using the pressure drop and residence time as input. Figures 7.1 a and b show the two different channel configurations of the analysis above.

Figure 7.1 a) The injected flow Qinj mixes with the the channel directly at the injection residence time of flow LQ is obtained.

natural in point. True

b) The mixing occurs at the collection point residence time is that of Q;nj only.

88

In the tracer test in Finnsjon (Moreno et al., 1983) the fracture

width determined by the residence volume was about 6 times greater

than the value determined using the cubic law. The fracture widths

were 1.06 mm and 0.15 mm in this experiment.

7.5 Dispersion

For the tracer test 2-6 the dispersion length was about 1.9 m (Peclet

numbers were 2.3 and 2.5). In the test 2-8 these lengths were 0.12 m

when four parameters were fitted and 3.9 m when the fit included only

three parameters. (Peclet numbers were 36.9 and 1.16 respectively).

The low dispersion may be explained by the low value of the A-para

meter. A part of the spreading of the tracer pulse is taken into

account by diffusion into the matrix and is thus not included in the

dispersion.

As a comparison, in tracer tests at Finnsjon (Moreno et al, 1983) the

dispersion lengths were 0.34 and 5.7 m, for four and three parameter

fits respectively (Peclet numbers were 87 and 5.2).

The values of cr for channelling dispersion were about 0.38 for the

tracer test 2-6. For the test 2-8 these values were 0.17 and 0.47 for

four and three parameter fits respectively. For the tracer test at

Finnsjon the values of cr were 0.072 and 0.285 for 4 and 3 parameters

fits.

These comparisons show that the Stripa tracer test 2-8 has a lower

dispersion length than the tracer test at Finnsjon. On the other hand

cr is higher in the tracer test at Stripa. One large difference between

the tests is the different trave 1 1 engths used in the test ( 4. 5 m at

Stripa and 30m at Finnsjon). Neretnieks (1985) compiled available

dispersion results from experiments in crystalline rock. These seem to

indicate that the dispersion length increases with the distance.

89

7.6 Sorbing tracer movement

One of the problems with most of the sorbing tracers is their low solubility in groundwater. Even though the tracers may dissolve in the injection water, the chemistry within the fracture may change with distance from injection point. This change may cause a decrease of the solubility and the tracers may precipitate. On the other hand having very high concentrations of tracers may also change the chemistry of the water within the fracture and thereby the behaviour of the tracer.

Of the six injected sorbing tracers only the following four were found in concentrations which were well enough above the background to be sufficiently distinguishable from the natural concentrations in the

rock.

o Cs, Sr, Eu, U

The very low solubility of Th, made it impossible to detect any sorbed amounts. The sensitivity of the Th and Nd analyses was also less when there was a high concentration of U in the same samples.

Another problem is the very large variations in the natural content of the sorbing species even over short distances. Several investigations

a 1 so report a dependence of Kd on the miner a 1 content. Samp 1 es of the fracture surface and the adjacent rock show large variations of mineral content. All these natural variations makes it very difficult to determine Kd values with any accuracy. However, many of the s amp 1 es taken from the fracture surf ace and the adjacent rock show elevated concentrations of the sorbing tracers and in several cases even a concentration profile in depth can be found. These elevated concentrations are clearly due to the presence of the injected

species.

One way to overcome these problems would be to sample the complete fracture surface as well as the adjacent rock. This would probably make it possible to determine an overall Kd value for each of the tracers. The drawback is economy, it would be tremendously expensive.

90

Another way would be to use radioactive tracers instead, but this will make the excavation of the fracture and the handling of the samples very complicated if at all possible.

From the sampling of the fracture surface it can be seen that there is a rise in the concentration of the sorbing tracers at a distance of about 2 m from the injection hole. If this is due to local variation of the natural content or if there has been a channel within the fracture that had a very small surface area and thus less retardation of the sorbing tracers cannot be determined.

7.7 Modelling

Three different models have been used to analyse the experimental data:

1. the advection-dispersion-surface sorption model

2. the advection-dispersion-matrix diffusion model

3. The advection-channelling-matrix diffusion model.

The first model has been used to investigate if it is possible to get a good fit to the breakthrough curve for the conservative tracers by assuming no matrix diffusion. Both laboratory experiments Skagius and Neretnieks (1983), Andersson et al. (1982) and field experiments, Birgerson and Neretnieks (1982, 1983), have shown that matrix diffusion takes place in crystalline rock. The concentration profiles in the rock matrix obtained in this experiment also show that

diffusion into the rock exists under real conditions.

With diffusion into the rock matrix the recovery of even a conservative tracer will never be complete because some tracer will always reside in the porous matrix of the rock. An analysis of a breakthrough curve must take this into account.

91

diffusion 1000 1500

matrix diffusion-=--------- _ 500 1000 1:;o(l 2000

Channelling SilO

Figure 7.2 Sampling hole 2-6. Different models fitted to experimental data.

!.SO

1.25

1.00

I. SO

.75

1.25

.so 1.00

I.SO ......--------.25

.75 1.25

.so 1000 I SilO 2000

1.00

.75

.so

.25

SilO 1000

Figure 7.3 Sampling hole 2-8. Different models fitted to experimental

data.

92

As can be seen in figures 7.2 and 7.3 it is possible to obtain a good

fit with all of the models. They model different mechanisms. The fitting thus cannot differentiate between the mechanisms and the correct

mechanism(s) must be selected by some other process.

When predicting the breakthrough curve for the injected Sr, the frac

ture properties, assuming a channel breadth of 1 m, from the first

injection of Uranine has been used. As could be seen from the second

injection the properties were not the same, so some time during the

injection of the sorbing tracers the properties of the channel have

changed gradually or momentarily. If clogging of the flow paths is the

cause of change it probably occurred gradually. If on the other hand the change in properties is due to the decrease of the injection flow

rate this decrease occurred before the injection of Sr and the prediction of the breakthrough curve shou 1 d be based on the fracture

properties obtained from the second injection of Uranine.

The calculated surface concentrations and the concentration profiles within the rock matrix could partly be confirmed by experimental data.

They show sorbing tracers concentration profiles which can only be

explained by matrix diffusion. The different types of profiles with

and without leaching were also found experimentally.

The two different boundary conditions used for the advection-dispersion-matrix diffusion model, only showed differences in the vicinity

of the injection point. Further down stream the predicted concentra

tions converged.

The analytical solution for the ADD model (equations 5.2.25 and

5.2.30) was determined using a constant concentration at x = 0. When

this condition is used, the tracer is also transported into the

fissure by hydrodynamic dispersion during the injection. When the injection is interrupted the direction of the tracer flow due to this

mechanisms is just the opposite.

93

The boundary conditions play an important role when the concentration

is calculated at locations with a low Peclet number. The equation

(5.2.30) used to calculate the concentration in the matrix is a poor

approximation for points near the injection hole. Due to this difficulty a numerical solution was used (TRUMP code). The boundary condi

tions used were constant flux at the inlet and no dispersion at upstream (x ~· 0).

The advection-channelling-matrix diffusion model assumes a multitude

of separate channels. It cannot be used to predict the concentration

profile of a sorbing species within a fracture plane because every

separate channel has its own profile. It does, however, describe the

observed situation qualitatively very well, as it predicts that there

should be large variations in sorbing species concentration at the same distance from the injection point.

7.8 Concepts of water flow within a fracture

Available observations indicate that it is not realistic to treat a fracture as two planar parallel surfaces with a constant width (or

opening). Blocks of rock cannot hover over each other but have to have

points where they are in contact. A description of such a system has

been given by Tsang (1984) and the effect on the pressure drop when

water flow through such a fracture is also discussed. If this is the

only effect that causes channelling the direction and magnitude of the

channels would be randomly distributed and there would not be any preferred direction for the water flow. The water flowing in the

channels might, however, in some ways affect the channels, so that preferred flow directions might develop with time.

The channels cannot be expected to have the same breadth all along. In

some parts the channe 1 breadth may be so 11 1 arge 11 that it more seems

like a "lake" with a stream passing through. When the water passes

through such 1 akes there will be diffusion into the stagnant water

zones. This diffusion will give effects similar to those that occur

when tracer diffuses into the micro pores of the matrix. In other places the channels may be very narrow. The channels are probably

connected to each other but at present there are only very few

94

observations to substantiate this. The fact that tracers emerged in

collection holes 2-6 and 2-8 is an indication of mixing between channels.

If there is a preferred direction of the channels, the results of a tracer test must be different depending on if the induced pressure drop is perpendicular or parallel with the direction of the channels.

The present experiment has given no information which could be used to determine preferential flow directions.

With this concept of the fracture it is easy to see the difficulties to model the response of tracer tests in natural fractures in detail. The actua 1 mode 1 s used do not take into account stagnant water zones

(lakes). The channelling model used is also simplified to only account for channels which do not mix between inlet and outlet.

Our present concept of flow in a fracture is that there are different

channels which may mix their waters at irregular distances. The extent of the channe 1 s and the mixing distances are unknown at present. The

ch anne 1 s may have zones of stagnant of near stagnant water which may be reached mainly by diffusion. This is illustrated in Figure 7.4. The

matrix is porous and contains stagnant water in the micropores of the matrix which also are reached by diffusion only. Fissure coating or filling material may vary in composition and thickness as well as in porosity along the channels and influence the tracer transport. There

are models which account for all these effects but there is no model which takes them into account at the same time.

95

Figure 7.4 Concept of water flow in a fracture.

Some of the effects such as channelling, matrix diffusion and diffusion into stagnant zones of water influence the calculated

results in a similar way (e.g. long tailing of the breakthrough curve) and these effects cannot be distinguished from the analysis of

breakthrough curves only. They must be assessed by independent observations.

In the present investigation matrix diffusion was observed by direct observation of penetration depths, channelling was observed by using a large amount of collecting points. The presence of stagnant "lakes ..

was not observed directly but inferred from general observations on the necessity of points of contact between rock blocks.

96

8 CONCLUSIONS

The three natural fractures investigated show distinct channels where flow takes place with large areas where there is no or very little

flow in between. These channels have breadths of less than 1 m (this is about the reso 1 uti on of the water co 11 ect i ng equipment) . Pressure

pulse tests in the 11 plane 11 of the fracture also indicate that the opening varies considerably. Some of the tracer tests also show

channelling effects.

The single fractures which were seen very distinctly on the face of the drift cou 1 d not be projected over a distance of 4-5 m into the

rock. At the point where the injection holes were expected to intersect the fracture plane there often was no open fracture even if

sometimes the TV logging showed fractures with similar angles as the

projected fracture. Open fractures could only be located by hydraulic

testing and not by core logging or TV inspection. What seems to be a

single fracture at one location often consists of several fractures

further away. Some of these fractures are closed.

The fracture surfaces are not smooth and are often covered with minor amounts of secondary minerals and clays. The granite is in some places

in the same fissure plane covered with much thicker secondary minerals than in others.

The observed fracture openings determined from the water vo 1 ume that

resides in the fracture is very much (order(s) of magnitude) larger

than what is needed to induce the observed pressure drops. This means

that hydraulic testing may not be used to obtain the actual flow porosity of a fissured natural rock using the presently available

interpretation methods. The errors involved may be up to a few orders

of magnitude.

The injected strontium did not arrive at the collection points as was

expected from projections based on laboratory data on non site

specific samples and the results from conservative tracer runs. Sub-

97

sequent measurements on samples from the test site lead to projections

which indicate that less strontium should arrive. It still should be

detectable if no other mechanism or pathways have been active.

St rant i um, ces i urn, europeum, and uranium were found sorbed on the excavated fracture surfaces at varying distances from the injection point. There are clear indications that they have not moved uniformly

down the fracture. Thorium and neodymium were not detectable above the high natural background concentration in the rock. This is an inherent difficulty in using these nonradioactive tracers as the background is high and the solubility of neodymium and especially thorium is very

low.

The samples which were ground off in depth give clear indications that the sorbing species have migrated into the rock matrix and can be

found sorbed on the minor surfaces of the rock. Because of the

considerable surface roughness it has not been possible to asses the transport properties from the samp 1 es of the surf ace but laboratory measurements on samples taken from the actual fracture surfaces give

consistent information.

98

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Abelin, H., Gidlund, J., Moreno, L., Neretnieks, I.: 11 Migration in a single fracture in granitic rock 11

• Scientific Basis for Nuclear Waste Management VII, p. 239, North-Holland 1984.

Abe 1 i n , H . , G i d 1 u n d , Instrumentation and site report, in print 1985.

J.: "Migration description".

in a Stripa

single project,

fracture. I nterna 1

Abramowitz, M., and Stegun, I. A.: "Handbook of Mathematical Functions". Dover publications, New York (1972).

Allard, B., Kipatsi, H. and Torstenfelt, B.: "Adsorption of long lived radionuclides in clay and rock 11

• KBS TR 98, Nuclear Fuel Safety Project, Stockholm (1978).

Andersson, K., Torstenfelt B., Allard B.: 11 Sorption behaviour of 1 on g- 1 i v ed r ad i on u c 1 i des i n i g n eo us rocks 11

• In 11 En v i ron men t a 1 migration of long-lived radionuclides 11

• IAEA, Vienna 1982.

Bear, J.: 11 Hydrodynamic dispersion. Flow through porous media". (R.J.M. de Wiest ed.) Academic press, New York (1969).

Birgersson, L., Neretnieks, I.: Diffusion in the matrix of granitic rock. Field test in the Stripa mine. In: Scientific Basis for Nuclear Waste Management V, 519, Elsevier 1982.

Birgersson, L., Neretnieks, I.: Diffusion in the matrix of granitic rock. Field test in the Stripa mine. In: Scientific Basis for Nuclear Waste Management VII, 247-254, North-Holland 1984.

Carslaw, H.S., and J.C. Jaeger: "Conduction of heat in solids". 2nd ed., Oxford University Press, New York, 1959.

Edwards, A.L., "TRUMP: A computer program for transient and steady state temperature distributions in multidimensional systems". Report, Natl. Tech. Inf. Serv., Nat. Bur. of Standards, Springfield, Va., 1969.

99

Hantush, M.: "Hydraulics of wells ... Advances in hydroscience, vol 1, p. 281-432, 1964.

Lapidus, L., and N.R. Amundsen: 11 Mathematics of adsorption in beds". J. Phys. Chern., 56, 984, 1952.

Moreno, L., Neretnieks, I. and Klockars, K.E.: "Evaluation of some tracer tests in the granitic rock at Finnsjon 11

, KBS TR 83-38, Nuclear Fuel Safety Project, Stockholm (1983).

Moreno, L., Neretnieks, I., Eriksen T.: "Analysis of some laboratory tracer runs in natural fissures 11

• KBS TR 84-04, Nuclear Fuel Safety Project, Stockholm (1984). To be published in Water Resources Res. 1985.

Neretnieks, I.: "A note on fracture flow dispersion mechanisms in the ground. 11 Water Resources Res., vol 19, No. 2, 364-370, April 1983.

Neretnieks, I.: Transport in fractured rocks. Paper at the IAH 17th International Congress on the Hydrology of Rocks of Low Permeability. Tucson, Arizona, Jan 1985. Proceedings in print.

Neretnieks, I., Eriksen, T. and Tahtinen, P.: "Tracer Movement in a Single Fissure in Granitic Rock: Some Experimental Results and Their Interpretation .. , Water Resources Res., Vol 18, 849 (1982).

Pinnioja, S., Jaakkola, T., Kamarainen, E.-L., Koskinen, A., Lindberg A.: "Sorption of Carbon, Cobalt, Nickel, Strontium, I'odine, Cesium, Americium, and Neptunium in rocks and minerals". Nuclear Waste Commission of Finnish Power Companies, Report YJT-84-19, (1984).

Skagius, K., Neretnieks, I.: Porosities of and diffusivities in crystalline rock and fissure coating materials. In: Scientific Basis for Nuclear Waste Management VII, Boston, Nov. 1983, p. 835, NorthHolland 1984.

Skagius, K., Neretnieks I.: Porosities and diffusivities of some non-sorbing species in crystalline rocks. Report, Royal Inst. of Technology, Dep. Chern. Eng., Feb. 1985a.

Tang, G. H., Frind, E.O. and Sudicky, E.A.: "Contaminant Transport in Fractured Porous Media. An Analytical Solution for a Single Fracture ... Water Resources Res., Vol 17, 555 (1981).

100

Torstenfelt, B., Eliassen, T., Allard, B., Andersson, K., Hoglund, S., Ittner, T., and Olofsson, U.: 11 Radionuclide migration into natural fracture surfaces of granitic rock 11

• Mat. Res. Soc. Proc. Vol 15, p. 339-346, North-Holland 1983.

Tsang, Y.W.: 11 The effect of tortuosity on fluid flow through a single fracture. 11 Water Resources Res. 20, No. 9, p. 1209-1215, 1984.

Vandergraaf, T.T., Abry, D.R.M., and Davis, C.E.: 11 The use of autoradiography in determining the distribution of radionuclides sorbed on thin sections of plutonic rocks from the Canadian shield". Chemical Geology, Vol 36, p. 139-154, 1982.

101

10 NOTATION

A parameter defined in eq. 5.2.29

B parameter defined in eq. 5.2.31

B fracture breadth

Cf concentration in the liquid in the fissure

Cm concentration in the solid

Cp concentration in the liquid in the pores

Cs concentration on the surface of the solid

Cw concentration in the stagnant water

C0 concentration of injection fluid

Da apparent diffusivity

De effective diffusivity into the rock

DL dispersion coefficient

g gravitational constant

h hydraulic head

h0 hydraulic head in injection hole

Ka surface equilibrium constant

Kd mass equilibrium constant

Kd mass equilibrium constant based on solid proper

Kpf hydraulic conductivity of fissure

L channel length

Pf dilution factor

Pe Peclet number

Q flow rate

r radial distance

r 0 effective radius of injection hole

Ra surface retardation factor in the channel

Rd matrix retardation factor

S storativity of fissure

T transmissivity of fissure

m

g/m3

g/kg

g/m3

g/m2

g/m3

g/m3

m2/s

m2/s

m2/s

m/s 2

m

m

m

m/s

m

m

m

102

t time s

t 0 tracer residence time s

tw water residence time s

Uf water velocity m/s

x distance in the direction of flow m

z distance into rock matrix m

6 fissure width in the channel in the fissure m

£p porosity of rock matrix

~ parameter defined in equation 5.2.26

~ parameter in the lognormal distribution

p r/r 0

Pp density of rock matrix

Ps density of minerals

u

standard deviation in the lognormal distribution

T t S r 2

0

kinematic viscosity

kg/m 3

kg/m 3

- 103 -

APPENDIX 1

Location of fractures

The map below shows the location of the test site for the main

investigation and the two fractures utilized in this investigation.

X= 350

_j-MAIN . TEST SITE

X= 300

y = 1100 y = 1150 y = 1200

- 104 - APPENDIX 2

location of sampling holes at the main test site

View from above.

FRACTURE#2

FRACTURE#1

1m

- 105 -

APPENDIX 3

Eva 1 u at i on of the i n t e g r a 1 i n the ad v e c t i on-d i s per s i o.n-mat r i x d i f f u -

sion model

The integrals in equation (5.2.25) and (5.2.30) have no analytical solution and are evaluated numerically. To improve the integration new narrower limits are chosen. The maximum absolute error accepted in the evaluation of the integrand is defined as

1.0·10-6 E ~ ----=:....::....:.--=-::::___

Pe exp ( -2- )

To determine the lower limit, ~i is calculated considering that the

exponential function or the erfc function in the integrand is equal to e:. The greater of these two values gives the lower limit of the integral

l;? = Max 1

_ 1 n e: ( 1

_ 1 1

_ Pe 2

2 4 (lne:) 2

K_ 1 + I 1 - t

2

In the second case the Asymptotic solution for erfc is used (Abramowitz and Stegun, 1972).

The upper limit is calculated considering that the value of the

erfc function is less than 1.0. The upper limit of the integral is

ln Pe 2 ~} = - _e:_ ( 1 + I 1 - )

2 4 (lne:) 2

The numerical integration was done by means of Gaussian quadrature.

Typically 30-50 points were used to obtain a relative accuracy of 0.1 %.

- 106 -

The outlet concentration was measured about 500 times. In the fitting process about 50 points were used. To reduce the amount of points, the experimental data were smoothed first. The points used in the

fitting process were chosen to get a better distribution of the experimental data with time. The curves were divided into three parts. The same amount of points was used in each part.

- 107 .-

APPENDIX 4

Pressure responses and water loss rates.

t~~~~~~~~~~~:~~~~~~~~·

~ ~--~~+- --

t -- : --i.

1-- .

l .5:===========~-~----------~--4~++~~--+~-:-~+-~-~-+~~~~--------~-~-~~~-i~--"i 1----+- - - .... - . - - . . --. - -- -- I 1- - I -l I

100

Injtaction point 1 N2 15.77 11

~ point • H4 14. 7911

I .......... .. ..... ··· ·~· ..... '············ ······

1000 10000 100000

[bar] I

eo.nte 11 H3 INSTAll 15.18&. 5 bar INJ I N2 H3 H4 H5.. H4 H5 EH<EU4 UTAN=OR TAN<T SPRICKA.

I I . -- ---- ---"--

---- --··

cE I

I -• c ... I ... I

-~r---r-~~rn~---r-+-r++fH~~~4-+44+~--~~~~~~ ! -1.1..

.. ..

I

J

I I I

t 100 UXlO

TiM froa etart of in.)Qction [eJ

InjQCt1on point • N2 15.77 a

Wotar lou rate

.• .. UlOOO 100000

CoiiiQnte • H3 INSTALl 15. 18a. 5 bar INJ I N2 HS H4 HS. H4 H5 EN<El.M UTAt-FOR TANKT SPRICKA.

2.2

2.8

- 108 -

1

1----+---+--f··-f--+-+-H- f-- - . 1- - -

-·-·-···- -- - 1- f-

.,.._--f.--··· ~ ·- -- • - f-

100 1000

.. ~· .. ······ 10000

"- - 1 I

- 1-

·I-

······ .... 100000

Ti .. froa start of tnjaction tel

InJection point 1 N2 15. 77 •

Raeponee point 1 H3 15. 18 •

0v&r ~ [bar) I

Natural praeeur'Q [bar) I

Co.inte a H3 INSTALL 15. lS... 5 bar INJ I N2 H3 ~ H5. H4 H5 fJI<ELM UTAhFOR TANKT SPRICKA.

t ! ] .... -1

1 '. J 0 ~ . 1 . ' I ··-rTr ~ ' T l T l ' I ::: i l i I

! ! ! I i !

I ! l! I ! •

Tl'1 . i

' . 'I I i I .. ~- -~·,·-~ "1 .. 'I I;, . i I ! :I 1

ill i I

t '! I !i I i ! :I

I I 0

i--j ----- . , .. l·r·T I! ' I i ; I l l \ I

.5 l !

I : I I I I I I I

~- y- -~ I ,.; I

J_. ~-- . I

~---

I 1----· I --· ·-- 1-· --

··j··· ... .. .. . 0

10 .. ·········· ············ ······ ....

100 1000 10000 100000

Ti• fro• etart of inJection tel

In)iiction point • N2 15.77 •

Ri&epone& pot nt 1 52-8

tbor) •

Natura 1 pMitnUNI [bar) 1

Colliinte 1 H3 INSTALL 15.1S... 5 bar INJ I N2 H3 H4 HS. H4 HS ENKELM UTANFOR TANKT SPRICKA.

2.2

2.7

2.2

2.0

- 109 'I""

~--+-~-r~~~--~--+-~-+- I I

100

Injaction point • N2 15. 77 11

RaeponeG point 11 S2-9

.. ··I··· ......................... ······ .. .. 1000 10000 100000

to.nte 1 H3 INSTALL 15.18&. 5 bar INJ I N2 H9 H4 HS.. H4 H5 ENKE1..M UTAN=OR TANKT SPRICKA.

2.2

1 .. 8

- 111 - APPENDIX 5

Tables with results from the pressure pulse tests.

Table 1.

Injection in hole N2. Results from Q vs t measurements.

Location T TIS s h Test 0

in hole m21s m21s m

12.09 m } 13.52 m 5.5·1o- 10 1.4•10- 4 4.1·10- 7 67 820618

15.74 m 4.8·Io- 10 6.4·10- 4 7.5·10- 7 67 820701 15.77 m 6.54·lo- 10 1.8•10- 2 3.6•10- 8 21 821007 15.77 m 3.4·1o- 10 7.0·10- 4 4.8·10- 7 22 821008 15.77 m 2.8·1o- 10 6.1•10- 4 4.8•10- 7 23 821117

Table 2.

Hydraulic diffusivities TIS evaluated from responses in surrounding measurement points. Test 820618.

Injection in H2 at 12.96 m. h0 = 67 m.

Measurement rllro eff TIS rl ro point m m m21s

52-8 100 4 0.04 4.7•10- 3

52-5 >>100 4 <0.04 1.3•10- 3

H4 12.00 m 7 1.2 0.17 3.9•10- 4

H1 14.40 m 7 5.3 0.76 1.9•10- 3

H5 13.6 m >>100 4.2 <0.042 8.6•10- 3

HG2 12.34 m 10 0.62 0.062 3.9•10- 3

Compare TIS = 1.4•10- 3 from table 1.

- 112 -

Table 3.

Hydrauli.c diffusivities TIS evaluated from responses in surrounding measurement points. Test 820624.

Injection in H2 at 15.85 me h0 = 63 m.

Measurement rl/ro eff TIS rl ro

point m m m21s

S2-8 >>100 4 <0.04 1.6•10- 3

Sl-5 no response H4 12.00 m >>100 1.1 <0.011 1.3·10- 4

H1 14.4 rn >>100 5.3 <0.053 1.3•10- 3

HG2 12.34 rn >>100 3.51 <0.035 3.3·10- 3

1.5 <0.015

Table 4.

Hydraulic diffusivities TIS evaluated from responses in surrounding measurement points. Test 820701.

Injection in H2 at 15.74 m. ho = 73 m.

Measurement rllro eff TIS rl r 0

point m m m21s

S2-8 10 4 0.4 2.2 ·1o- 3

S1-5 very low response

H4 12.00 m 10 1.1 0.11 3.0•10- 4

H1 14.4 m 8 5.3 0.66 2.0•10- 3

HG2 12.34 m 10 3.4 0.34 1.2•10- 2

1.5 0.15 6.1·1o- 2

H5 13.6 very low response

- 113 -

Table 5.

Hydraulic diffusivities T/S evaluated from responses in surrounding measurement points. Test 821002.

Injection in H2 at 15.77 m. h0 =22m.

Measurement rl/ro eff T/S rl r 0

point m m m2/s

S2-8 100 4 0.04 3.0•10- 3

S2-9 100 4 0.04 1.1·1o- 3

H5 15.36 m 4.2 no response H3 15.18 m 3 0.8 0.27 3.3•1o- 4

H4 14.79 m 8 le1 0.14 I.s®Io- 4

H2 16.31 m no response

Table 6.

Hydraulic diffusivities TIS eva 1 uated from responses in surrounding measurement points. Test 821007.

Injection in H2 at 15.77 m. ho = 21 m.

Measurement rl/ro eff T/S rl r 0

point m m m2/s

S2-8 100 4 0.04 3.6•10- 3

S2-9 100 4 0.04 1.1•10- 3

H3 15.18 m 2 0.8 0.4 1.1•10- 4

H4 14.79 m 10 1.1 0.11 1.4•10- 4

H2 16.31 m no response

Hl 18.06 m >100 5.3 <0.053 6.9•10- 4

- 114 -

Table 7

Results from tests in holes Hl, H3, H4, H5

Injection Measurement r 1/r 0 r 1 r~ff T/S

point point m m m2/s TIS S Test m2/s

from Q vs t tests

H3 15.18 m 1.6•10- 11 - 821008

H4 14.79 m 821008a

H5 13.56 m - 821008a

H1 16.27 m H3 15.19 m >>100 5 <0.05 4.1·1o- 2 4.4·1o- 11 - - 821117b

H3 15.19 m H2 15.77 m >>100 0.8 6.3·1o- 4 ~ 4·1o- 11 - - 821117b

H4 14.83 m no responses in H1, H2, H3, H5 821117a

H5 13.71 m no responses in H1, H2, H3, H4 821117a

a) Water loss < 5 ml/h b) H2, H5, H4 gave no responses

- 115 -

APPENDIX 6

Data on main cores and fractures.

m Dsapth

Main cores in drilling order

Legend:

Missing oorts Grovel and sand Solid rock

Fig 1. Schematic view of fracture frequency and location in depth of rna in cores.

- 116 - APPENDIX 6

X-coordinate axis

97. 1 ~~ :\\~ (~all_

~ Injection point ( - 1--- f.--'""" ~ 10

~~ ~2~ Cb\: ? - 1/ r==rs-~----11 Jj_ 97.6

~ ---f-o-- - ~ ~ ~1) l\ch 2 11 I(,~\ ~t 7'~ f/1 s\ J::~ Fracture plane A

(, 14 1--13

"-l-J \_"_) 'r--~6) -1'-[>I

1.~ M ..

..... ~ 98. 1

221.7 221.2 220.7

Y-coordinate axis

Fig 2. Location of the main cores at the level of the injection hole. (Z = 349.6 m)

X-coordinate axis

/""'.

~~

~~ '1"2 ,~"0 {2 ~ r- - --'---

96.8

97.8

~ 14. 13

5 .....

.... 1'0 i _.

r

.....___ - ---- r-

98.8

223.8 222.8 221.8

Y-coordinate axis

Fig 3. Location of the main cores at the level of the face of the drift. (Z = 354.0 m)

- 117 -

APPENDIX 6

Main core no. 10 Ill Glue

Bottom of H2

Main core no. 5

Fig. 4. Location of fracture A and B, and the glue spots.

- 119 - APPENDIX 7

Table 1. Number of taken sample cores and performed analyses.

Analyses AA NA

Sample cores from Total Surface Depth Surface Depth ) 3 samples > 3 samp 1 es

Main cores 210 150 27 31 3 Injection hole 5 2 2 1 Water collecting holes

Fracture 1 5 4 1 1

Fracture 2 11 8 3

A total of approximately 325 atomic absorption analyses and 65 neutron

activation analyses were performed.

- 120 - APPENDIX 8

Tracer concentration in samples from the water collecting

holes.

AA

Sampling Core no. hole

Mean ground Sr Cs Cs Eu off depth ppm

(mm)

s 1-1 GO 0.25 55 -0.6 35 15 0.775 50 - 8 <0.4

0.95 35 -1.15 5 5

1.325 10 5 1.475 5 5

0 prov 0.025 20 5

0.1 20 5 6 <O .2

0.85 20 10 s 1-4 93 0.15 85 15

s 1-11 92 0.2 140 20

s 2-1 94 0.225 25 5

10.0 20 5

178 0.225 4 0.60 s 2-3 193 0.3 260 10

s 2-4 197 0.2 190 10 198 0.25 55 10

s 2-6 174 0.25* 7 2.9

10.0** 30 5

175 0.275* 380 10

0.675* 360 10

s 2-7 176 0.3 9 2.2

177 0.225 70 10

s 2-8 192 0.25 20 15 s 2-10 191 0.35 25 10

* Fracture filling material ** Under fracture filling material

NA

Nd Th u

65 45 170

40 20 35

42 28 37

173 41 94

181 30 31

- 121 -

APPENDIX 9

Surface concentration data

In the following pages the surface concentration of the five different tracers is presented.

Figures 1-3 show the surface concentration on fracture A.

Figures 4-7 show the surface concentration in samples from the main cores outside fracture A. Due to the large number of samples for Sr and Cs these results are only presented as a span of concentrations

from different areas of the main cores.

pre-injection surface concent. PPM

301 20 10 I


301 20 10 I

210

\

- 122 -

\


40! 20

I

APPENDIX 9

Fig. 1. Surface concentration of Sr and Cs on fracture A.

Eu

pre~injection surface concent. PPM 2.0 I to I

Nd


1001 so I

- 123 -

20 \

0

APPENDIX 9

\

\

Fig. 2. Surface concentration of Eu and Nd on fracture A.

- 124 -


301 20 10 I

u


1001 so I

APPENDIX 9

Fig. 3. Surface concentration of Th and U on fracture A.

ppta

Main core no. 1

ppm

Main cores no.2,5,6

ppm

Main cores no.3,4

.. • liD • til 81

ppm

Main cores no.7,8,9

125

ppm

Depth

.. . . "' . .. ppm

-

APPENDIX 9

.. • • • 111 ..

ppm

Main in dri 11 ing

/

\G Ull 1 .. 1418 I» 14 118 ... . . . .. . .... Ill ~ •• , .. .,.

ppm

Fig. 4. The span of the surface concentration of Sr in the main cores

outside fracture A.

t M ~ » a • d ~ • • • ~ n

PP"'

Main corliil no. l

~ /

~ .~ ~ 1'71

ppt11

Main cores no.2,5,6

~ ~ ~ v:

.~ / ~ • • • w u • ~ - n ppm

Main corQs no.3,4

pp•

Main coras no. 7,8,9

126 APPENDIX 9

Cs AA

. :~

ppm ppm

Depth

Main

/

~ ~ ~~ ~ .

I .. tS • II • Ja __ tt. .. ft .. . ,. " PP"' PP"'

-Fig. 5. The span of the surface concentration of Cs in the main cores

outside fracture A.

- 127 - APPENDIX 9

ppm

30

20

10

I Pre-injection surface concentrction

Cs NA Mcin cores in drilling order

Fig. 6. The surface concentration of Cs in the main cores outside fracture A.

- 128 - APPENDIX 9

3.0

2.0

1.0

PrQ-inJ~?cti f on cur OCI? concQntrct ion

ppm

300

200

100

PrQ · J -ln ection surfocQ concentrctior

Mcin corQs in drilling ordQr

Nd Mcin corQs in drilling ordQr

Fig. 7. The surface concentration of Eu and Nd in the main cores outside fracture A.

Th

APPENDIX 9 129 -

sur oce conc~ntrotion Pre-injection f

Moin cores in drill. »ng order

u Main cores in drilling order

Fig. 8. The surface concentration of Th and U in the main cores out

side fracture A.

- 131 -

APPENDIX 10

Concentration variation with depth

In the following pages the concentration variation with depth for the five different tracers is presented.

Figures 1-2 show the results for Sr anc Cs from fracture A.

Figures 3-7 show the results from neutron activation analysis for 5 sample cores from fracture A, one sample in each figure. Figure 3 (sample core No. 79) shows the pre-injection concentration.

Figure 8 shows the results from fracture B.

Figure 9 shows the results from the main cores outside fracture A and B.

200

2.0

3.0

2

25

- 132 -

10

3.0

1l

APPENDIX 10

23

30

0. orm~#~{>:m~iffi~:r-;~4~,;-~">t~i'W~'rJ 1.0

2.0

3.0

29

~~~·=·i~ 3.0 ~~:::::::~m ~rli···~ 2.0

3.0

3.0

13

Pre-injection concentration.

78 & 196

~~~'! 2.0

3.0

Legend

Sample care no.

~ Concentration [ppm)

! ~~. ',0 zp ~ •p :p liP .r:. 1.0 ..., a.. 2.0 Ql

c 3.0

Fig. 1. Sr concentration variation with depth at different locations in fracture A

- 133 -

10

~eiif~;1 2.0

3.0 II

200

2

25

~:~.·. 2.0

3.0 13

o.o~. 1.0

2.0

3.0

Pre-injection concentration.

196 & 79

0.0~ 1.0

z.o 3.0

2.0

3.0

24 2.0

3.0

APPENDIX 10

o. o~s;F'~~Y.ssY.k:~ ! )~ : 1.0

2.0

3.0

~r,&l~ :::;:: 2.0

3.0

28

0.0~ ,,·.''

1.0

2.0

3.0

Legend

Scmp 1 a core no.

~ Concantrotion tppmJ

! o. ol tp zp ~ 4p !;fJ If' .r; 1,0 ..., 0.. 2.0 01

c 3.0

Fig. 2. Cs concentration variation with depth at different locations in fracture A.

- 134 - APPENDIX 10

Legend

Concentration Cppml

'E 0.01 10 <p "" 40 50 e • • • . r • , 1-1

L 1.0

~ 2.0 Ql

Cl 3.0

Cs

Fig. 3. Tracer concentration variation with depth in sample core No. 79 ( pre-injection concentration ) in fracture A.

- 135 -

Legend

Concentration [ppm) ,..., E 0. Ol l 0 20 3Q 40 E 1 I ' I ' 1 ' I ~

1.0 .t.: ~ 2.0 Qj c 3.0

50

APPENDIX 10

Cs

0-0t:s:-~~"""'~~~~~~· 1.0

2.0

3.0

Eu

D. "r""'"~~"""'-·'S."-~'.~'-'%"'-~ . 1. 0

2.0

3.0

Nd

o.or~~~~~,~~~~~~~· ~~0 1. 0

2.0

3.0

Th

u

Fig. 4. Tracer concentration variation with depth in sample core No. 9 in fracture A.

- 136 - APPENDIX 10

Cs

Eu

Nd

Th

u

Legend

~~0 ···~·=-""~" Concentration [ppmJ 2.0

50 3.0~~


- 137 - APPENDIX 10

Cs

Eu

Nd

Th

u

Legend

Concentration [ppmJ

tp O ~Q I ~0 I ~Q I sp


- 138 -

Legend

Concentration CppmJ ,......

~ 0. 01 I

1P 1 2p 1 3p I 4.0 .c 1.0

~ 2.0 01 c 3.0

50

APPENDIX 10

Cs

~~: · .... ~ 3.0

Eu

Nd

Th

u

Fig. 7. Tracer concentration variation with depth in sample core No. 200 from the wall of the injection hole.

' I

40

Sr

Cs

- 139 -

Sr

~~~;o 2.0

3..0

Sr

Pre-injection concentration

50 60

APPENDIX 10

Ce

1.0:e11t;:::~ 2.0

3..0

Legend

Ce

0.0~ 1. 0

2.0

3. 0

Samp 1 e core no.

r""'

i ~0, ~ 1.0

0.. 2.0 Ql

c 3.0

lQ I

ConcQntration tppm)

zp ~ 4p,5p so I

Fig. 8. Sr and Cs concentration variation with depth in fracture B.

- 140 -

54

~:~;::::~""~~ 2.0

3.0

56

~:~ 2.0

3.0 20

APPENDIX 10

26

~:~~,"~' • 3. 0

91

2.0

3.0

60

27

~:~"'~~'I' 2.0-

3.0

44

lZ J' I' 7 8 tiii11JZ15 Ml5l6

Main cores in drilling order

Legend

Pre-injection concentrction. Samp 1 a cora no.

7B & 198 Concentration CppmJ

'.0 zp ~ 'P !p f¥3

Fig. 9. Sr concentration variation with depth in the main cores outside fracture A.

- 141 -

56

Main cores .in drilling order

APPENDIX 10

0.0~ 1.0

z..o 3.0

91

0.0~ 1.0

z..o 3.0

0.0~ 1.0

2.0

3.0

60

0.0~ 1.0

2.0

3.0

44

o.or t.O

2.0

a.o

Legend

PrQ-injQction concentration. Somp 1 C! core! no.

Concontrction tppml 196 '79 tp 2p ~ 4p ~

~~ Z..D

3.0

Fig. 10. Cs concentration variation with depth in the main cores outside fracture A.

- 142 -

APPENDIX 11

Mineral analysis

Figure 1 shows the mineral composition and the Sr and Cs concen

tration variation with depth in a samp 1 e core from the injection hole. A parallel decline in Sr concentration and relative mica content with the depth is observed.

Cs content 50

40

30

Sr content 20 10

0~~--~~--_,~----~r---~~---+,~---i

Mica 10

V&/A K-felspar

R><X>Gi Plagioclase

vZZZI Quarts

20

30

40

50

60

70

eo 90

100

0.35 0. 825 1. 05 1. 275 1. 5 1. 7

Mean qround off depth [mm]

Fig. 1. Mineral composition and Sr and Cs concentration variation with depth in a sample core from the injection hole H2.

This connection between mineral composition and Sr and Cs content is not seen for a number of surface samples. See figure 2A. Sample

core No. 196 comes from the injection hole and No. 131 from the main core No. 6. The rest 191, 192, 193, 197 and 198 comes from the water collecting holes. Figure 2B shows the mineral composition and the measured water flow rates. From figure 2A. and B it seems that the surface concentration of Sr is related to the water flow rate. This makes the interpretation of the mineral composition contra Sr content very complex.

Cs content

Sr content

Mica

~&I

K-felspar

t>OOOOI

Plagioclase

V/Z/l

Cuarts

~

275

250

225

200

175

150

125

100

75

50

25

0

25

50

75

100 "/o

m

196

- 143 -

191 192 193 197 198

Samp 1 e core no.

APPENDIX 11

131

Fig. 2A. Mineral composition and Sr and Cs concentration in surface samples.

20 ml/h

Water flow

Mica

f/0WA K-felspar

tiOO<>a Plagioclase

VZZZJ Quarts

~ 90

100

~ L--------------------------------------------~ 191 192 193 197 198

Samp 1 e core no.

Fig. 28. Mineral composition and measured water flow rate in samples

from water collecting holes.

- 144 - APPENDIX 11

Figure 3 shows the mineral composition of the surface for sample

cores from main cores No. 6 (6:1) and 4 {18:1) and a dry water

collecting hole (G0:1). 11Mix" is a mixcture of crushed Stripa granite.

Only the mixtures have been analysed for Sr and Cs. The second ground

off samples of sample cores GO and 18 were analysed for Cs. The third

ground off samp 1 e of 18 was ana lysed for both Sr and Cs. These resu 1 t s

are all given in the figure.

50~-----------------------------------------~

Cs content 40

Sr content

Remaining incl. mica

w&A K-felspar

~

Plagioclase

vZZZJ Quarts

30

20

10

0~~~~~----~~--~~--L---~~--~--4

10

20

30

40

50

60

70

80

90

100

Sample core no.:depth order

Fig. 3. Mineral composition and Sr and Cs concentration of different

samples.

- 145 -

APPENDIX 12

Pre-injection concentration ( background ).

In the following pages histogramsare presented showing the span of

pre-injection concentration variation for the five different tracer species. Concentrations from samples from the surface and depth are mixed.

Figure 1 shows the results for Sr and Cs from samples from the injection hole only.

Figure 2 shows the results for Sr and Cs from samples from the injection hole and the water collecting holes.

Figure 3 shows the results for Eu, Nd, Th and U from the injection hole and the water collecting holes.

- 146 - APPENDIX 12

Percentage of samples

70

60

so

5 10 15 20 25 30 35 40 45 50 55 60 65 70

Sr ppm


NA 70

60

5 1 0 15 20 25 30 35 40 4 5 50 55 60 65 70

Cs ppm


Sr 70

Cs.AA

5 10 15 20 25 30 35 40 45 50 55 60 65 70

ppm

Fig. 1. Histograms showing the pre-injection concentration variation

of Sr and Cs obtained from samples from the injection hole.

70

60

50

70

60

- 147 - APPENDIX 12


25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400

Sr ppm


5 10 15

Cs ppm

20 25


of Sr and Cs obtained from samples from the injection hole and the water collecting holes.

- 148 - APPENDIX 12

~~p~~r~c~R~nt~o~gEQ~o~f-s~o=mEp~le~s------------------------------~ !~Qr~C~Q~n~to~g~g~o~f-s~o=m~p~le=s--------------------------------, 60

so

50

40

30

20

10

so

30

20

10

0. 2 0. 4 0. 6 o. 8 1. 0 1. 2 1. 4 1. 6 I. 9 2. 0 2. 2 2. 4 2. 6 2. 8 3. 0

Eu ppm

10 20 30 40 50 60 70 80 90 100 110 120 130 140 ISO 160 170 lBO 190 200

Nd ppm

10 15 20 25 30 35 40 50

Th ppm

.P~G~rc~e~n~to~g~g~o~f_s_o_m~p-lG_s ______________________________ __, 60 ...

50

40

30

20

I 0 20 30 40 SO 60 70 80 90 I 00 II 0 120 130 140 I SO 160 170 180 190 200

U ppm


of Eu, Nd, Th and U obtained from the injection hole and the water collecting holes.

- 149 -

APPENDIX 13

Determination of the effective diffus.ivity, De

To determine the effective diffus.ivity five laboratory runs with

iodide were performed.

A hole, with the same dimension as the sample of the rock, was made in

a 120 mm PVC-plate and the sample was fixed in the hole. Two chambers

made of transparent PVC were ~ 1 ued on to the p 1 ate, one to each

side (see Figure 1). One of the chambers was filled with a solution

containing 0.1 mol/J. sodium iodide and the other with 0.1 mol/.R. sodium

nitrate solution. Samples were taken from the chamber containing

sodium nitrate and the concentration of the diffusing iodide was measured. (Skagius 1985). To note is that these samples

had one side cut and the other side was the natura 1 surf ace of the

fracture.

Three of the samples were taken from fracture A within a distance of

0.15 m from the injection hole. The results are very close, ranging

from 1.1 - 1.7•10- 13 m2/s.

Two samples with a distance of 0.1 m were taken from the water collecting hole with very thick fracture filling material, S2-6. They

gave very different results 6.9·10- 12 and 3.6•10- 13 m2/s respective

ly. On the sample giving the high effective diffusivity both sides

were natural and not cut. Part of the edge was broken but to the eye the test set-up seemed to be tight. The results are given in table 1.

- 150 - APPENDIX 13

Table 1. Results from the determination of the effective diffusivity.

Sample No~ Remark

Fracture A 171 1.6•10- 13 Above the injection hole

172 1.7•10- 13 Below the injection hole, opposite 173

172 1.1·1o- 13 Below the injection hole, opposite 172

Water collecting 189 6.9·1o- 12 Thick fracture filling holes S2-6 material. Broken edge.

190 3.6•10- 13 Thick fracture filling material

Hole for sampling of liquid PVC plate

/ Transparent PVC chambers

Fig. 1. Diffusion cell

180

160

140

120

100

80

60

40

20

0

- 151 -

APPENDIX 14

Test of carry-over between samples being ground off

As there is a risk that a con cent ration profile with depth cou 1 d be

obtained due to carry-over from a surface sample with high concentra

tion to the fo 11 owing samples the carry-over have been ex ami ned for

consecutive samples. Figure 1 shows the obtained concentrations for consecutive samples ground with the same diamond coated metal sheet.

The ground of samp 1 es shown are from sever a 1 different sample cores. As can be seen there is no carry-over due to the grinding.

Sr [ mJ

5 10 15 20

Grindinq order

Figure 1. Concentration of successively ground off samples.

- 152 - APPENDIX 14

Concentration profiles obtained due to surface roughness

Figure 2 shows the form that has been used for each sample core taken out from the fracture surface. The unfilled parts of the circles show how much is left of the fracture surface at different depths. As can be seen here there is approximately 2 % left of the surface even at a depth of 1.4 mm.

..\)~,;,~ ~ ... ~\..~\~ 1..1./c;;'

'" ... \V~~\11!\ •. ().\\C> '* X\ t (~ ""~'"-C.... C.

C.c;;. "Eu IJd :,~ I \J

--

I ;~; :-:J-,~ ~\~/() ')..!\ \I .q 'l J.._'S 6~ \<t;L

;.: ~ ~o 0. \D~ ~ ~\ S'.b lDl. ~'-\ 1~

-:>-(-.;

().\\<(:'7 ~ S.'l qD ')._(\ \l.'\ ' ~0

~-'2>t ~.1~ o.qcs-Cl, '2. \

" qL /// 0.\'\S'~ b\ ~-~ be ~~ I,

B'".:'

111 ~

2·b~ :l.~D \.'~..()

'j.,

\Db '/ o. \en_~ 4b l.t> '-\S" 'l.'-1 /q<,

(>. 'l 'i It<:

~ .\(_

~ \.'-\() o.:..o

I . ~~ ~'1 (). \1~~ 1>~ \.\ ~\

~

~ d- .coo '~ \.40

10 ld

~tq "f.~~ :vo~ ~.\S

~ ~'\\\O'l.. ~

'· 6.\'-\10 ~")_ o,'-{, ?..\ ~\ "-\b

(,~-.f

Figure 2. Form used when grinding sample cores.

- 153 - APPENDIX 14

Figure 3a shows the experimentally obtained data. The shaded area is

the background level. The bars in figure 3b are obtained by calculating what the concentration would be if it was only the surface that

contained the sorbed tracer.

Experimental data Without matrix diffusion 300...--------------. 300------------..,

200

100

Figure 3. Experimentally obtained concentrations (a) and calculated

concentrations based on no matrix diffusion (b) at

different depths.

- 155 - APPENDIX 15

Channeling within fracture A

A possibility to detect channeling within a fracture, assuming con

stant sorbing condition over the fracture surface, is to locate

samples with high surface concentration. The parts of the fracture

that have been in contact with the flowing water should have an

elevated concentration of the sorbing species. With a varying natural

content, varying Kd values due to mineral composition and in this

case even leaching before sampling this is very difficult but an

attempt have been made. Figure 1 shows the connected high concentra

tion spots obtained when using Atomic absorbtion analysis, Figure 2

shows the same but for Nutron activation analysis. The two figures

show the same pattern, the flow has been to the right in the fr ac

ture. The arrows in the figures only show the direction of the assumed

channel.

It should be stressed that this is a very vague method to indicate the channelling. Sampling of the complete fracture surface, both sides, may be a way to get more information about the channelling.

This method will be expensive and time consuming.

- 156 - APPENDIX 15

Figure 1. Plausible channels for the flow out from the injection hole based on Atomic absorption.

Figure 2. Plausible channels for the flow out from the injection hole based on Neutron activation.

TECHNICAL REPORT 85-55 - Nagra · RESUME Trois diaclases (fissures) ... Hydraulikversuchen, unter...

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