Site Characterization and Validation—Tracer Migration Experiment in ...

PROJECT 92 03 Site Characterization and Validation — Tracer Migration Experiment in the Validation Drift, Report 2, Part 1: Performed Experiments, Results and Evaluation L. Birgersson, H. Widen, T.Ågren Kemakta Consultants Co. Stockholm, Sweden I. Neretnieks, L. Moreno Department of Chemical Engineering Royal Institute of Technology Stockholm, Sweden January 1992

TECHNICAL REPORT An OECD/NEA International project managed by: SWEDISH NUCLEAR FUEL AND WASTE MANAGEMENT CO Division of Research and Development

Mailing address: Box 5864, S-102 48 Stockholm Telephone: 08-665 28 00

SITE CHARACTERIZATIOH AMD VALIDATION TRACER MIGRATION EXPERIMENT IN THE VALIDATION DRIFT REPORT 2, PART 1: PERFORMED EXPERIMENTS, RESULTS AND EVALUATION

L. Birgersson H. Widen T. Ågren

original contains

i.,.

„

,.

.

o

color illustrations

Kemakta Consultants Co. Stockholm, Sweden I. Neretnieks L. Moreno Department of Chemical Engineering Royal Institute of Technology Stockholm Sweden

January, 1992

This report concerns a study which was conducted for the Stripa Project. The conclusions and viewpoints presented in the report are those of the authors and do not necessarily coincide with those of the client. A list of other reports published in this series is attached at the end of the report. Information on previous reports are available through SKB.

11

ABSTRACT

This report is the second of the two reports describing the Tracer Migration Experiment where water and tracer flow has been monitored in a drift at the 385 m level in the Stripa experimental mine. The Tracer Migration Experiment is one of a large number of experiments performed within the Site Characterization and Validation (SCV) project. The upper part of the 50 m long Validation drift was covered with approximately 150 plastic sheets, in which the emerging water was collected. The water emerging into the lower part of the drift was collected in short boreholes, sumpholes. Six different tracer mixtures were injected at distances between 10 and 25 m from ths drift. The flowrate and tracer monitoring continued for ten months. Tracer breakthrough curves and flowrate distributions were used to study flow paths, velocities, hydraulic conductivities, dispersivities, interaction with the rock matrix and channeling effects within the rock. The present report describes the structure of the observations, ne flowrate measurements and estimated hydraulic con : r.tivities. The main part of this report addresses th nterpretation of the tracer movement in fractured re The tracer movement as measured by the more than 1 N i idividual tracer curves has been analyzed wi .1 the traditional Advection-Dispersion model and a ; jset of the curves with the AdvectionDispersion-^ fusion model. The tracer experiments h a v permitted - -. flow porosity, dispersion and interaction with the r- < matrix to be studied.

Ill

TABLE OF CONTENTS

Page ABSTRACT SUMMARY

ii vii

1

STRUCTURE OF REPORT

1

2

INTRODUCTION

2

2 .1 2.2 2.3 3 3.1 3.2 3.3 3.4

BACKGROUND THE SCV PROJECT AIMS EXPERIMENTAL DESIGN OVERVIEW SELECTION OF INJECTION SECTIONS TRACERS USED PERFORMED EXPERIMENTS

2 3 3 4 4 6 7 9

4 4.1 4 .2 4.3

STRUCTURE OF OBSERVATIONS OVERVIEW WATER FLOWRATF.S TRACER CONCENTRATIONS IN WATER IN THE VALIDATION DRIFT AND THE Tl BOREHOLE ROCK CHARACTERISTICS AND FRACTURE DATA HYDROSTATIC PRESSURES, INJECTION PRESSURES AND FLOWRATES FIELD NOTES SUMMARY OF PERFORMED MEASUREMENTS REFERRING TO LOCATION

11 11 11

FLOWRATE MEASUREMENTS INTRODUCTION INJECTION HOLES VALIDATION DRIFT Introduction RESULTS Overview Flowrate distribution

14 14 14 16 16 18 18 24

4.4 4.5 4.6 4.7

5 5.1 5.2 5.3 5.3.1 5.4 5.4.1 5.4.2

12 12 12 13 13

b 6.1 •5.:. 6.3 6.4 6.4.1 6.4.2 6.4.3 6.5 6.6 7 7.1 7.2 7.3 S 8.1 8.2 8.2.1 5.2.2

TRACER INJECTION AND TRACER B R E A K T H R O U G H D A T A INTRODUCTION TRACER INJECTION WATER COLLECTION COMPILED TRACER BREAKTHROUGH DATA TO VALIDATION DRIFT Overview Recovery distrihiit ion Flowpaths within the H zone DETAILED BREAKTHROUGH CURVE FOR ONE SAMPLING AREA COMPILED TRACER BREAKTHROUGH DATA TO BOREHOLE Tl

27 27 2 930 31 31 39 42 48 50

OUTER DISTURBANCES AND THETR EFFECT ON WATER TNFT.OW AND TRACER MOVEMENT INTRODUCTION VARIATION IN WATER INFLOW RATES VARIATION IN TRACER CONCENTRATIONS

53 53 54 56

DIFFUSION AND SQRPTIQN MEASUREMENTS TN THE LABORATORY OVERVIEW EXPERIMENTAL METHODS AND RESULTS Diffusion Experiment. Sorption Experiment

63 CO 61 61 63

9

SOME CONCEPTS OF WATER FLOW AND TRACER TRANSPORT IN FRACTURED ROCK 9.1 OVERVIEW 9.2 FLOW IN FRACTURES 9.3 SOLUTE TRANSPORT 9.3.1 Dispersion and channeling in fractures, channel networks and fracture networks 9.3.2 Matrix diffusion effects 9.3.3 Sorptinn and other interactions 9.4 BASIC MODELS 9.5 CHANNEL NETWORK MODEL 9.5.1 Flew in individual fractures 9.5.2 Stochastic nature of channels 9.5.3 Solute transport in individual channels 9 . c^ . 5 G-ineration of network 9 ..'3.6 "fluid flow calculations 9.5.7 öolute transport calculations

66 66 67 69 71 76 78 78 81 82 83 83 84 86 87

10 1C . 1 10. L.I 10.1 .2 10.1.3 10.1.4 10.2 10.2.1 10.2.2 10.3 10.3.1 10.3.2 10.3.3 10.3.4 10.3.5 10.3.6 10.3.7 10.4 10.4 .1 10.5 10.5.1 10.5.2 10.5.3 10.5.4 10.5.5 10.5.6 10.5.7 10.6 10.6.1 10.6.2 10.6.3 10.7 10.7 .1 10.7.2 10.7.3 10.7.4

EVALUATION AND INTERPRETATION OF RESULTS MODELS USED FOR FITTING TRACER CURVES Qvervigw Advection-Dispersion model Advect ion—Dispersion—Diffusion, model Accounting for dilution THE FITTING PROCESS

Overview Treatment of iniection curves RESULTS OF MODEL FITTING OF BREAKTHROUGH CURVES Advection—Dispersion model: Individual curves Results using the Advection-Dispersion-Diffusion Model, individual curves Fitting of total breakthrough curves Interpretation of Sr injection Between holes tracer £.£St Multiple pathway fitting Summary of modelling results INFLUENCE ON BREAKTHROUGH CURVES OF MATRIX DIFFUSION EFFECTS

Discussion MATRIX DIFFUSION EFFECTS Overview Flow in fractures with matrix diffusion Theoretical recovery without dispersion Theoretical recovery with dispersion Diffusion into staanant pools of water Evaluation of the early breakthrough of Dy and Ho

Conclusions DETERMINATION OF FLOW POROSITY Methods ar\d. results Specific surface Discussion DETERMINATION OF HYDRAULIC CONDUCTIVITY Overview Hydraulic head measurements Flowrate measurements Results

89 89 89 90 90

91 92 92 93 93 93 105 108 113 114 114 119 121 126 127 127 128 128 129 130 132 136 137 137 139 140 141 141 142 143 144

VI

11

11.8 11.9

INTERPRETATION OF FLOW AND TRANSPORT DATA USING THE CHANNEL NETWORK MODEL OVERVIEW FLOWRATE DISTRIBUTIONS SIMULATION OF FLOWRATES USING THE CHANNEL NETWORK MODEL Comparison of model and experimental results TRACER TRANSPORT SIMULATIONS COMPARISON OF MODEL AND EXPERIMENTAL RESULTS SOME SIMULATIONS ASSUMING A FRACTURE PLANE IN T H E FRACTURE ZONE ESTIMATION OF FLOW POROSITY AND FLOW WETTED SURFACE DISCUSSION AND CONCLUSIONS

12

DISCUSSION AND CONCLUSIONS

190

13

NOTATION

194

14

LITERATURE

196

15

ACKNOWLEDGEMENT

202

11.1 11.2 11.3 11.4 11.5 11.6 11.7

LIST OF ILLUSTRATIONS

APPENDICES 1 2 3 4

INJECTION FLOWRATES MONITORED PRESSURES AS FUNCTION QF TIME RECOVERY OF TRACERS TOTAL BREAKTHROUGH CURVES

STAMP ALONE APPENDICES 5 6

FLQWRATE CURVES FOR INDIVIDUAL SAMPLING AREAS TRACER BREAKTHROUGH CURVES FOR INDIVIDUAL SAMPLING

AREAS. 7 8 9

AD-MODEL FITS TO ALL CURVES FITS QF ALL TOTAL BREAKTHROUGH CURVES FLOWRATE CURVES AND TRACER BREAKTHROUGH CURVES FOR THE BETWEEN HOLE EXPERIMENT

145 145 147 14 9 162 172 176 182 184 185

203

VII

A large scale tracer test, the Tracer Migration Experiment, has been performed as a part of the Site Characterization and Validation (SCV) project in the Stripa experimental mine. The aim of the Tracer Migration Experiment was to study water flow and tracer migration in a fracture zone as well as in the average fractured rock outside the fracture zone and in a broader view to understand and quantify transport processes relevant to the safety of a final reponi1: ^ry for high level radioactive waste in granitic rock. The data obtained have been used for validation/calibration of water flow and tracer transport models. The Validation drift, located 385 m below the surface in water saturated rock, has a natural inflow of wa-er. The water flowrate to the drift was monitored by collecting water in 150 plastic sheets covering thupper part and 10 short boreholes in the lower par' the drift where water visually could be detected. The total water inflow to the 50 m long drift with a surface area of about 450 m2 was close to 600G r.l'h. More than 99 % of the water emerged into the drift in the 6 m long intersection with the fracture zone, rh-- •• zone. The water flow in the H zone was limited to a .•••.•: individual fractures even though the fracture freq:-':. y and hydraulic conductivity were considerably i:u:r-.: compared to the average fractured rock. The water flowrates varied very much between the different sampling areas. 50 % of the total water inflow was found in one sampling area covering 1 m; . The hydraulic conductivity at the intersection with r.hv H zone was found to be 10"9 m/s and 3.5 orders of magnitude lower in the average fractured rock our :;:•:•• ' he H zone. K-Mir boreholes close the Validation drift w r c ;;••:;•• i off except for a total of nine 0.5-2 m socr. ionr, ,i; distances varying from 10 to 25 m from the drift. Th":;e sections were used for injections of six di f f'T^nt" tracer mixtures.

Vill

In or.e experiment, three sealed off borehole secticr.:: located close to the Validation drift were usei f :: tracer monitoring. The tracer breakthrough curves, in all about ibO curves, were analyzed using the Advection-Dispersion model which describe tracer transport. A subset of curves were analyzed using the Advection-DispersionDiffusion model. The fitting of the models to the breakthrough curves gave values of mean residence time from the different injection sections and also information on dispersion. Matrix diffusivities for the tracers were measured in laboratory experiments and used in an attempt to determine values of the average amount of fracture surface in the rock which is ir. contact with the mobile water. The mean residence times were found to vary bet*"-.-^r. 1500 and 4000 hours as averages for the tracers. Considerably shorter as well as longer tirr.es were ro•-::•..i in some of the sampling areas. The flow porosity determined from these data was :;•.::-. i to be 3.5*1O"3 for the tracer injected closest to "r.-drift. The porosity seems to slightly decrease with increasing distance and was 1.6*10"' at the fart h-.v.t injection point. The higher porosity near the iri:: w.*.:; interpreted to be caused by the change of rock :;"re^.-v induced by the presence of the drift. The dispersivir.y was found to be very high for - hv "racers. Typical Peclet numbers of 4 or less wer obtained for most of the tracers. The low value:; n o deemed to be caused by other mechanisms than what ::• usually included in the term hydroaynamic dinper:; i'.;:*.. The main cause seems to be channeling, i.e. the transport of the tracer in channels with differed* transport properties. All tracers injected were found in the Validation drift. The recoveries for the metal tracers var Led between 10 \ and 60 I. Tracers were however r>ti II ••merqing into the Validation drift when the exp--: : ~ SCV block has been extensively investigated using various methods within other projects. For an overview of measurements performed and results obtained, see •. r.-summary report (Olsson, 1992).

14

FLOWRATE MEASUREMENTS

5.1

INTRODUCTION Locations where water inflow rates have been measured within the Tracer Migration Experiment are: - Tracer injection holes Tl and T2 - Validation drift The water inflow rates into the T holes were measured shortly after completed drilling, thereafter the holes were sealed off using compacted bentonite. The water inflow rates into the nine injection sections in the T and C boreholes were measured after the bentonite sealing. The water inflow rates into the Validation drift were continuously monitored in plastic sheets and sump holes during the entire experiment. In the early stages of the SCV Project, before the Validation drift was excavated, seismic and radar measurements indicated the existence of several major fracture zones, among these the H zone intersecting the Validation drift. The next step in the project was to drill the six D boreholes at the exact location where later the drift was to be excavated. The water inflows to D boreholes were almost one order of magnitude higher than those later measured in the drift.

5.2

INJECTION HOLES Four boreholes were used for tracer injection. The two T holes were drilled and monitored for water inflow rates within the Tracer Migration Experiment. The water inflow rates into the C2 and C3 boreholes were measured at an earlier stage of the SCV Project. The water inflow rates were monitored at two occasions in both T holes; (1) March-90, short after drilling and before installation of the bentonite packer system, (2) July90, after installation of the bentonite packer system. The inflow into Tl was as well monitored when used as sampling hole in May/June-91 for tracers injected in borehole T2. For a compilation of monitored water

inflow rates, see Table 5-1. It should re r.o:f.i •':::' each section was monitored for as short tine as ? h •:: : in the measurements done in July-90. These value;; -.7:.then be larger than what would have beer, obtained : r • . longer monitoring time. A compilation ot the result.; from the inflow measurements before the boreholes were sealed off by compacted bentonite and the sections selected for tracer injection is given in Figure 5-1. T1 inflow [mi/h] 4000 -i

v^s Injection i o sections

3000 • 2C00 • 1000 • 1 26

0 •

24

1 28

1 30

1^-1 I s N l 1 r-i | w-i 32 34 36 38

1

40

1

1

42

44

Depth [m]

T2 Inflow (ml h] Injection sections

40003000- • 2000. -

32

30

34

38

36

40

42

44

46

Depth [m]

5-1.

Tl and T2 borehole:;. inflow tor

• wi''"T irorcd

mi j .

tracer

injection.

::.'. l o w r a t ' " " " i n t o h ^ r e h o l ' T " . T ! s r . i " i n 0 . r )m s p c t i o n s . T h " l^n-if h " f " h -

' ] • • • : ' i o n r,e rr, • - r ' i i r . a 1 y f •' f . h o i n f l o w n\r*,-ir,iir»~"rr.^".*.r> «•:•:•":••:•• r ;»»:; i n b o r ^ h o l o T l , :;»*f? F i q ; : r e ^ - l , w r . - - : " :;• h ' h o l e n g t h o f 1 m w n r p . - t . ^ s e n r, i r / 1 " ' w - : . ' • c t i o n s :;••••. • w j r i t o b e i nt.r»r.•".»"• r f « ; r " h ' ;•!••.

T.ti le 5-1.

Compilation of water inflow into the T

roreholes.

[nflow

Section

[ir.I/hj

March-90

July-90

May/June-91

550 13CQ HOC

930 2640 253C

60

2080 1300 3790

10930 11800 1765C

1 2

X.r.er inflow rates above the detection lirr.it, i rr.i r. in, were only found in parts of the holes intersected cy the H zone. The sections of the boreholes located ir. the average fractured rock outside the H zone ail had water inflow rates below the detection limit and could "h-refore not be used as injection sections. It can also be seen in Figure 5-1 that both these boreholes have a few distinct sections with significantly ir.;reased water infiow rate and more or less tight -•.roas between these sections. This observation, :< -'ether with observations in other boreholes intersecting the H zone, indicate that the water : 1 w within the H zone, as well as in the average fracrur^i T^.r-.f., is limited to a few fractures even though rh*"> lecture frequency and hydraulic conductivity is .-. i Tnif icant ly increased compared with the average f r »ctured rock .

I, I DAT I ON DRIFT '- reduction i'^r inflow ^.e-^'iur^ments to the Validation, d :•.•• using thro»? different techniques: (1) pi :'""'fr., ('/) r>T.-p holes and, (3) ventilation

!"h" entire upf>er part of the drift was covered with : i:;f ic :;he"f " whi'h ^rt^'i ,\r, li f

17

emerging water. Water emerging in the lower section of the drift was collected in sump holes that were continuously emptied using pumps. Water emerging in either the plastic sheets in the upper part of the drift or in the sump holes in the lower part was collected in vessels. These vessels were, in cases of high enough water flowrate, emptied two or three times every week to obtain water inflow rates. The drift had to be ventilated, otherwise the Radon content would increase to unacceptable levels. The temperature and humidity in the in- and outgoing ventilation air was measured to give the amount of water "lost" due to ventilation. Most of the water originates from the uncovered lower part of the drift, but the exact locations are not possible to identify. "" 3 circumference of the Validation drift is close to : .. and the upper 5 m were covered with plastic sheets, see Figure 5-2.

lic sheets

1

i 6

7

8

9

1

2

3

••

Figure 5-2.

4

5

31 30 29 28 27 26

Validation drift. Cross section showing area covered with plastic sheets.

The sampling areas were 1 m * 1 m in the 6 m section o the drift intersected by the H zone and 2 m * 1 m in sections outside the H zone. The total number of sampling areas, plastic sheets, in the upper part ot the drift was 145 covering an area of 245 m? and among the.se 30 covering an area of 30 m? were located in the intersection with the H zone.

18

A total of 10 sumpholes were drilled in the lower part of the drift at locations where emerging water was visually detected. A special sampling arrangement was used for sampling area 267 where the water flow was measured in three separate sumpholes; 267:1, 267:2 and 267:3. These three sumpholes had depths of 5, 10 and 30 cm and were during the inflow measurements and tracer monitoring treated as separate sampling areas, but are lumped together in the compilations given in Chapters 5 and 6.

5.4

RESULTS

5.4.1

Overview The total water inflow rate to all sampling areas in the Validation drift was about 6000 ml/h. Altogether 51 sampling areas had measurable inflow rates ranging from 0.01 ml/h to 3000 ml/h. These "wet" areas covered 67 m2 out of a total area of 441 m2 in the drift. More than 99 % of the water emerged into the 6 m long intersection with the H zone located at 24-29 m depth, see Figure 5-3. It should however be noted that a water inflow of about 300 ml/h entering mainly in the lower part of the drift was "lost" due to ventilation and is not included. Approximately 50 % of the total water inflow was located to one single sampling area situated in the lower part of the drift wall. The remaining 50 % of the water inflow was equally distributed between the upper and lower sections of the drift, i.e. between plastic sheets and sumpholes. Most of the water inflow was found in a few sampling areas, as seen in Figure 5-4 .

•T

•Q

006

»•t

0.05V

O)

0,04 \

OJ

c

E

Qj

rr

H-

O 'Si

>-h h-

Q.

s:

0,03-V

o

O

—a ™

O)

o

-.1

-T

Distance trom drift entrance (m)

20

Fraction [%]

80 -

•

•

1

1

•

• *

60 -

•

40 20 -

0 -

1

1

1 3

1 4

1 5

1 6

1 7

1 8

9

10

Number of sampling areas

tigure 5-4.

Fraction of total water inflow as function of number of sampling areas.

Among the many hundreds of fractures seen in the Validation drift, there are two major fractures in the H zone that dominate the water inflow. Sampling areas with high water inflow rates, accounting for more than 9C ". of the total water inflow, are all intersected by ät least one of these fractures. However, these two fractures also intersect areas with low water inflow

The observations above together with Figures 5-3 and 54 illustrate the uneven flow distribution in the Validation drift and also along the trace length of a fracture plane. A question one has to address is if what is observed in a drift is just an effect of changed conditions due to the excavation. It was noted that the water inflow rate was almost one order of magnitude larger to the D boreholes compared to the Validation drift. The D holes were 6 holes on the perimeter of where the drift was later excavated. However, when comparing these two measurements it seems that water is found in the same locations but the magnitude has changed. Comparing the results from the inflow measurements into the T rorehoies with what was observed in the Validation drift, the results are similar in the way that there .-;•".•'.-ms to be a few fractures that carries the largest

21

part of the water. The same result is obtained if other boreholes intersecting the H zone are considered. The sections of these boreholes that intersect the H zone have water inflow rates that vary more than three orders of magnitude and are in some boreholes almost as low as in borehole sections in the average fractured rock outside the H zone (Olsson, 1992). Each borehole may have none, one or a few sections within the H zone with significantly increased water inflow. It appears that the H zone has sections with high permeability as well as low permeability and that the water flow distribution is as uneven in boreholes as in the Validation drift. The water inflow distribution seen in a drift might therefor? ilso be representative for "undisturbed" sections ^n the rock. The magnitude of the water inflow rates are, however, significantly decreased. It is remarkable that the water flow within the fracture zone investigated in the SCV Project, as in the average fractured rock, is confined to a few fractures even though the fracture frequency and total water inflow rate is significantly increased compared to the average fractured rock. There was no indication that the deeper of the three boreholes with depths between 5 and 30 cm in sampling area 267 had higher water inflow rates. Furthermore, the four slots that were between 5 and 30 cm deep and each extending for at least 6 m prevented leakage between the sampling areas so that a larger part of the water was found in the upper part of the drift, but di:i not affect the total inflow to the drift. These observations indicate that the "skin" around the Validation drift extends further out than 30 cm. The total water inflow rate into the Validation drift was almost constant during the 10 month tracer test, see Figure 5-5. The water "lost" in the ventilation air is omitted in the figure, but was found to be 300 ml/h and almost constant with time.

22 Inflow [ml/h] 8000

6000

4000 -

2000 •

0 -t— 3000

4000

Figure 5-5.

5000

6000 7000 Time [h] since Apr 27 1990

8000

9000

10000

Total water inflow rate into Validation drift as function of time.

The increase in inflow rate around 8500 h is caused by an outer disturbance that is discussed in Chapter 7. A

.n example of water inflow rate as function of time for an individual sampling area is given in Figure 5-6. Individual flowrates for each sheet as function of time is given in stand alone Appendix 5. Q 261 25 H • •••

20-

• •• • • • • •• •

••

i 10-1 50I 4000

5000

I 6000

7000

8000

9000

I 10000

Time [hours]

Figure 5-6.

Water inflow rate as function of time for one of the sampling areas in the upper part of the Validation drift.

23

Even though the total inflow rate was constant, individual sampling areas could in some cases have inflow rates varying a factor two or more during the experiment. A corresponding change in one of the nearby sampling areas could in many cases be found, see Figure 5-7. Q 273

140-

A

12010C E,

80-

o

60-

ii.

40-

•

>

#*

•

• • • • ••

20-

*••••* •

0-

I 5000

4000

I

6000 Time [hours]

7000

8000

Q 283 120•

•

100_

80-

~

60-

•

••«•

o

u. 40-

• •

• •

200-

Figure 5-7.

4000

r 5000

6000 Time [hours]

7000

8000

Water inflow rates as function of time for two nearby sampling areas.

24

The fact that the water inflow rate decreases in one sampling area and increases in a nearby area seems to be an effect of local flow redistributions. The most obvious example is the decreasing water inflow rate in sampling areas 282 and 283, while the inflow rate increases in the two nearby areas 272 and 273. These two latter sampling areas are intersected by the fracture with the largest water inflow rate, while areas 282 and 283 are intersected by a smaller fracture that seems to be connected the major fracture intersecting 272 and 282. The notation of the sampling areas is given in Figure 3-3 in Chapter 3.

5.4.2

Flowrate distribution The measurements of flowrate and tracer concentrations in every sampling area and sumphole which carried water made it possible to develop a very detailed description of the flowrate and tracer flow distribution. The flowrate distribution within the 50 m long Validation drift was very uneven depending on the H zone intersecting the drift at 24 to 29 m depth. The water inflow rates into 1 m sections of the drift are given in Figure 5-8. The flowrates into the sections not included in the figure were all orders of magnitude lower and would not have been seen if plotted with the same scale.

Flowrate in section [ml/h] 5000

T

24

25

26

27

28

29

Distance into drift [m]

Figure 5-8.

Flowrate in the part of the Validation drift intersected by the H zone.

25

About 80 % of all water entering the Validation drift is found within a i m section 26 m into the drift. This water originate mainly from one major fracture almost perpendicular to the Validation drift. The number of sampling areas carrying a certain flowrate are shown in Figure 5-9. Note that the flowrate intervals follow a geometric progression with a factor of 2 between them.

Number of sampling areas 10

0.1

Figure 5-9.

6.4 51.2 Flowrate, upper limit [ml/h]

409.6

»1638.4

The distribution of flowrates among the 51 sampling areas with measurable water inflow rate in the Validation drift.

The sampling area with the largest water inflow rate located outside the intersection with the H zone is found in the interval 1.6-3.2 ml/h in Figure 5-9. Sampling areas with larger water inflow rates are all located in the intersection with the H zone. In Figure 5-10 the same data have been plotted to show the flowrate in different flowrate ranges.

26 Flowrate in ranae fml/h] 3500 r 3000 2500 2000 1500 1000 500 0 0.1

Figure 5-10.

0.8

6.4 Flowrate. upper limit [ml/h]

409.6

>1638.4

Sum of the flowrates in different flowrate ranges in the Validation drift .

Even though only a small number of sampling areas have very high water inflow rates, most of the water is found in these areas as illustrated in Figure 5-10.

27

TRACER INJECTION AND TRACER BREAKTHROUGH DATA

6.1

INTRODUCTION Two types of tracer experiments have been performed. In both experiments, the tracer injections took place from 0.5-2 m long borehole sections located between 10 and 25 m from the Validation drift. During the first type of experiment, tracers were injected from 6 different sections and collected in the Validation drift. Out of these 6 sections, 5 were located in the H zone and one in the average fractured rock. During the other type or experiment, tracers were injected in three sections in hole T2 and collected in borehole Tl 10 m away as well as in the Validation drift. A mixture of one dye and one metal was simultaneously injected in each injection section. The locations of the injection sections are illustrated in Figure 6-1 and given in Table 6-1.

H zone

3-D drift

in

iin

•

Validation drift

Sections used for tracer injection.

o Sections used for tracer monitoring.

Figure 6-1.

Location of injection sections.

28

Table 6-1.

Distance to the Validation drift from thin jection sections.

Hole

Section

Distance to Validation drift [m]

~~T1

1 2 3 1 2 3 1 1 2

10 11 15 21 22 25 22 15 18

T2

C2 C3

The distance given in Table 6-1 is the distance fro~ the injection section to the sampling area in the Validation drift where the major amount of the tracers were found. The sections are numbered from the starr of the boreholes. Water samples were collected in the Validation drift during the entire experiment. During the last one ar.J n half month, tracers were injected in borehole T2 ar.d sampled in borehole Tl as well as in the drift. The Tl borehole was at that time kept at zero pressure. The time schedule for the injections and which tracers were used are given in Figure 6-2.

1990 Sep

Oct

1991

Nov Dec : Jan Feb

Mar

Apr

May Jun

T b / Elbenyl

T1:2 T1:3 Re / Rose Bengal

T2:1 T2:2 T2:3

Sr

Gd / Eosin Y

Dy / Phloxine B Eu / Dyasyn Gd / Eosrn Y

Dy / Phloxine B

C2:1

Ho / Uranin

C3:1 C3:2

Eu / Duasyn

— Tracer injection •=» Water sampling Figure 6-2.

Time .schedule for the t r a c e r

injection.1",.

In rid April-Si, two boreholes close to the Validation drift had to be opened for 2 weeks due to instaliatier. of new equipment. This caused a disturbance in water inflow rates and tracer concentrations in the Validation drift which is discussed in Chapter 7. In the following text, breakthrough curves obtained in the drift are only giver, up to the time for the disturbance.

TRACER INJECTION The tracer solutions were continuously injected for time periods of 1 week up to 7 months with a constant flowrates between 2 and 30 ml/h. These injection flowrates are, in most cases, considerable lower thar the natural water inflow rates which reduced the pressure build up due to injection to a minimum. See Table 6-2 for water inflow rates monitored after installation of the bentonite packer systems, inject: flowrates, pressure heads and estimated head increase due to injection.

Table 6-2.

Hole Section

1 2 3 T2

1 2 3

Natural and injection flowrates, natural and induced heads. Flowrates Natural Injected [ml/h] 930 2640 2530

Head Natural Euildup r ~i i i. • • ' >

4.0

17 3 173 172

-5

10930 17.5/30.0 11800 19.0 17650 30.0

174 173 173

-t-: *I +1

1530

15.0

117

63 17

-1.0 2.0

172 173

-3:

30

Figure 6-3 shows the injection flowrate tor or.e c. tr.e injections, all injection flowrates are given in Accendix 1.

Average fiow over 30 min

1000

2000

3000

4000

5000

Time [h] Figure 6-3.

The injection flowrate at injectio: section C3:2.

It can be seen in Figure 6-3 that the injection fiowrate was almost constant for 6.5 months. The pressure in the injection section was slowly increasina with time, but was limited to 35 m of water head. The pressures at the injection sections are giver, in Arnendix 2 .

WATER COLLECTION Water entering the upper as well as the lower part of the drift was sampled for tracers during the 10 month experiment. Water samples were taken every 8:th hour from all sampling areas with high enough water flowrate. Test tube racks were changed every second w>-"k . Each rack centained water samples from up to fiiifferent sarr.pi.ing area:;. During the La.-,?, one -:ir.-: j h 11 f month water samples were also taken from the thr*-. ."••.".•t ions in the Tl borehole. The water samples wore analyzed for dye and metal concentration. The dye concentrations were analyzed at the laboratory in ntripa and the metal concentrations in a remote 1 aboratory.

31

6.4

COMPII.EA

6.4.1

Overview

TRACER BREAKTHROUGH DATA TO VALIDATION DRIFT

An overview of tracer breakthrough is given in the folloving figures. For detailed information of the k-reakthroi;gh curves for each sampling area, see stand alone Appendix 6. The recoveries for the metals were considerably higher than for corresponding dyes. This phenomena is discussed in Section 10.4. Furthermore, dyes in high concentrations may obscure dyes with lower concentrations if the maximum absorbance wavelengths are clo^e. In the following text only the results obtained from the metal complexes are discussed, but it should be noted that the findings are valid even if the dyes are considered. Tracers were found in 41 out of the 51 sampling areas where water was obtained. All sampling areas at the intersection with the H zone carrying water also had measurable amounts of tracers. It was only a few sampling areas in the average fractured rock that did not have any measurable tracer concentrations. See Figure 6-4 for a compilation of where tracers were found in the Validation drift. The H zone intersects the Validation drift between 24 and 29 m depth. A mixture of all six tracers were found in the major part of the sampling areas. The concentrations were in many cases however quite different for the different tracers. Figure 6-5 shows the instantaneous recovery, defined as the maximum mass flow of tracer found at any time divided by the injection mass flow, for all six tracers. The largest instantaneous recoveries are found in different sampling areas for the different tracers even though they in some cases are injected from the same borehole only 5 m apart, see T2:1 and T2:3.

32

CTi

2

Figure 6-4.

(*}

-

•5

(M

Distance from drift entrance (m)

T2:3 Gd

Distance from drift entrance (m)

Figure 6-5b.

Instantaneous recovery for the metal complexes.

35

C3:1 Ho

25 6

Recovery upper limit, per cent of injected mass

Figure 6-9.

Histogram over the recovery of Dy (C2:l) in different mass flow rate ranges. 38 sampling areas carried this tracer in measurable quantities.

40

Per cent recovery in recovery range

10 -r

•+•

0.1

0.2

0.4

0.8

1.6

3.2

6>

12.8

^

•+•

25.6

>25.6

Recovery upper limit, per cent of injected mass

Figure 6-10.

Histogram over the recovery of Eu (C3:2) in different mass flow rate ranges. 38 sampling areas carried this tracer in measurable quantities.

Per cent recovery in recovery range

30 -r

20 -

10 -

-J

•+•

0.4

0.8

1.6

3.2

6.4

12.8

25.6

>25.6

Recovery upper limit, per cent of injected mass

Figure 6-11.

Histogram over the recovery of Gd (T2:3) in different mass flow rate ranges. 38 sampling areas carried this tracer in measurable quantities.

41

Per cent recovery in recovery range 20 T

1 5 ••

105 ..

0.4

0.1

0.8

1.6

3.2

6.4

12.8

25.6

>25.6

Recovery upper limit, per cent of injected mass

Figure 6-12.

Histogram over the recovery of Ho (C3:l) in different mass flow rate ranges. 38 sampling areas carried this tracer in measurable quant it ies.

Per cent recovery in recovery range 40 T 30 20 10 21

3

3

1

0.1

0.2

0.4

0.8

1.6

3.2

6.4

12.8

25.6

>25.6

Recovery upper limit, per cent of injected mass

Figure 6-13.

Histogram over the recovery of Re (T2:l) in different mass flow rate ranges. 38 sampling areas carried this tracer in measurable quantities.

42

Per cent recovery in recovery range 20 T

0.1

0.4

0.8

1.6

32

6.4

12.8

25.6

>25.6

Recovery upper limit, per cent of injected mass

Figure 6-14.

Histogram over the recovery of Tb (Tl:2) in different mass flow rate ranges. 38 sampling areas carried this tracer in measurable quantities.

It can be seen in Figures 6-9 to 6-14 that one or a few sampling areas carry the most tracers even though measurable concentrations were found in 38 sampling areas. This illustrate the uneven tracer distribution found in the drift and that a few flowpaths, channels, contribute to almost the entire tracer transport.

6.4.3

Flowpaths within the H zone The patterns for most of the mass flow rates illustrated in Figure 6-6 indicate that some of the tracers have emerged into the Validation drift through the same flowpath(s). This observation is further discussed in this section. The patterns obtained when mass flow rates are considered depend on the tracer concentrations as well as the water flowrates to the sampling areas. A large mass flow rate can be obtained for a sampling area with low concentration if the water flowrate is large enough. It could be that differences in water inflow rates to some extent have caused the observed mass flow patterns. Some measure is needed to compare the

43

dilution in different sampling areas and for different, tracers. The ratio between accumulated mass ar.d water flowrate was chosen. This number gives a weighted average concentration in the sampling area. To normalize this number, it was divided by the ratio for a reference sampling area, chosen as area 269, where the largest mass flow rate for some of the tracers were found, see Equation 6-1.

Q

sampling area

Q

reference area

The number obtained from Equation 6-1 will be 1 fcr all sampling areas with the same dilution, "average concentration", as the chosen reference area and less than 1 if more diluted. Figure 6-15 shows the r.uriers obtained for the different tracers at different locations in the Validation drift. Tracers were found in more sampling areas than indicated in the figures, but numbers below 0.1 have been emitted.

Dy(C2:1) !

Sump holes

0.4

0.6; 0.4:

|

_l 7 " 8 ij 9

j

j

i

1

:

i

:

0.3 0.3 0.6 0 7 0.4 03

02

Plastic sheets

1 ;o.8

02 02

0.3 j 0-3 0 , O3

i o.i i

0.1

0.1

io.i 0.1

0.1 0.1 \

Sump holes

i

'•

•

0.1 j

0.4j

i

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Ho(C3:1) Sump holes

i

i 7 8 1

0.1

Plastic sheets

03

2.8

0.3

0 7 0.1 0.7 0.1 0.1 0.1

0.1

0.1 0.1

Sump holes

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Eu (C3:2) Sump holes

0.1

i

I ! I

i

•

i

Plastic sheets

_..

1

I

03

;1|3.O;

0.3

,1.0! 0.1 0.7

j

Sump : holes :_...

'

I

0.1.0.4! 0.3

:

0.3 0.2

i

^

02

j

1

! 1

[ ;

•

I

'

i

i

.

!

I

;

!

!

i

.

i

1

X

8 9 1 2 3 4 5

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Figure 6-15a. "Average concentrations" for the different tracers normalized to "ar-r1. ir. area 269.

45

Re (T2:1) Sump holes

0.1

OS

3.0

o.:

0.1

Plastic sheets

0.1

1

0.3 0.4

0.9

0.1 25 2.6 1.7 0.4 2.0 29

1.4

0.1 1.8 3.5

4

02

0.1

0.2

7 \A

2.3

Sump holes

0.3

6 7 8 9 1 2 3 4 5

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39

02

Sump holes

8

0.1

Plastic sheets

0.1

1

2.7

0.4

0.7 0.1 0.7 0.1 0.1 0.1

0.3

2 3

0.1

0.1 0.1

Sump holes 23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Gd (T2:3) 02

Sump holes Plastic sheets

0.1

1

27

0.1 11 0.6 1.0 0.2 0.6 0.5 0.5 0.6

Sump holes

0.1

05 0.5 0.5

0.1

0.1 0.1

0.3 0.4

0.3 0.1

6 7 8 9 1 2 3 4 5

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Figure 6-15b. "Average concentrations" for the different tracers normalized to sampling area 269.

46

The numbers for Eu, Ho and Tb in Figure 6-15 are almost identical. These tracers were injected in two sections 6 m apart in the C3 borehole and the Tl:2 section. It seems that these three t.acers have been transported to the Validation drift through the same major flowpath(s), channel(s). Gd, T2:3, has similar numbers as the above three tracers in most of the sampling areas, but is found in a larger number of areas, some even outside the intersection with the H zone. Dy, C2:l, and Re, T2:l, both have patterns showing that these tracers have migrated in other flowpath systems than the previously mentioned tracers. Dy was the tracer injected to the side and below the Validation drift and is found in quite different sampling areas compared to the other tracers. Re is found in about the same areas as Gd but with significant different numbers. It seems that there are three distinct patterns: (1) Dy, (2) Re and (3) Eu/Ho/Tb. Gd has a pattern that reminds of that for Eu/Ho/Tb but is, as Re, found in a larger number of sampling areas. Figure 6-16 gives the ratio between Gd, T2:3, and Eu, C3:l, still with sampling area 269 as reference. The numbers then obtained are close to 1 in the section of the drift were both tracers have high "average concentrations". This is seen in Figure 6-16 where the sampling areas with a ratio less than 2.5 are shaded. The areas outside the shaded areas have ratios up to almost 300 indicating that a fraction of the Gd tracer have migrated to the Validation drift within flowpaths, channels, not used for the Eu/Ho/Tb transport.

47

Gd/Eu (T2:3/C3:2) Sump holes

276

48 95

38

6.8

46

Plastic sheets

Sump holes

H

22 13 11 3L4 35

ts\ 11 1 OS

2.9

63

1 3 1 * 2J3

24 I S 2,1

25

187 17 32

7.1 104

2.5

8.0

46 243

157

6 7 8 9 1 2 3 4 5

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Figure 6-16. Gd/Eu "average concentration" ratio normalized to sampling area 2 69.

If the ratio between Gd, T2:3, and Re, T2:l, is considered, see Figure 6-17, and the same areas as in Figure 6-16 are shaded it seems that the areas not shaded have almost the same ratio, 0.3. The shaded areas have ratios varying from 0.2 up to 1.3.

Gd/Re(T2:3/T2:1) Sump holes

0.3

0.3 0.1

0.3

0.5

• < 2 5 in Gd/Eu

0.5 0.4 0.9 0.2 0J5

Plastic sheets

Sump holes

1.3 03

1

0J

0.8 0.4 02

ae

0.3

0.5

JO.4 03 02

0.3

i 0.3 03 0.2

02 0.3

0.3

0.3 0.3

0.3

0.1 0.3

0.2

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Figure 6-17. Gd/Rs "average concentration" ratio normalized to sampling area 269.

6 7 8 9 1 2 3 4 5

48

The uniform Gd/Re-ratio in the unshaded areas indicate that these two tracers have been mixed a distance from the drift and been transported to these areas in the drift in the same flowpath(s). The slightly odd "average concentration" pattern for Gd can, based on the above discussion, be explained if the injected Gd has divided into two major flowpaths, o n e which coincides with the three tracers injected in C3 and T l , Eu/Ho/Tb, and the other with R e . The above results and figures can be interpreted as that the transport of tracers from the six injection sections to the vicinity of the Validation drift have occurred in three major separate flowpaths. The major flowpaths, channels, important for the tracer transport should then be: (1) from the C2 hole, Dy; (2) from the C3 and Tl holes, Eu/Ho/Tb, located 10-15 m above the drift and; (3) from the T2:1 injection section, R e . The transport of Gd, T 2 : 3 , seems to be a combination of flowpaths (2) and ( 3 ) . The flowpaths seems to spread out over a large area close to the drift, which might be an effect of reduced rock stresses due to the excavation.

6.5

DETAILED BREAKTHROUGH CURVE FOR ONE SAMPLING AREA The detailed breakthrough curve for one of the sampling areas in the H zone is shown in Figure 6-18. C/Co'10C0 16 T

O

1000

2000

3000

4000

5000

6000

Timo(h]

Figure 6-18.

Detailed breakthrough curve for one sampling area before data processing.

49

Obvious erratic concentration analysis had to be eliminated in the unprocessed breakthrough curve given in Figure 6-18. Due to problems with the metal analysis almost 25 % of the concentration values had to be rejected. Figure 6-19 shows the breakthrough curve after elimination of these erratic points.

C/Co*1000 16 14 12 -

10 -

•"

• •

•

_

•• • ••

•

:•

o O

1000

2000

3000

4000

5000

6000

Time [h]

Figure 6-19.

Breakthrough curve after elimination of erratic tracer analysis.

The processed curve, illustrated in .- are 6-19, still had some minor variations in tracer concentration that can be explained by noise in the analysis and/or variation in the water inflow rates. The breakthrough curves given in stand alone Appendix 6 that have been used in the fitting processes to various models are in the same way as the curve given in Figure 6-19 only corrected for erratic analysis. The breakthrough curves have not been smoothed in any way before the fitting process. The breakthrough curves for the dyes were much smoother and only a small number of concentration values were rejected due to erratic analysis.

50

6.6

COMPILED TRACER BREAKTHROUGH DATA TO BOREHOLE Tl The time available for the tracer test between the T2 and Tl boreholes was only 1.5 months. The three sections in borehole Tl were opened about 2 weeks prior to the start of tracer injections in T2. The sections in Tl were kept open during the entire in between hole test. The water inflow rates into two of the sections in the Tl borehole were found to have decreased considerably compared with measurement? performed approximately 8 months earlier. Both these sections are intersected by fractures almost parallel to the borehole. It might be that the competed bentonite used for sealing of the injection sections also had sealed these fractures and thereby reduced the water inflow. The water inflow rates found were; Tl:l 60 ml/h, Tl:2 60 ml/h, and Tl:3 1000 ml/h. Large amounts of tracers injected earlier in the T and C boreholes were found when opening the sections in Tl . However, after two weeks these concentrations had decreased to acceptable levels, the pressures in adjacent boreholes and flowrates into Tl had stabilized, so the tracer injections in T2 could be started. Tracers were continuously injected in the three sections in borehole T2 for 9 days and monitored for in the Tl sections as well as in the Validation drift. Figure 6-20 shows the total breakthrough of the three tracers to the sections in the Tl borehole.

51 Dy i OH T2:1 0 8-

o o

0.6-

0 4-

.••+++:-

0.2-

+++•• '••••+•+..

0.0-200

200

400

I 6C0

T 800

Tim» (hj

Eu 1 OH T2:2 0.8-

o

0 6-

0 4-

02-

0.0•200

200

r

400

600

800

400

600

800

Time (h)

Gd 1 OH T2:3

08-

0.6-

0.4-

02-

0.0

T

200

200 Time |h]

Figure 6-20.

Total breakthrough curves in the Tl borehole. Note that different scales are used.

52

The breakthrough curves illustrated in Figure 6-20 are not corrected for the decreasing background concentration of the tracers. This correction was done before fitting the curves to the models by fitting the first part of the breakthrough curve to an exponential function and reducing the curve by the obtained function. The breakthrough curves for the individual sampling sections in Tl are given in stand alone Appendix 9. The shapes of the breakthrough curves are strange in that way that the concentration increases rapidly, but decreases very slowly after completed tracer injection. Therefore, in order to fit the curves to theoretical models only the part of the curve extending up to about 50 hours after the peak concentration was used.

53

OUTER DISTURBANCES AND THEIR EFFECT ON WATER INFLOW AND TRACER MOVEMENT

7.1

INTRODUCTION It was attempted to avoid outer disturbances in the SCV block during the entire experimental time. The only major disturbance during the 10 month experiment was when boreholes Cl and Wl had to be opened due to reinstallation of equipment, see Figure 7-1.

1990 Sep

Oct

Nov

1991 Dec I Jan

Feb

Mar

Apr

May Jun

Tb / Elbenyl

T1:2 T1:3 Re / Rose Bengal

T2:1 T2:2 T2:3

Sr

Gd / Eosin Y

Dy / Ph B Eu/Duasyr Gd / Eosin Y

Dy / Phloxine B

C2:1

Ho / Uranin

C3:1 C3:2

Eu / Duasyn

Tracer injection

Figure 7-1.

a

Water sampling

Time schedule for the tracer injections and the opening of boreholes Cl and Wl.

The Cl and Wl boreholes were opened in mid April and were kept open until the beginning of May which was about 400 hours. Both these boreholes have large water inflow rates at the intersection with the H zone. The opening of these holes caused significant changes in water and tracer inflow rates in the Validation drift.

54

7.2

VARIATION IN WATER INFLOW RATES The total water inflow into the Validation drift was almost constant for the first 7.5 months of the experiment, but was changed when boreholes Cl and Wl were opened, see Figure 7-2.

Inflow [ml/h] Cl and Wl open 8000 -g

6000 •

•

•

•

9000

10000

• •

.

"

-

•

•

-

.

4000 •

2000 .

0 3000

1 4000

-H 5000

1

1

1

6000

7000

8000

—1

1

Time [h] since Apr 271990

Figure 7-2.

Total water inflow rate into Validation drift as function of time.

Figure 7-2 illustrated the mean values for the water inflow rate every 500 h. The water inflow rate decreased when the boreholes were kept open. This is however not surprising considering the large inflow rates into both Cl and Wl. When these boreholes later were closed, after reinstallation of the equipment, the inflow rate into the Validation drift increased to a higher level than before the disturbance! The flowrate for an individual sampling area is shown in Figure 7-3.

55 Q 261 25•

•••

20-

1" 15-

f -o-

.•***•

.••••••/*

50-

I 4000

I 5000

I 6000

I 7000

I 8000

I 9000

l 10000

Time [hours]

Figure 7-3.

Water inflow rate into one individual sampling area.

The change in water inflow rates were quite different in the individual sampling areas as illustrated in

Figure Sump holes Plastic sheets

Sump holes

-

Changes in inflow at 8500 h 50

20

0

20

50 50 40

?

?

0

0

50

0

?

8 ?

0 0

60 0

0

0

0

0

0

0

?

0

0

0

?

?

0

0 0

0

0

0 50

10

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Figure

7-4.

Change in water inflow rate after installation of equipment in Cl and Wl.

Increase in water inflow rate is found within the section of the two major fracture planes where the tracer injected in injection section C2:1 was found. Other sections of these fractures and the rest of the sampling areas do not have any significant change in the water inflow due to the reinstallation of the equipment in Cl and Wl.

56

7.3

VARIATION IN TRACER CONCENTRATIONS The tracer concentration changed drastically in sor-.e of the sampling areas due to the disturbance. In most sampling areas, the tracer concentrations were significantly larger after the disturbance than before. In some sampling areas this effect seems to be temporary and the concentration changes back to what seems to be normal after a few hundreds hours, while the concentration change seems to be permanent in other sampling areas. These permanent changes indicate redirection of flow paths due to the disturbance. There is also a significant difference between the tracers. Some show large changes in concentration, while other show only minor changes. Some tracers also show a permanent change in a significant number of sampling areas . For a compilation of the changes in tracer concentration due to the disturbance, see Figure 7-5.

57 [ j -prmjnw Q .umponry

C2:1 Sump holes

•GO

.100

»too

•CD

.100 •100 *SB

!6 7 8 9 1 2 3 4

T

•MB

Plastic sheets

Sump holes

—

»too

100

23 24 25 26 2728 29 30 31 32/33 34/35 36/37 38/39

a•

pwmvwnt

-twnporaiy

Sump holes JO0

Plastic sheets

0

7

I

»50

8 9 1 2 f 3 1 f4

i

.100 *30D -SO

7

7

.100

-3D -60

.ISO

-as

-10

.10

-a

-25

0

0 7 0

7

Sump holes

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 -permanent

C3:2

-temporary

Sump holes .200

Plastic sheets

8 9

0 -25 -25 0

0

-50

-as

7

I I

Sump holes

t I. ._. 23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39

Figure 7-5a.

I

Change in tracer concentrations due to reinstallation of equipment in Cl and Wl

58 j_J .parmanM

T12

6 7 8 9 1 2 3 4 5

Sump holes .an

Plastic sheets

0

7

«aoo -75

7

-«

?

•100

.to

•ISO -Ct - S

-69 -60

Sump holes

7

0

i

23 24 2526 2728 29 30 3132/33 34/35 36/37 38/39 12:1

|

j •parmananl

•

-temporary

I

Sump holes

i 1

Plastic sheets

8

i 7

0

0

0

0

0

0

'ion 0

0

0

.ISO

Sump holes

-10

.100 -10

7 0

0

-10

i 23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 0

[H -pmnwwii [ j -Mmpora/y

72:3

j

Sump holes •500

Plastic sheets

7

.100 0

.100 •600 -60 •100

-as

-25

7

0

• ISO -25 -25

-5

•100C -25 - K

0

7 i

0

0

^»

Sump holes

lo'—

6 7 8 9 1 2 3 4 5

23 24 25 26 27 28 29 30 31 32/33 34/35 36/37 38/39 Figure 7-5b.

Change in t r a c e r concentrations duo to rei.nst.al lat ion of equipment, in Cl arv.i W:

59

The responses due to the disturbance are very similar for the tracers injected in sections: Tl:2, C3:l, C3:2 and T2:3, where the concentrations decrease and increase in almost the same number of sampling areas and about one third of the responses seems to be permanent. The tracer injec;. ^a in C2:1 seems to have a permanent increase in the concentration in almost every sampling area. The tracer injected in section T2:1 has temporary changes and is not affected at all in a large number of sampling areas. There seems to be three groups of responses due to the disturbance. These groups are identical to tho-e found in Chapter 6 when the major part of the mass flowrates were studied.

60

DIFFUSION AND SQRPTIQN MEASUREMENTS IN THE LABORATORY

OVERVIEW Diffusion of tracers into the rock matrix will withdraw part of the tracers from the mobile water and thus change the shape of the breakthrough curve. Earlier experiments (Skagius and Neretnieks, 198 6a) show that tracers, such as Iodide, Uranin and Chrome-EDTA, diffuse into the rock matrix. The matrix in crystalline rocks is thus porous and typical values for the porosity in crystalline rocks are found to be between 0.06 and 1 %. The dyes had previously been examined for sorption on granite during the 3-D Migration Experiment (Abelin et al., 1987) and were found to be nonsorbing for a test period of 2 years, but the design of the sorption experiment made it difficult to detect weak sorption due to the small amount of crushed rock compared to the water volume. The Me-DTPA complexes used in the Tracer Migration Experiment had not been examined earlier. The metals should, however, theoretically form strong nonsorbing complexes with DTPA. Field experiments in the Finnsjön Area with Gd-DTPA and ReO 4 ~ have given very encouraging results indicating that they are nonsorbing (Gustafsson et al., 1989). It was noticed soon after the first tracer arrival that the dyes emerged in lower relative concentrations compared to the metal complexes. The reason for this could be larger interaction with the rock matrix due to sorption and/or diffusion. A series of laboratory experiments were started in order to obtain values of sorption and effective diffusivity for all tracers used. For more detailed information about methods, theory and results of the laboratory experiments, see Report 1 of the Tracer Migration Experiment.

61

o. .2.1

EXPERIMENTAL METHODS AND RESULTS Diffusion Experiment The technique and equipment used in the diffusion experiment was similar to the one used in the 3-D Migration Experiment (Abelin et al., 1987) and by Skagius and Neretnieks (1986a) . Pieces of red granite from the H zone with a diameter of 42 mm and a thickness of 10 mm were taken from the drill cores from the Tl and T2 boreholes and glued into a 45 mm hole in a PVC plate. The plate was placed between two vessels covering the rock sample. The vessels were glued onto the PVC plate and filled with liquid. One vessel was filled with a concentrated tracer solution and the other with water and Sodium Nitrate. The amount of Sodium Nitrate added made the ionic strength identical in both vessels. Samples of 10 to 20 ml were taken from the low concentration side at regular intervals and replaced with the same amount of water and Sodium Nitrate in order to keep the volume and ionic strength intact. The experiment continued for 4 months and during this time the concentration on the high concentration side was virtually unchanged. Figure 8-1 shows the equipment used in the measurements. Figure 82 shows the breakthrough curves from diffusion experiment number 1 in which the amounts of metal tracers that have diffused through the rock slab is given as a function of time. A straight line is drawn indicating an effective diffusivity of 2*10"i3 m 2 /s. Table 8-1 gives the compiled results. Diffusion cell

PVC plate

Hole for sampling of liquid

X Rock sample PVC chambers

Figure 8-1.

Principle of layout of diffusion cell used in matrix diffusion measurements

62

|Effective diffusivity -

120

2E-13J

tal.

100