APPENDIX A Hydrogeologic Data Interpretation and Modelling Methods and Tools

276 Pages·2012·6.75 MB·English

Interpretation and Modelling
  Approaches and Tools:
Hydrogeology
APPENDIX A
Hydrogeologic Data Interpretation and Modelling
Methods and Tools: Finland
Interpretation and Modelling
  Approaches and Tools:
Hydrogeology

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Interpretation and Modelling
  Approaches and Tools:
Hydrogeology
Contents
1.0  Interpretation Methods and Tools .......................................................................................... A-1 
1.1  Brief Overview of the Site Location and Geologic Setting .............................................. A-1 
1.2  Summary of the Characterization activities .................................................................... A-2 
1.3  Watershed Data Interpretation and Tools ....................................................................... A-4 
1.3.1  Precipitation Data Interpretation Method and Tools ............................................. A-4 
1.3.2  Evapotranspiration Data Interpretation Method and Tools ................................... A-4 
1.3.3  Recharge Interpretation Method and Tools .......................................................... A-4 
1.3.4  Groundwater Baseflow Interpretation Method and Tools ..................................... A-4 
1.3.5  Groundwater Levels Interpretation Method and Tools ......................................... A-5 
1.3.6  Trend Analysis (Precipitation and Groundwater Levels) Interpretation
Method and Tools ................................................................................................ A-6 
1.4  Hydrogeologic System Characterization Methods and Tools ......................................... A-7 
1.4.1  Porosity and Permeability Laboratory Data Interpretation Methods ..................... A-7 
1.4.2  Borehole Fluid Density Surveys - Interpretation Method and Tools ................... A-10 
1.4.3  Borehole Fluid Logging Surveys - Interpretation Method and Tools .................. A-13 
1.4.4  Fracture Aperture Measurement - Interpretation Method and Tools .................. A-14 
1.4.5  Aquifer Properties - Single Well Tests Interpretation Method and Tools ............ A-14 
1.4.6  Aquifer Properties - Multi-Well Tests Interpretation Method and Tools ............. A-17 
2.0  Modelling Methods and Tools .............................................................................................. A-19 
2.1  Watershed System Modelling Methods and Tools ....................................................... A-19 
2.1.1  Watershed Data Processing Software ............................................................... A-19 
2.1.2  Watershed Modelling Methods & Software ........................................................ A-19 
2.1.2.1  Modelling approach and objectives ..................................................... A-19 
2.1.2.2  Presentation of the code ...................................................................... A-20 
2.1.2.3  Spatial and Temporal Discretization .................................................... A-20 
2.1.2.4  Calibration............................................................................................ A-21 
2.1.2.5  Uncertainty and Sensitivity Analyses ................................................... A-21 
2.1.3  Watershed Visualization Tools ........................................................................... A-21 
2.2  Hydrogeologic System Modelling Methods and Tools .................................................. A-22 
2.2.1  Hydrogeologic Modelling Method ....................................................................... A-22 
2.2.1.1  Development of Spatial Variability of Input Parameters ...................... A-22 
2.2.1.2  Upscaling Method ................................................................................ A-25 
2.2.1.3  Dimensionality of Model ....................................................................... A-25 
2.2.1.4  Spatial Heterogeneity and Driving Forces ........................................... A-27 
2.2.1.5  Calibration Techniques ........................................................................ A-27 
2.2.1.6  Uncertainty Analysis Technique .......................................................... A-28 
2.2.2  Hydrogeologic Data Processing Software .......................................................... A-28 
2.2.3  Hydrogeologic Modelling Software ..................................................................... A-28 
2.2.4  Hydrogeologic Visualization Tools .................................................................... A-28 
3.0  References ........................................................................................................................... A-29 

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List of Figures
Figure 1-1  Location of the four sites investigated by Posiva in Finland and close-up on
the Olkiluoto Island considered for hosting the final deep repository. ..................... A-1 
Figure 1-2  Changes in groundwater table levels and corresponding changes in
measured heads by depth in two drill holes (OL-KR12 and OL-KR29) in
spring and summer 2006. Factors represent the portion of magnitude of
surface change by depth (Ahokas et al., 2008). ...................................................... A-6 
Figure 1-3  Baseline heads produced by Ahokas et al. (2008) for different boreholes. ............. A-7 
Figure 1-4  Observations and long-term means (straight lines) of groundwater table
levels observed on reference drillholes (Ahokas et al., 2008). ................................ A-8 
Figure 1-5  Example of autoradiograph (top) and porosity histogram (bottom) of a core
sample tested with the 14C-PMMA Method. Total porosity of 2.9 % was
determined (Lindberg et al., 2010). ......................................................................... A-9 
Figure 1-6  Temperature of water in six different boreholes and the linear mean used in
density correction (Ahokas et al., 2008). ............................................................... A-12 
Figure 1-7  The down-hole equipment of the Difference Flow Meter (DIFF) developed
by Posiva (Rouhiainen 2000). ............................................................................... A-13 
Figure 1-8  Example of hydraulic connections between boreholes based on pumping
tests and cases selected by Vaittinen et al. (2008). The connections
visualized as red tubes are assessed more certain than green tubes. The
colour of the sections refers to different hydrogeological structures. .................... A-18 
Figure 2-1  Geometry and location of the 10 planar hydrogeological zones (HZ) over
the Olkiluoto Island considered in the site-scale hydrogeological model
(Löfman et al., 2009). The extension of the model volume corresponds to
the black solid lines. .............................................................................................. A-23 
Figure 2-2  Schematic functioning of the numerical algorithm used for spatially varying
infiltration (Löfman et al., 2009). ............................................................................ A-24 
Figure 2-3  Simulated flow paths from the potential repository rock block to the surface
considering the flow model that includes the hydrogeological zones (HZ).
The paths have been calculated from the equivalent continuum porous
medium (EPM) model applying the hydraulic conductivities based on the
geometric means of the measured transmissivities (top) and upscaling from
the discrete fracture network (DFN) model (bottom) (Löfman et al., 2009). .......... A-26 
List of Tables
Table 1-1  Summary of the main characterization activities performed over the period
2006-2008 at Olkiluoto, which have contributed to the Hydrogeology Site
Descriptive Modelling of 2009 (according to Posiva Oy, 2009). .............................. A-3 
Table 1-2  Comparison of salinity measurement methods used in the 3D salinity model
of Olkiluoto according to Palmén et al. (2004). ..................................................... A-11 
Table 2-1  Summary of the Boundary Conditions of the site-scale groundwater model
(Löfman et al., 2009). ............................................................................................ A-24 

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1.0 Interpretation Methods and Tools
1.1 Brief Overview of the Site Location and Geologic Setting
Radioactive waste from nuclear power plants is managed in Finland by Posiva, an organization
responsible for research into a final spent nuclear fuel disposal and for the construction, operation,
eventual backfilling and closure of this final disposal facility.
As part of the Finish programme for geological disposal of spent nuclear fuel, detailed site
investigations and an environmental impact assessment procedure were carried out for four sites
from 1993 to 2000: Romuvaara in Kuhmo, Kivetty in Äänekoski, Olkiluoto in Eurajoki, and
Hästholmen in Loviisa (Figure 1-1). The Olkiluoto Island in Eurajoki was found to have a larger area
reserved for the repository. Furthermore, the largest portion of the spent nuclear fuel was already
on the island. Consequently, Posiva proposed Olkiluoto in Eurajoki as the site for hosting the final
repository. The KBS-3 concept developed by SKB in Sweden (Banwart et al., 1997, Hedin et al.,
2001) was selected as the preferred waste disposal concept for the disposal of spent fuel.
Olkiluoto is a large island, about 10 km2 in size, located on the Baltic Sea coast and separated from
the mainland by a narrow strait (Figure 1-1). The Western part of the island already hosts the
Olkiluoto nuclear power plant, with two reactors in operation, a third one under construction and a
forth in the planning stage, as well as a repository for low and intermediate waste.
The final deep repository for spent fuel will be constructed in the central and eastern part of the
island at a depth of between 400m and 600 m in the crystalline bedrock. An underground rock
characterization facility, the ONKALO, has been constructed since 2004 in the central part of the
island. This facility has been used for research and to develop excavation and final disposal
techniques in realistic conditions.

Figure 1-1 Location of the four sites investigated by Posiva in Finland and close-up on the
Olkiluoto Island considered for hosting the final deep repository.
The crystalline bedrock of Olkiluoto is part of the Precambrian Fennoscandian Shield and comprises
metamorphic and igneous rocks developed between 1930 Ma and 1800 Ma which have been
subjected to brittle and ductile deformations as well as hydrothermal alteration.
The dominant rock types at Olkiluoto are divided into four major classes crossed-cut by dykes:

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 Migmatitic gneisses (64% of the bedrock volume);
 Tonalitic-granodioritic-granitic gneisses (8% of the bedrock volume);
 Mica gneisses, quartz gneisses and mafic gneisses (8% of the bedrock volume); and
 Pegmatitic granites (20% of the bedrock volume).
Since the opening of the North Atlantic, the bedrock has been subjected to tectonic uplift of up to
1-2 km in the Palaeogene and Neogene, which was amplified by isostatic rebound in response to
the glaciation during Late Pliocene and Pleistocene. The bedrock was eroded almost to its present
level prior to the beginning of the Cambrian (about 600 million years ago). Due to erosion and
continental conditions, it is almost totally lacking in sedimentary rocks younger than the
Precambrian.
Three distinct tectonic domains, which are split up by two main shear zones, have been identified on
the Olkiluoto Island and characterized by a relative intensity of deformation. Gently South-East-
dipping fault zones were found to be the main hydrogeological features of the site (Posiva Oy 2009).
1.2 Summary of the Characterization activities
Site characterisation activities at Olkiluoto have been taking place for over 20 years by means of
ground- and air-based methods completed by an extensive programme of shallow and deep
(300 - 1000 m) boreholes.
Since the late 1980s, extensive research has been carried out in the central part of the Olkiluoto
Island where ONKALO is currently located and the results have been used in the development of
site-scale models. The focus has then shifted since 2006 to the eastern part of the island which
was relatively poorly known whereas information was required for the potential enlargement of the
repository to the east. Consequently, additional drilling from the surface and surface-based
investigations were carried out in this part of the island, also driven by the data requirements for
future modelling studies and the design of ONKALO.
The monitoring programme includes rock mechanical, hydrogeological, hydrochemical and
biosphere monitoring. A forest monitoring system has notably been developed since 2003, which
includes microclimate monitoring.
A brief overview of the characterization activities performed over the period 2006-2008 at Olkiluoto,
which have contributed to the Hydrogeology Site Descriptive Modelling of 2009, is summarized in
Table 1-1.
All the scientific and technical information collected during the characterization activities was stored
in a knowledge management system (web-based system) composed of:
 The POTTI research data system which centralises the data from the site investigation
program and construction work;
 The VAHA requirement management system which documents the requirements for the final
disposal system; and
 The Kronodoc document management system which centralises all the written reports.

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Table 1-1 Summary of the main characterization activities performed over the period
2006-2008 at Olkiluoto, which have contributed to the Hydrogeology Site
Descriptive Modelling of 2009 (according to Posiva Oy, 2009).
Discipline Method Results
Investigation of outcrops and trenches Mapping of lithologies, ductile
deformation structures, fractures and
50 deep drillholes (which include one under the sea)
brittle deformation zones
Geology Geological mapping of ONKALO (lithology, fracturing,
Allows sampling and other detailed
foliation, alteration, Rock Quality Designation, joint
investigations in boreholes
aperture measurements, water leakages) and pilot hole
drilling
Standard geophysical logging methods (magnetic Study of rock alteration and deformation
susceptibility, resistivity, density, natural gamma structures (which includes the
radiation, full waveform sonic, calliper, fluid temperature identification of fractures),
and resistivity logging)
Monitoring of conductivity changes in the
Drillhole imaging tools (seismic imaging, magnetic bedrock indicating potential changes in
mapping, electromagnetic sounding and mise-à-la- the level of saline groundwater
masse surveys)
Characterization of Excavation Damaged
Geophysics Petrophysical sample measurements to support the Zones (EDZ) in ONKALO
interpretation of logging data

3D reflection seismic survey
Electromagnetic sounding in bore holes,
Crosshole tomographic test using radiowave imaging,
Seismic survey and mise-à-la-masse surveys in
ONKALO
Determination of surface runoff of the local catchment Data acquisition to support modelling and
areas with weirs and an automated measuring system assess future changes caused by the
construction of ONKALO
Long-term monitoring of the groundwater table and
measurement of hydraulic heads at depth with multi- Identification of hydraulically-conductive
packer systems fractures
Systematic measurement of hydraulic conductivity with Identification of hydraulic connections
Hydrology the DIFF (Difference Flow Meter) in all surface-based between boreholes
/Hydrogeology drillholes and the HTU (Hydraulic Testing Unit) in
Identification of borehole responses to
selected drillholes at repository depths
field activities
Electrical Conductivity logging, temperature logging,
measurement of the single point resistance of the
borehole wall
Systematic mapping of the inflow points into the
ONKALO tunnel
Sampling of deep and shallow ground waters with PAVE Identification of glacial inputs
(Pressurised Water Sampling Equipment)
Identification of changes caused by
Matrix pore water studies to get information about the ONKALO construction or long-term
groundwater quality in intact rock pumping
Hydro-
chemistry Identification of dissolve gases and
salinity distribution
Study of the potential variation of
groundwater composition over time

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1.3 Watershed Data Interpretation and Tools
1.3.1 Precipitation Data Interpretation Method and Tools
Precipitation data have been analysed by means of long-term statistical calculations and an extreme
value analysis (Haapanen, 2010) using MATLAB.
For modelling purposes, precipitation data (corrected for wind and evaporation losses) were
analysed together with potential evapotranspiration, interception and snow processes, in order to
delineate patches which formed homogenous units in terms of hydrological processes above the
soil over the Olkiluoto Island (Karnoven, 2008).
The difference between the amounts of precipitation between these areas was found to be most
likely related to topographic features (Karnoven, 2008). Moreover, a significant difference was
found between precipitation below forest canopy and over open areas (Haapanen 2007, 2010). The
amount of precipitation falling on the forest floor within the stands was strongly dependent on the
precipitation above the tree canopies. Although the canopy layer and forest structure had a major
effect on the amount of water in stand through fall, the precipitation in the open area was found to
be the most important factor regulating the amount of water passing to the forest floor in Finnish
conditions. The mean interceptions of precipitation by the tree crowns as percentage of the
precipitation in the open areas were 37, 28 and 29% in 2004, 2005 and 2006, respectively. The
difference between 2004 and 2005-2006 suggested that a higher proportion of total precipitation
occurred as snow during 2005-2006.
Snow accumulation and snow melt were found to be very well described by the degree-day method
originally developed by Vehviläinen (1992). This means that air temperature explained snow
processes well enough to be considered as the main input of the snow routine in surface modelling
(Karnoven, 2008).
1.3.2 Evapotranspiration Data Interpretation Method and Tools
Potential evapotranspiration was calculated using the Penman-Monteith equation (Karvonen and
Varis 1992). Actual evapotranspiration was deduced from surface hydrology modelling (Karnoven,
2008). A more sophisticated approach was developed in 2009 using a Soil-Vegetation-Atmosphere-
Transfer (SVAT) model (Karnoven, 2009) to analyse the different water and energy balance
components of the Forest Intensive monitoring plots (FIP) on Olkiluoto (cf. modelling section below).
1.3.3 Recharge Interpretation Method and Tools
Recharge computations were mainly carried out with the surface hydrology model (Karnoven,
2008).The interpretation of chemical and isotopic data also gave an insight into recharge processes
(Posiva Oy, 2009). Fresh HCO -type waters were found in shallow ground waters from overburden
3
and bedrock which signalled a recent terrestrial recharge during the last 0 – 2500 a. A mixing with
former ground waters (brackish HCO -type) was identified down to 100 – 150 m depth.
3
1.3.4 Groundwater Baseflow Interpretation Method and Tools
Discharge measurements were found to be the most important source of uncertainty in the water
balance computations in 2008 (Karnoven, 2008) for several reasons (leaking weirs, stream gages
on only 4 of the 15 watershed catchments, only one manual measurement once a week on each
weir). The groundwater base flow was explored through a surface modelling approach where less
weight was given to the discharge measurements during calibration of the soil parameters as
discharge values were uncertain.

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1.3.5 Groundwater Levels Interpretation Method and Tools
Heads have been measured on the Olkiluoto site since 1990. The measurements have included
monitoring of head in permanent piezometers, boreholes equipped with multi-packers and the
determination of heads in connection with flow logging (Ahokas 2008). Determination of the
hydraulic head of the packed-off intervals was conducted by measuring the water level in the hose,
which connects the monitoring interval to the ground surface. Two types of packer have been used
(inflatable rubber packers and fixed concrete packers). Water level in the hose is measured either
manually by a contact meter or by means of pressure transducers linked to an automatic data
acquisition system or data loggers. If the measurement hose is filled with fresh water, the measured
water level represents directly the fresh water head of the measurement section. In many cases the
water in the hose is mixed due to the intrusion of borehole water into the measuring hoses during
the installation (lowering) of the system. In that case, a density correction was applied as discussed
below.
The measured and calculated heads were converted into in situ fresh water heads, which
correspond to the water level (metres above sea level) in the hose that runs from the packed-off
section to the ground surface. This means that the determined head included the effects of
temperature and compressibility of water on the density of water.
These head corrections have thus consisted in:
 A density correction using density laboratory measurements corrected for temperature from
the depth of the test section. A similar correction was made in the conversion of measured
absolute pressures of flow logging into fresh water heads by calculating the compressibility
factor as a function of temperature (the effect of the water density on the compressibility
factor was neglected); and
 A normalization to represent the long-term mean of the chosen reference drill hole as the
period of observations may have coincided with a dry or wet period compared to the long-
term means. These periods were defined by comparing the average of the period in
question with the long-term means of some reference drill holes. The reference drill holes
were chosen as far away as possible from the central investigation area and were found not
to be sensitive to the disturbances caused by several kinds of field activities (pumping). The
seasonal correction factor was calculated by dividing the approximate means of the changes
in the reference wells by the corresponding changes in the different measuring levels. The
seasonal factor was found to decrease clearly with depth (Figure 1-2) which indicated that
bedrock heads were not dependent on fluctuations or seasonal variations of the groundwater
table below a certain depth (approx. -500 m).
The compilation of the equipotential lines of the mean groundwater table over the Olkiluoto Island
was carried out in 1993 (Ahokas and Herva 1993) and no significant changes have been found by
Vaittinen et al. (2009) although the observation network was much more comprehensive in 2009.
Corrected head deeper in the bedrock were compiled by Ahokas et al. (2008) to produce the so-
called baseline heads for different boreholes (Figure 1-3). The corrected hydraulic head data have
been analysed and compared to these baselines in order to:
 Identify hydraulic connections between drill holes;
 Determine the responses of drill hole packed-off sections to some field activities;

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 Compare the observed hydraulic connections with the previous hydrogeological model;
 All the measured head observations both in packed-off and in open drill holes were gathered
and a data processing code was developed to enable inquiries of head values for selected
field activities. The gathering of the data and the code improved interpretation and enabled
easy mutual comparison of head observations from several boreholes; and
 The results of this comparison analysis supported the concept of continuity of different main
sub-horizontal hydrogeological zones on the Olkiluoto Island (Vaittinen et al., 2009).

Figure 1-2 Changes in groundwater table levels and corresponding changes in measured
heads by depth in two drill holes (OL-KR12 and OL-KR29) in spring and
summer 2006. Factors represent the portion of magnitude of surface change
by depth (Ahokas et al., 2008).

1.3.6 Trend Analysis (Precipitation and Groundwater Levels) Interpretation Method and
Tools
As explained above, the groundwater heads have been corrected for seasonal variations (due to
wet or dry periods) on the basis of water level trend analyses on several reference boreholes which
were chosen to represent the most undisturbed conditions possible on the Olkiluoto Island. When
some difference was found between the observed head trend line and the long-term mean, the well
was excluded from the reference borehole group (cf. well PP9 in Figure 1-4). Several hypotheses
have been ventured to explain the recent increasing trend observed on PP9 for instance (effect of
infrastructures and building, change in hydraulic properties of some fractures around the well ) but

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