Permeabilities and Chemical Properties o
43
Aquatic Geochemistry 3: 43–60, 1997.
c 1997 Kluwer Academic Publishers. Printed in the Netherlands.
Permeabilities and Chemical Properties of Water in
Crystalline Rocks of the Black Forest, Germany
INGRID STOBER
Geologisches Landesamt Baden-W¨urttemberg, Albertstr. 5, D-79104 Freiburg i.Br., Germany
(Received: 12 October 1996; in final form: 18 March 1997)
Abstract. Investigations were carried out to determine the hydraulic and hydrochemical properties of
crystalline rocks in the Black Forest of Germany and neighbouring regions. Rock permeabilities ( )
were determined to a depth of 3500 m. These parameters range from = 3.5 10 10 m s 1 to =
8.7 10 5 m s 1 ; and can increase up to an order of magnitude which is typical for porous aquifers.
It is shown that on an average, granites are more pervious than gneisses and only the permeabilities
of gneisses decrease with depth.
The geochemistry of natural waters in crystalline rocks is not constant, but varies with depth and
location. The concentration increases with depth and the water-type changes from a Ca—Na—HCO3 type (or Na—Ca—HCO3 —) at shallow depths to a Na—Cl-type at greater depths. Thermal springs
are found only in granitic rocks with on average higher permeabilities than in gneisses. Thermal
waters are welling up in valleys at the bottom of steep mountains. The chemical composition of
thermal spring water is identical to that of water found at greater depths. Using geothermometers it
is found, that the depth of the deposits of thermal spring water in the crystalline basement rocks of
the Black Forest is some 1000 m below the surface. The topographic relief in the mountains induces
a deep circulation of infiltrating rain-water with an upwelling as thermal springs in the valleys.
K
K
K
Key words: crystalline rocks, hydraulic properties, hydrochemical properties, Black Forest.
1. Introduction
Super deep wells, such as the Kola well – situated in the former U.S.S.R – with
a depth of 12 500 m show, that there are open, waterfilled fissures in crystalline
rocks. The object of this investigation was to explore the rock permeabilities and
the chemical properties of water in the crystalline rocks of the Black Forest in
Germany and neighbouring regions (Figure 1).
The crystalline basement is being considered as a possible host rock for a
waste repository, because of its assumed low hydraulic conductivity. However,
hydrogeologic evidence shows, that there are several thermal and mineral water
springs in crystalline rocks, possibly contradicting assumptions of generalized
impermeable conditions.
The area of investigation (200 70 km) the crystalline basement of the Black
Forest was situated in Southwestern Germany. During the Variscan orogeny, the
crystalline basement underwent strong structural and metamorphic/hydrothermal
overprinting, accompanied by plutonic and volcanic activity. Since then, the lithology and structure of the basement have not changed significantly. During the
44
INGRID STOBER
Figure 1. Geological map of the Black Forest and neighbouring regions (South Western
Germany).
Tertiary period, following a period of relative tectonic inactivity that lasted about
200 million years, further changes occurred in the region, namely, the formation of
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
45
the Upper Rhine Graben, the updoming of the Black Forest and the formation of
the Folded Jura.
Results of rock conductivities and water chemistry in the study area are presented
below.
2. Hydraulic Methods
From pumping or injection tests, recharge tests, slug tests, water pressure tests,
tracer tests, fluid logging tests, earth tide methods among others it is possible to
determine in situ transmissivities and/or coefficients of permeability of rock strata.
Pumping or injection tests produce the best information about the aquifer, its
structure and properties (Figure 2a,b). Recharge and slug tests, only provide data on
the nearest domain around the well or borehole, but this part of the aquifer is very
often disarranged by drilling, well design, etc. To apply fluid-logging tests, much
additional information and measurement is necessary; additionally, the interpretation is based on restricted assumptions concerning the aquifer. Because earth-tide
forces are acting on extended areas of the whole earth, results from earth-tide methods are parameters integrated over very large areas and therefore difficult to interpret. Permeabilities from water-pressure tests are based on empirical assumptions,
and are not therefore considered in these investigations. Successful tracer-tests in
crystalline rocks are very difficult to conduct, because velocities are very small,
and flow-paths and flow-directions are mostly unknown (Stober, 1986; Reifenstahl
and Stober, 1990; Kruseman and de Ridder, 1991).
3. Hydraulic Data/Data Base
Mainly pumping tests exist. The oldest tests date from the 1950s, but are not a
quality criterion, because in former times people concentrated on getting steady
state (constant drawdown) during pumping-tests, and therefore these tests were
carried out very slowly and carefully.
Nevertheless the quality of the data, derived from the examined hydraulic tests,
differed greatly. It can be explained partly by the conception of that time. Frequently
a pumping test was only a trial, to see if water was present and test its quality.
Therefore several tests were carried out in a very short time, the withdrawal rate
oscillated very strongly or the registration of the data was scanty. Also, several tests
were carried out in thermal water, where special requirements to analyse a test are
necessary (Stober, 1986). In inclined wells measurements of the water level during
pumping tests had to be corrected.
About 400 hydraulic tests in crystalline rocks of the Black Forest and neighbouring regions were interpreted and permeabilities determined. Altogether there
are now permeabilities for 153 different localities in the crystalline rock under
consideration. In most instances the quality of the data permitted only the determi-
46
INGRID STOBER
Figure 2a. Typical drawdown – and recovery – curves during pumping tests in hard rock aquifers.
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
47
Figure 2b. Typical drawdown – and recovery – curves during pumping tests in hard rock aquifers.
48
INGRID STOBER
Figure 3. Distribution of the coefficient of permeability K in crystalline rocks.
Figure 4. Distribution of the coefficient of permeability K in granites and gneisses.
nation of transmissivities, rarely of storage coefficients and parameters describing
the geometry of fissures.
Because the length of the hydraulically tested rock mass differed from well
to well from a few meters up to several hundred meters, it was impossible to
compare transmissivities with one another. Therefore the transmissivities (T) were
standardized with the length of the hydraulically tested rock mass (H), K = T/H,
where K is the permeability.
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
49
4. Calculated Permeabilities (Transmissivities)
K
= 3.5
The permeabilities determined in gneiss and granite rocks vary from
10
1
5
1
10
= 8.7 10 m s , the accompanying transmissivities from
m s to
= 1.0 10 7 m2 /s to = 4.7 10 3 m2 /s. The range of both parameters is
wide. It is remarkable that the permeability – respectively the transmissivity – of
crystalline rocks can increase up to an order of magnitude, which is typical for
porous aquifers.
The permeabilities of the crystalline basement in the Black Forest are neither
lower nor higher than in other crystalline rocks (Table I).
The calculated permeabilities/transmissivities suggest a logarithmic normal distributed evenly (Figure 3), just as the permeabilities in pure granite and in pure
gneiss rocks (Figure 4). The analogous average values are:
K
T
T
Table I. Mean permeability in crystalline rocks of
the Black Forest
Rock
Mean permeability K (m/s)
Total crystalline
Granite
Gneiss
2.14 10
9.55 10
5.01 10
7
7
8
The averages are the arithmetic means of the logarithms of the individual values.
The highest values of the calculated permeabilities are found in boreholes in
granite rocks. Permeabilities in pure gneiss rocks turned out to be smaller. Of
course there is a smooth transition zone. Gneiss rocks with granitic intrusions take
an intermediate position.
The great difference between permeabilities in granite and gneiss rocks is not
confined to these rock types, there are also boreholes in granite rocks, which show
a very low permeability. The minerals in granites are very uniformly and randomly
distributed. If any tectonic stress is present, the behaviour of granite rocks is much
more rigid than that of gneisses. Gneisses are more elastic because of their texture,
which is characterized by mica plates in single layers. Therefore granites break
more easily than gneisses and are frequently more fractured and consequently they
are more permeable.
The permeability in granite rocks seems to be independent of depth, whereas in
gneiss rocks a distinct decrease of permeability with increasing depth exists (Figure
5).
Teollisuuden Voima Oy (1992) carried out detailed hydraulic investigations in
some wells of the Finnish bedrock. They discovered, that below a depth of 500–
600 m the permeabilities of the crystalline rocks decrease. The Nagra found similar
results in some deep wells in northern Switzerland (K¨upfer and Hufschmied, 1989).
50
INGRID STOBER
Figure 5. Coefficient of permeability K in dependence of depth.
Figure 6. Example for intensively fractured crystalline rock, acting like a homogeneous,
isotropic aquifer.
5. Flow Behaviour/Flow Path
By analysing pumping test data it was possible, to get some idea of the flow
behaviour in crystalline rocks:
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
51
Figure 7. Example for the influence of a fault-line, simulating hydraulic boundaries.
In intensively fractured crystalline rocks the hydraulic reaction is the same as
in a homogeneous, isotropic aquifer (Figure 6). This flow behaviour is typical
for granite rocks (cap. 4).
Near faults/fault-lines, dykes or mineral veins the pumping test data revealed
the influence of hydraulic boundaries (Figure 7).
The hydraulic behaviour in wells, getting water from only a few fractures,
corresponds to the theoretical model of single vertical, horizontal or inclined
fractures in homogeneous, isotropic aquifers (Figure 8).
Descriptions of drilling foremen and geophysical logs in boreholes together with
geological profiles show, that water-bearing complexes are attached to
Faults/fault-lines, rock masses extremely strained by tectonic forces and cracked,
sheared rocks (breccia).
52
INGRID STOBER
Figure 8. Example for the model of a horizontal fracture in a homogeneous isotropic aquifer.
Contact areas between granites, granite dykes and granite porphyries on the
one hand and gneisses on the other; intensively fissured granite dykes within
paragneisses.
Old circulation-paths, like: hydrothermal altered or strained areas, mineral
veins, or open fractures filled with minerals.
The magnitude of the permeability in crystalline rocks is supposed to depend on
those characteristics. Biotit-rich gneisses on the other hand have extremely low
permeability (cap. 4).
6. Geochemistry of Natural Waters in Crystalline Rocks
About 200 checked chemical analyses of water within crystalline rocks of the
Black Forest were briefly interpreted by Stober (1993). The complete analyses
are published in Stober (1993). The groundwater composition is used to trace the
origin of thermal springs in the Black Forest. The geochemistry of groundwater in
crystalline rocks is not uniform but broadly variable as shown on Figure 9a. Some
examples for groundwater analyses are given in Table III.
It turned out, that groundwater-quality is changing with depth:
The total concentration of the dissolved substances in water is increasing
with depth as is shown on Figure 9b. At a depth of more than 2000–3000 m
below surface the total concentration of dissolved substances will be more
than 5000 mg/kg.
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
Figure 9a. Data of chemical analyses in crystalline basement rocks.
Figure 9b. Total concentration of water in crystalline basement depend on depth.
53
54
Table II. Selected chemical analyses of characteristic waters in crystalline basement rocks
Name/location
pH
H2 SiO3
(mg/kg)
Na
(meq/kg)
K
(meq/kg)
Ca
(meq/kg)
Mg
(meq/kg)
Cl
(meq/kg)
HCO3
(meq/kg)
SO4
(meq/kg)
Bad.-Bad.
Freyersbach
Herrenalb
Liebenzell B11
Liebenzell Hel.
Peterstal Q.6
Rippoldsau
S¨ackingen Frid.
Wildbad B.III
Wildbad B.IV
7.06
6.24
7.25
7.15
6.90
6.12
5.90
6.60
6.94
7.07
137.03
106.70
19.00
38.00
24.10
17.60
58.10
22.00
59.00
73.32
32.98
12.22
27.85
14.50
13.00
16.61
16.78
96.57
6.15
6.01
1.33
0.49
0.34
0.56
0.42
0.56
0.61
3.67
0.21
0.22
5.49
16.39
9.25
2.21
2.40
20.83
21.71
13.36
1.80
1.70
0.30
5.40
1.34
0.65
0.90
5.07
5.97
1.72
0.25
0.25
35.93
0.78
24.56
11.61
9.70
1.00
1.35
99.85
4.00
3.83
2.61
25.80
2.20
5.35
5.70
31.72
27.38
8.41
3.65
3.80
3.11
8.05
12.69
1.16
1.44
10.69
16.04
7.31
0.79
0.65
INGRID STOBER
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
55
Figure 10a. Na-portion in waters of crystalline rocks depend on depth.
Figure 10b. Cl-portion in waters of crystalline rocks dependent on depth.
The character of groundwater quality changes from a Ca—Na—HCO 3 -type
(or Na—Ca—HCO3—) near surface over a Na—Ca—SO4 —HCO3 -type at
medium depth to a Na—Cl-type at great depth (Figure 10a,b). Figure 10a
illustrates for example that at depths greater then 300 m the concentration of
the Na-ions will be more than 45 equ.%. Table IV shows the main contents of
deep crystalline groundwaters in the Black Forest.
High CO2 gas contents in the crystalline waters of the Black Forest accelerate the
water-rock interaction, dissolution and weathering. Table IV shows the approximate
composition of groundwater with high CO2 -concentrations (>3000–4000 mg/kg).
56
INGRID STOBER
Table III. Main contents of deep crystalline groundwaters
Cations (equ.%)
Na+
Ca2+
Mg2+
Anions (equ.%)
90
Aquatic Geochemistry 3: 43–60, 1997.
c 1997 Kluwer Academic Publishers. Printed in the Netherlands.
Permeabilities and Chemical Properties of Water in
Crystalline Rocks of the Black Forest, Germany
INGRID STOBER
Geologisches Landesamt Baden-W¨urttemberg, Albertstr. 5, D-79104 Freiburg i.Br., Germany
(Received: 12 October 1996; in final form: 18 March 1997)
Abstract. Investigations were carried out to determine the hydraulic and hydrochemical properties of
crystalline rocks in the Black Forest of Germany and neighbouring regions. Rock permeabilities ( )
were determined to a depth of 3500 m. These parameters range from = 3.5 10 10 m s 1 to =
8.7 10 5 m s 1 ; and can increase up to an order of magnitude which is typical for porous aquifers.
It is shown that on an average, granites are more pervious than gneisses and only the permeabilities
of gneisses decrease with depth.
The geochemistry of natural waters in crystalline rocks is not constant, but varies with depth and
location. The concentration increases with depth and the water-type changes from a Ca—Na—HCO3 type (or Na—Ca—HCO3 —) at shallow depths to a Na—Cl-type at greater depths. Thermal springs
are found only in granitic rocks with on average higher permeabilities than in gneisses. Thermal
waters are welling up in valleys at the bottom of steep mountains. The chemical composition of
thermal spring water is identical to that of water found at greater depths. Using geothermometers it
is found, that the depth of the deposits of thermal spring water in the crystalline basement rocks of
the Black Forest is some 1000 m below the surface. The topographic relief in the mountains induces
a deep circulation of infiltrating rain-water with an upwelling as thermal springs in the valleys.
K
K
K
Key words: crystalline rocks, hydraulic properties, hydrochemical properties, Black Forest.
1. Introduction
Super deep wells, such as the Kola well – situated in the former U.S.S.R – with
a depth of 12 500 m show, that there are open, waterfilled fissures in crystalline
rocks. The object of this investigation was to explore the rock permeabilities and
the chemical properties of water in the crystalline rocks of the Black Forest in
Germany and neighbouring regions (Figure 1).
The crystalline basement is being considered as a possible host rock for a
waste repository, because of its assumed low hydraulic conductivity. However,
hydrogeologic evidence shows, that there are several thermal and mineral water
springs in crystalline rocks, possibly contradicting assumptions of generalized
impermeable conditions.
The area of investigation (200 70 km) the crystalline basement of the Black
Forest was situated in Southwestern Germany. During the Variscan orogeny, the
crystalline basement underwent strong structural and metamorphic/hydrothermal
overprinting, accompanied by plutonic and volcanic activity. Since then, the lithology and structure of the basement have not changed significantly. During the
44
INGRID STOBER
Figure 1. Geological map of the Black Forest and neighbouring regions (South Western
Germany).
Tertiary period, following a period of relative tectonic inactivity that lasted about
200 million years, further changes occurred in the region, namely, the formation of
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
45
the Upper Rhine Graben, the updoming of the Black Forest and the formation of
the Folded Jura.
Results of rock conductivities and water chemistry in the study area are presented
below.
2. Hydraulic Methods
From pumping or injection tests, recharge tests, slug tests, water pressure tests,
tracer tests, fluid logging tests, earth tide methods among others it is possible to
determine in situ transmissivities and/or coefficients of permeability of rock strata.
Pumping or injection tests produce the best information about the aquifer, its
structure and properties (Figure 2a,b). Recharge and slug tests, only provide data on
the nearest domain around the well or borehole, but this part of the aquifer is very
often disarranged by drilling, well design, etc. To apply fluid-logging tests, much
additional information and measurement is necessary; additionally, the interpretation is based on restricted assumptions concerning the aquifer. Because earth-tide
forces are acting on extended areas of the whole earth, results from earth-tide methods are parameters integrated over very large areas and therefore difficult to interpret. Permeabilities from water-pressure tests are based on empirical assumptions,
and are not therefore considered in these investigations. Successful tracer-tests in
crystalline rocks are very difficult to conduct, because velocities are very small,
and flow-paths and flow-directions are mostly unknown (Stober, 1986; Reifenstahl
and Stober, 1990; Kruseman and de Ridder, 1991).
3. Hydraulic Data/Data Base
Mainly pumping tests exist. The oldest tests date from the 1950s, but are not a
quality criterion, because in former times people concentrated on getting steady
state (constant drawdown) during pumping-tests, and therefore these tests were
carried out very slowly and carefully.
Nevertheless the quality of the data, derived from the examined hydraulic tests,
differed greatly. It can be explained partly by the conception of that time. Frequently
a pumping test was only a trial, to see if water was present and test its quality.
Therefore several tests were carried out in a very short time, the withdrawal rate
oscillated very strongly or the registration of the data was scanty. Also, several tests
were carried out in thermal water, where special requirements to analyse a test are
necessary (Stober, 1986). In inclined wells measurements of the water level during
pumping tests had to be corrected.
About 400 hydraulic tests in crystalline rocks of the Black Forest and neighbouring regions were interpreted and permeabilities determined. Altogether there
are now permeabilities for 153 different localities in the crystalline rock under
consideration. In most instances the quality of the data permitted only the determi-
46
INGRID STOBER
Figure 2a. Typical drawdown – and recovery – curves during pumping tests in hard rock aquifers.
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
47
Figure 2b. Typical drawdown – and recovery – curves during pumping tests in hard rock aquifers.
48
INGRID STOBER
Figure 3. Distribution of the coefficient of permeability K in crystalline rocks.
Figure 4. Distribution of the coefficient of permeability K in granites and gneisses.
nation of transmissivities, rarely of storage coefficients and parameters describing
the geometry of fissures.
Because the length of the hydraulically tested rock mass differed from well
to well from a few meters up to several hundred meters, it was impossible to
compare transmissivities with one another. Therefore the transmissivities (T) were
standardized with the length of the hydraulically tested rock mass (H), K = T/H,
where K is the permeability.
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
49
4. Calculated Permeabilities (Transmissivities)
K
= 3.5
The permeabilities determined in gneiss and granite rocks vary from
10
1
5
1
10
= 8.7 10 m s , the accompanying transmissivities from
m s to
= 1.0 10 7 m2 /s to = 4.7 10 3 m2 /s. The range of both parameters is
wide. It is remarkable that the permeability – respectively the transmissivity – of
crystalline rocks can increase up to an order of magnitude, which is typical for
porous aquifers.
The permeabilities of the crystalline basement in the Black Forest are neither
lower nor higher than in other crystalline rocks (Table I).
The calculated permeabilities/transmissivities suggest a logarithmic normal distributed evenly (Figure 3), just as the permeabilities in pure granite and in pure
gneiss rocks (Figure 4). The analogous average values are:
K
T
T
Table I. Mean permeability in crystalline rocks of
the Black Forest
Rock
Mean permeability K (m/s)
Total crystalline
Granite
Gneiss
2.14 10
9.55 10
5.01 10
7
7
8
The averages are the arithmetic means of the logarithms of the individual values.
The highest values of the calculated permeabilities are found in boreholes in
granite rocks. Permeabilities in pure gneiss rocks turned out to be smaller. Of
course there is a smooth transition zone. Gneiss rocks with granitic intrusions take
an intermediate position.
The great difference between permeabilities in granite and gneiss rocks is not
confined to these rock types, there are also boreholes in granite rocks, which show
a very low permeability. The minerals in granites are very uniformly and randomly
distributed. If any tectonic stress is present, the behaviour of granite rocks is much
more rigid than that of gneisses. Gneisses are more elastic because of their texture,
which is characterized by mica plates in single layers. Therefore granites break
more easily than gneisses and are frequently more fractured and consequently they
are more permeable.
The permeability in granite rocks seems to be independent of depth, whereas in
gneiss rocks a distinct decrease of permeability with increasing depth exists (Figure
5).
Teollisuuden Voima Oy (1992) carried out detailed hydraulic investigations in
some wells of the Finnish bedrock. They discovered, that below a depth of 500–
600 m the permeabilities of the crystalline rocks decrease. The Nagra found similar
results in some deep wells in northern Switzerland (K¨upfer and Hufschmied, 1989).
50
INGRID STOBER
Figure 5. Coefficient of permeability K in dependence of depth.
Figure 6. Example for intensively fractured crystalline rock, acting like a homogeneous,
isotropic aquifer.
5. Flow Behaviour/Flow Path
By analysing pumping test data it was possible, to get some idea of the flow
behaviour in crystalline rocks:
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
51
Figure 7. Example for the influence of a fault-line, simulating hydraulic boundaries.
In intensively fractured crystalline rocks the hydraulic reaction is the same as
in a homogeneous, isotropic aquifer (Figure 6). This flow behaviour is typical
for granite rocks (cap. 4).
Near faults/fault-lines, dykes or mineral veins the pumping test data revealed
the influence of hydraulic boundaries (Figure 7).
The hydraulic behaviour in wells, getting water from only a few fractures,
corresponds to the theoretical model of single vertical, horizontal or inclined
fractures in homogeneous, isotropic aquifers (Figure 8).
Descriptions of drilling foremen and geophysical logs in boreholes together with
geological profiles show, that water-bearing complexes are attached to
Faults/fault-lines, rock masses extremely strained by tectonic forces and cracked,
sheared rocks (breccia).
52
INGRID STOBER
Figure 8. Example for the model of a horizontal fracture in a homogeneous isotropic aquifer.
Contact areas between granites, granite dykes and granite porphyries on the
one hand and gneisses on the other; intensively fissured granite dykes within
paragneisses.
Old circulation-paths, like: hydrothermal altered or strained areas, mineral
veins, or open fractures filled with minerals.
The magnitude of the permeability in crystalline rocks is supposed to depend on
those characteristics. Biotit-rich gneisses on the other hand have extremely low
permeability (cap. 4).
6. Geochemistry of Natural Waters in Crystalline Rocks
About 200 checked chemical analyses of water within crystalline rocks of the
Black Forest were briefly interpreted by Stober (1993). The complete analyses
are published in Stober (1993). The groundwater composition is used to trace the
origin of thermal springs in the Black Forest. The geochemistry of groundwater in
crystalline rocks is not uniform but broadly variable as shown on Figure 9a. Some
examples for groundwater analyses are given in Table III.
It turned out, that groundwater-quality is changing with depth:
The total concentration of the dissolved substances in water is increasing
with depth as is shown on Figure 9b. At a depth of more than 2000–3000 m
below surface the total concentration of dissolved substances will be more
than 5000 mg/kg.
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
Figure 9a. Data of chemical analyses in crystalline basement rocks.
Figure 9b. Total concentration of water in crystalline basement depend on depth.
53
54
Table II. Selected chemical analyses of characteristic waters in crystalline basement rocks
Name/location
pH
H2 SiO3
(mg/kg)
Na
(meq/kg)
K
(meq/kg)
Ca
(meq/kg)
Mg
(meq/kg)
Cl
(meq/kg)
HCO3
(meq/kg)
SO4
(meq/kg)
Bad.-Bad.
Freyersbach
Herrenalb
Liebenzell B11
Liebenzell Hel.
Peterstal Q.6
Rippoldsau
S¨ackingen Frid.
Wildbad B.III
Wildbad B.IV
7.06
6.24
7.25
7.15
6.90
6.12
5.90
6.60
6.94
7.07
137.03
106.70
19.00
38.00
24.10
17.60
58.10
22.00
59.00
73.32
32.98
12.22
27.85
14.50
13.00
16.61
16.78
96.57
6.15
6.01
1.33
0.49
0.34
0.56
0.42
0.56
0.61
3.67
0.21
0.22
5.49
16.39
9.25
2.21
2.40
20.83
21.71
13.36
1.80
1.70
0.30
5.40
1.34
0.65
0.90
5.07
5.97
1.72
0.25
0.25
35.93
0.78
24.56
11.61
9.70
1.00
1.35
99.85
4.00
3.83
2.61
25.80
2.20
5.35
5.70
31.72
27.38
8.41
3.65
3.80
3.11
8.05
12.69
1.16
1.44
10.69
16.04
7.31
0.79
0.65
INGRID STOBER
PERMEABILITIES AND CHEMICAL PROPERTIES OF WATER IN CRYSTALLINE ROCKS
55
Figure 10a. Na-portion in waters of crystalline rocks depend on depth.
Figure 10b. Cl-portion in waters of crystalline rocks dependent on depth.
The character of groundwater quality changes from a Ca—Na—HCO 3 -type
(or Na—Ca—HCO3—) near surface over a Na—Ca—SO4 —HCO3 -type at
medium depth to a Na—Cl-type at great depth (Figure 10a,b). Figure 10a
illustrates for example that at depths greater then 300 m the concentration of
the Na-ions will be more than 45 equ.%. Table IV shows the main contents of
deep crystalline groundwaters in the Black Forest.
High CO2 gas contents in the crystalline waters of the Black Forest accelerate the
water-rock interaction, dissolution and weathering. Table IV shows the approximate
composition of groundwater with high CO2 -concentrations (>3000–4000 mg/kg).
56
INGRID STOBER
Table III. Main contents of deep crystalline groundwaters
Cations (equ.%)
Na+
Ca2+
Mg2+
Anions (equ.%)
90