Artesian Aquifer South Coast of South Africa

An often quoted case study (Vogel, 1970) is that of an artesian aquifer in an area near the south coast of South Africa (Fig. 11.8). The decrease in 14C downslope from the aquifer has been taken by the researcher to indicate continuity. One can even calculate the velocity of groundwater flow in the aquifer by selecting two points on the lines of Fig. 11.8, for example, 2 km-4000 years and 18 km-28,000 years. The average flow velocity in the aquifer is

18-2

Fig. 11.8 14C ages (assuming initial concentration of 85pmc) of water samples from artesian wells near the south coast of South Africa as a function of the distance from the outcrop of water-bearing strata. (From Vogel, 1970.)

Table 11.6 Hydrological and Isotopic Data of Groundwaters in the Paris Basin z

Table 11.6 Hydrological and Isotopic Data of Groundwaters in the Paris Basin

Stratigraphic unit

hco3

Tritium

<513C

14C

No.

Region

Place

Aquifer

Source

tapped

Date

(meq/1)

(TU)

(%»)

(pmc)

1

Southeast

Parly-Chenons

Free

Well

Upp. Albian

10/66

0.3

77

94.7

2

Parly-Bernier

Free

Spring

Upp. Albian

10/66

3.1

27

86.7

3

Poilly

Free

Spring

Mid. Albian

10/66

5.1

9

91.7

4

Dracy

Confined

Drill

Upp. Albian

7/69

2.4

10

66.7

5

Chichery

Confined

Drill

Upp. & Mid.

7/69

2.4

l.d.*

-13.0

58.0

Chichery

Confined

Drill

Albian

4/66

l.d.

-17.7

53.2

6

Migennes

Confined

Drill

Upp. Albian

10/67

4.0

l.d

46.6

Migennes

Confined

Drill

Upp. Albian

7/69

3.8

21

67.3

7

Neuilly

Confined

Artesian

Upp. Albian

3/69

l.d.

- 15.0

15.9

8

Fleury

Confined

Artesian

Lower Albian

11/67

2.8

l.d

14.9

9

Champvallon

Confined

Artesian

Upp. Albian

3/69

l.d.

- 12.8

13.6

10

Grand-Chaumont

Free

Well

Cenomanian Chalk

7/69

4.7

95.6

11

Froville

Free

Well

Turonian

7/69

6

72.5

12

Appoigny

Confined

Artesian

Barremien

3/69

3.6

l.d.

- 18.3

0.6

Appoigny

Confined

Artesian

Barremien

10/67

l.d.

11.6

13

Grande Paroisse

Confined

Artesian

Albian

7/69

2.8

l.d.

3.2

14

Montbouy

Confined

Artesian

Upp. Albian

10/67

2.4

l.d.

28.9

15

East

Nuisement

Free

Drill

Albian

6/69

5.3

7

84.3

16

Humbecourt

Free

Drill

Albian & Aptian

6/69

4.48

208

76.9

17

Chaudefontaine

Confined

Drill

Albian & Aptian

6/69

6.8

10

74.8

18

Voillecomte

Free

Well

Albian & Aptian

6/69

2.2

l.d.

66.3

19

Montier-en-Der

Confined

Drill

Albian & Aptian

6/69

5.6

37

52.8

20

Dompremy

Confined

Artesian

Albian

6/69

5.2

l.d.

-9.0

17.9

21

Ste Ménéhoule

Confined

Artesian

Albian & Jurassic

6/69

l.d.

1.4

22

South

Barlieu

Confined

Drill

Albian & Cenomanien

10/67

4.7

l.d.

82.1

23

Biancafort

Confined

Drill

Albian &

10/67

3.9

l.d.

42.2

24

Chapelle Angilon

Confined

Drill

Cenomanien

11/67

4.1

l.d.

34.2

25

West

Bemecourt

Confined

Drill

Rauracian

5/69

2.8

- 13.2

75.5

26

Thiberville

Confined

Drill

Albian & Kimmeridgian

5/69

5.2

- 13.0

65.3

27

Brou

Confined

Drill

Albian

5/69

3.6

-9.0

Copyright © Marcel Dekker, Inc. All rights reserved.

28

Châteadun

Confined

29

Northwest

Gauciel

Confined

30

Marais-Verniet

Confined

31

Vernon

Confined

32

Les Logs

Confined

33

St. Pierre-en-Port

Confined

34

Le Trait

Confined

35

Mantes

Confined

36

Pont del'Arche

Confined

37

Hon fleur

Free

38

Incarville

Confined

39

Central

Epinay

Confined

40

Villeneuve

Confined

41

Achères

Confined

42

Ivry

Confined

43

Orsay

Confined

44

Le Pecq

Confined

Pantin

Confined

47

Issy

Confined

Noisy le Grand

Confined

48

Noisy le Grand

Confined

49

Paris ORTF

Confined

Aulnay sous Bois

Confined

Aulnay sous Bois

Confined

Aulnay sous Bois

Confined

50

ViryChatillion

Confined

Source: Extracted from Evin and Vuillaume (1970).

Artesian

Alhian

6/69

4.9

-5.7

40.9

Drill

Upp. Albian

7/68

4.1

-9.8

37.5

Well

Upp. Albian

7/68

4.4

l.d.

-14.2

36.9

Artesian

Albian

7/68

3.2

-8.2

21.7

Drill

Albian & Cenomanian

8/68

4.9

-9.6

15.9

Artesian

Upp. Albian

8/68

3.3

-11.4

16.0

Artesian

Upp. Albian

7/68

3.4

-10.9

12.4

Artesian

Upp. Albian

3/66

3.0

-10.9

12.4

Artesian

Up. Albian

11/67

4.1

l.d.

7.2

Spring

Cenomanian

7/68

5.8

12

-13.3

78.6

Artesian

Jurassic to Cenomanian

5/69

7.5

+ 2.9

1.4

Artesian

Albian

3/68

3.4

-13.2

9.7

Drill

Albian

6/67

2.7

l.d.

9.1

Drill

Albian

3/68

2.9

-16.3

8.9

Drill

Albian

1/68

3.2

8.5

-13.3

Drill

Albian

1/68

3.5

-10.6

7.8

Drill

Upp. Albian

3/68

2.6

-14.3

7.3

Drill

Albian & Barremian

12/66

2.6

-15.3

6.4

Drill

Albian

7/69

2.5

l.d.

-15.0

3.7

Artesian

Albian

3/68

3.1

-14.1

3.5

Artesian

Albian

8/69

3.1

3.7

Drill

Albian

2/67

2.6

-12.2

3.2

Drill

Albian

3/68

2.9

-16.4

2.7

Drill

Albian

3/68

2.9

l.d.

-95

1.0

Drill

Albian

10/69

2.9

2.6

Artesian

Albian

8/69

3.1

This case study is a good example for demonstrating the general idea of "expected" behavior and the application of 14C in aquifer studies. However, more data are needed in such cases:

• Points of sampling (in Fig. 11.8 a gap of 7 km exists between the central wells)

• Piezometric levels

• Temperatures

• Chemical compositions

• Isotopic compositions (e.g., dD, d18O, d13C, and tritium)

The continuity of the aquifer and active flow in it are independently checked by each of these parameters. This is essential because 14C may decrease with depth (and distance) also in cases of discontinuous flow. As a matter of fact, the obtained average flow velocity of 0.66m/year is extremely slow, and it might indicate lack of flow in parts of the system.

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