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The spatial distribution of polluted groundwater from rural centres in a recharge area in the Netherlands — The Veluwe
The Science of the Total Environment, 21 (1981) 105--112 Elsevier Scientific Publishing C o m p a n y , A m s t e r d a m -- Printed in The Netherlands
105
THE SPATIAL DISTRIBUTION OF POLLUTED GROUNDWATER FROM RURAL CENTRES IN A RECHARGE AREA IN THE NETHERLANDS - THE VELUWE L. VASAK, G.J.W. KRAJENBRINK and C.A.J. APPELO Instituut
voor Aardwetenschappen, V r i j e U n i v e r s i t e i t
Amsterdam
ABSTRACT A t o p o g r a p h i c a l l y e l e v a t e d area of ice-pushed r i d g e s was s e l e c t e d f o r a study on groundwater chemical composition in r e l a t i o n
to the p o t e n t i a l
pollution
sources.
A groundwater sampling technique using small ceramic cups was adapted f o r t h i s study. This technique a l l o w s d e t a i l e d sampling in depth f o r each b o r e h o l e , even in areas w i t h deep groundwater l e v e l s . Results of the chemical analyses show g r e a t v a r i a t i o n s
in v e r t i c a l
of the i o n - c o n c e n t r a t i o n s in groundwater. These v a r i a t i o n s r e f l e c t
distribution
the d i f f e r e n c e s
in land use and are also shown to be a f u n c t i o n of the groundwater f l o w p a t t e r n s .
INTRODUCTION In May 1979 a hydrochemical study was s t a r t e d in the NW p a r t of the Veluwe in the province of G e l d e r l a n d . The purpose of t h i s study was to e v a l u a t e the q u a l i t y of groundwater as a f f e c t e d by f a c t o r s such as p r e c i p i t a t i o n t y p e , land use and in p a r t i c u l a r
composition, soil
the disposal of manure and use o f f e r t i l i s e r s ,
The N~J p a r t of the Veluwe is a r e g i o n where i n t e n s i v e c a t t l e - f a r m i n g
has been
p r a c t i s e d during the past 20 y e a r s . An ever i n c r e a s i n g p r o d u c t i o n of manure on the one hand and a lack o f space on the o t h e r have r e s u l t e d in the d i s p o s a l of excessive a m o u ~ s o f manure on small areas. Under c e r t a i n h y d r o g e o l o g i c a l and biochemical c o n d i t i o n s , some manure and fertiliser
compounds may reach the s a t u r a t e d zone and hence p o l l u t e the ground-
w a t e r . Good q u a l i t y o f groundwater is e s s e n t i a l in the Veluwe, since i t
is an
i m p o r t a n t recharge area f o r d r i n k i n g water s u p p l i e s . STUDY AREA The Veluwe is a t o p o g r a p h i c a l l y e l e v a t e d area of ice-pushed r i d g e s bordered in the west and east by two v a l l e y s , p e c t i v e l y (see f i g .
the Gelderse V a l l e y and the IJssel V a l l e y res-
I).
0 0 4 8 - 9 6 9 7 / 8 1 / 0 0 0 0 - - 3 0 0 0 / $ 0 2 . 7 5 © 1981 Elsevier Scientific Publishing C o m p a n y
106
t
Drn i
(after
Fig~ 1o
N e l n a r d l f l 974
~¢
0
5I
110 km
Location of the study area~
Geological structure of the Veluwe is rather complex. The subsurface preglacial Pleistocene sediments consist of marine and f l u v i a l sands and clays° During the Saalian (= Riss-lce Age), the older Pleistocene sediments were pushed and new, g l a c i a l (boulder clay) and g l a c i o f l u v i a l (sand, gravel and clay) sediments were l a i d down° Aeolian sands formed during the l a s t Ice Age in Weichselian times (= WUrm) cover these ice-pushed ridges. Two main soil types can be distinguished in the Veluwe : podzolic and noncalcareous sand-soilso In the areas surrounding old rural centres mineral rich s o i l s were developed as a r e s u l t of human a c t i v i t i e s (long term manuring). The Veluwe is a recharge area with a mean annual p r e c i p i t a t i o n of 840 mm and an estimated evapotranspiration of 470 mm ( r e f . i ) . The i n f i l t r a t i n g
precipitation
excess is d i s t r i b u t e d by groundwater flow to the lower ly in g areas surrounding the Veluwe ( r e f . 2). The most important aquifer consists of Pleistocene sands and gravels with varying k-values (mean value + 60 m/day), l a i d down before and during the R i s s - g l a c i a t i o n . This a q u i fe r is up to 200 m thick and i t s base is formed by impervious Early Pleistocene marine clays° At locations where f l u v i a l and g l a c i o f l u v i a l clays occur, two or more aquifers can be distinguished. In the higher parts of the Veluwe, depths to groundwater exceed 25 m. Groundwater levels can be l o c a l l y effected by pumping stations~ A large part of the Veluwe region is covered by f o r e s t and heath which are source
areas of good q u a l i t y groundwater. The remaining c u l t i v a t e d areas consist
mainly of grassland and arable land with corn, beet and potato f i e l d s . The p o l l u t i o n sources in these areas may cause contamination of deep groundwater, due to the high permeability of the sediments, the aerobic conditions, and absence of organic matter w i t h i n the aquifer°
107 METHODS AND MATERIALS P r e l i m i n a r y e v a l u a t i o n of the h y d r o g e o l o g i c a l and chemical data obtained from e x i s t i n g w e l l s in the NW Veluwe led to the s e l e c t i o n of two small areas f o r more d e t a i l e d study, The l o c a t i o n s of these areas are shown in ~ig. 2. I
Fig. 2.
Sampling s i t e s and groundwater f l o w in the Koudhoorn and Garderen areas.
Both areas can be c h a r a c t e r i z e d as r u r a l centres w i t h i n t e n s i v e c a t t l e
farming
A b r i e f d e s c r i p t i o n of the two areas is given in t a b l e I . TABLE i C h a r a c t e r i s t i c s o f the s t u d i e d areas Location Garderen Koudhoorn
Elevation (m+m.s.l.)
Mean depth to g,w.(m)
Farm land area (ha)
35 - 45 20 - 30
20 11
380 100
Grass/arable land r a t i o 4 : I 9 : i
Manure prod. (ton N / y r . ) 83.23 17.23
Ene groundwater f l o w p a t t e r n in both areas is complex due to non-honlogeneity of the a q u i f e r . To the west (downstream) of Koudhoorn the f l o w is also a f f e c t e d by a pumping s t a t i o n (see f i g .
2).
In these two areas 11 borings were c a r r i e d out to depth which v a r i e d from 13 to 75 m, Locations o f the seven b o r i n g s i t e s discussed in t h i s paper are shown in f i g .
2. One b o r i n g is s i t u a t e d in the f o r e s t and the remainder are located in •
/
or immediately a d j a c e n t to farm land. Porous ceramic cups, commonly used in s o i l m o i s t u r e studies ( r e f .
3 ) , were
adapted f o r the groundwater sampling programme. This technique allows d e t a i l e d sampling in depth f o r each borehole even in a s i t u a t i o n w i t h deep groundwater l e v e l s ( , 8 m). C o n s t r u c t i o n d e t a i l s of the ceramic cup device are schematized in f i g .
3.
The groundwater samples were analyzed a t the I n s t i t u t e
of Earth Sciences
l a b o r a t o r y in Amsterdam. Nitrogen compound c o n c e n t r a t i o n s (NO3, NO2 and NH~) were determined on a Technicon A u t o a n a l y z e r , HCO and Cl
c o n c e n t r a t i o n s were
108 log
G2
o~ 5~
Lithology ~fine
r~
..... ~coarse
~o~ 15q
sand
!!ii
0
sand
~grevel Ioern
[]~]
g i?
20q
-I-ground
water
level
25q
30-I
'::i
354 ~ ceramic
'~:
pVC pipe ( ¢ 16 mill) (reservoir)
cups
see detail ~
404
45-4
~
5O J
Fig° 3.
screen
(~ 2 8 m m )
Construction details of the ceramic cup device for sampling uf deep groundwater° obtained by t i t r a t i o n ,
I~8~
~H4
~27
~L
,
. . . . . .
~.
c~
•
<
. . . .
,~
cL . o 3
turbidiometrical
~o4 No3
.
,
.
SO
by a
procedure, and
PO~- ions were determined c o l o r i -
,
,.o
metrically. A flame spectrometer
3~7~ r,
was used for the K+ analyses. All other cations were determined by ICP-emission spectrometry. Re-
,6
sults of the analyses are stored on magnetic tape for further processing ( r e f . 4)°
/
?
Cumulative diagrams are used here ?
for presentation of the analyses reL?
sults. In these diagrams, the con-
~ : ' ,'3
centrations of major ions (in meq/l) 3~
3S
are added and plotted against depth of sample (see f i g . 4).
3" 38
r
J
5~
41
4t
Fig° 4
Cumulative diagram showing ion-concentration variations with depth.
109
i¸
%,-
, •
i.
S I
:
I1:
| | I I I I I l I II I II ~ I I I
'~'"f7
--~
I I I II]]
lillillill
[i
3
] | l l l l l l , . , , , , , l l l , . , , ,
N K ..............................................................................
F
i~
. :~i~
"
0 0 ~q
.
0
p
;5
| O
/
4~
lllllllllllllllllllllli,,~lllllll
IIIIIIIIIliillltl,,,,,ll
~4~
¸
£
....
:
.
i ¸ 4~
i
i i i ~,iiii
i i
rc~
O
(D
O
t)
| - -
....
A
~,,,[~tttttlllllllllllll
,a I t i l l l l l l l l l l l l l l l l l l l t ~ i l l ~ t
G" O ~D
~
,zl
:'k -, •
~-~ ~!~.
, Lx~
cJ-
-
Ii0 RESULTS AND DISCUSSION Meinardi ( r e f . I) found that chemical composition of reference (unpolluted) groundwater from the Veluwe region is s i m i l a r to that f o r rain water, m u l t i p l i e d by an evapotranspiration f a c t o r . This evapotranspiration f a c t o r , which depends on the vegetation cover, was estimated to be 2.2 and i t s use results in estimated concentrations in the annual p r e c i p i t a t i o n excess given below :
CI-
SO#[ HC03 NO3
9
I0
6
1
Na+
Mg2+
Ca2+
NHZ
7
2.5
3.5
1
(mg/l)
*may have changed in recent years Similar concentrations, with the exception of Ca2+ and HC03 ions, are commonly found in the deep groundwater beneath the whole Veluwe region ( r e f . i ) and in upper parts of the a q u i f e r in the heath and f o r e s t areas ( r e f . 5). The concentrations of Ca2+ and HC03 ions are greater (up to 50 and 150 mg/l respectively) due to s o l u t i o n of CaCO3 from the aquifer sediments. Concentrations of the other ions are more or less uniform over the whole Veluwe, since the aquifer consists princ i p a l l y of sands containing up to 98 % unreactive quartz. Due this unique s i t u a t i o n a p o l l u t i o n index of groundwater is r e a d i l y defined : any substantial increase of the above ion concentrations can be considered as pollution. Variations in ion concentrations with depth at the seven sampling sites are shown in f i g s . 4 and 5o The water q u a l i t y which is s i m i l a r to that f or the reference water is indicated by arrows. I t can be seen that this reference water q u a l i t y is e i t h e r absent or is present in only a minor part of the studied p r o f i l e . A l l chemical p r o f i l e s show great v a r i a t i o n s of TDS concentrations with depth and the concentrations of i n d i v i d u a l ions can increase or decrease r a p i d l y (within I m). Table 2 shows the minimum and maximum concentrations of major ions (in mg/l) at the seven sampling sites in Koudhoorn and Garderen. TABLE 2 Minimum and maximum concentrations (mg/l) of major ions at the sampling sites in Koudhoorn (K) and Garderen (G) Sample Site
~Jmho 's/cm EC min.
mg/l M g ++
Ca ~ ~
max.
min.
max.
550
l.l
15.7
c~-
Na+
K+
~o~
.c%
mil~. max.
min.
max.
min.
max.
min.
max.
min
17.9
40.1
0.6
16.3
6.2
I,I.6
19.4
,I,I.6
17.6
83.1
2
32
i,I
63
8.5
15
10
0.5
[
248
8
47
26.2
1
183
11
58
16.1
I
188
160
9
69
1.1
i
2,17
K2
155
K3
210
725
3.9
17.4
11.0
86.6
3.9
33.0
6.1
25.3
12,8
37.9
20.0
K4
160
48O
i.I
7,7
17.6
57.7
O,S
6,5
4.7
21.2
9.7
36.1
16,8
K6
280
1050
3.2
12.4
40.5
156
6.8
9.9
8.2
39.2
26.6
55.7
38.,1
GI
520
850
3.8
11.4
71.7
i18
I.I
2.7
11,7
32.,I
G2
32O
870
3.8
II.0
41.3
131
1.2
8.7
11.4
28.7
20,0
65.2
G3
195
820
i,i
13.1
2,1.9
105
0,6
6.1
7.1
18.4
13..I
34. 1
106 ,
166 82.2
max.
~o~
max.
min.
min
f
1.0
max 163
156 57. 248
111
The concentrations of K+, Na+, Mg2+, C l - , SO~~ and NO~ can be many times g r e a t e r than those c a l c u l a t e d f o r the reference water. The maximum NO3 c o n c e n t r a t i o n exceeds 50 mg/l at a l l sampling s i t e s ,
t h i s value being the upper l i m i t
recommended
f o r d r i n k i n g water purposes. The peak c o n c e n t r a t i o n of 248 mg/l was found at sampling s i t e K6, immediately below the groundwater t a b l e . However, n i t r a t e concentrations of more than 100 mg/l have also been recorded at depths which are considerably below the groundwater t a b l e . For example : s i t e K3 : 143 mg/l at 34 m below groundwater t a b l e (43 m below the surface) K6 : 104 mg/l "
17 m
.
.
.
.
.
.
(30 m
. . . . . .
)
G2 : 125 mg/l "
14 m
.
.
.
.
.
.
(38 m
. . . . . .
)
There are three p o t e n t i a l p o l l u t i o n - s o u r c e s in the studied areas : - manure production from the i n t e n s i v e c a t t l e farming - use of f e r t i l i s e r s -
domestic sewage ( i n c l u d i n g the camping grounds). Data on the use of f e r t i l i s e r s
have not y e t been obtained° The two other sources
can be q u a n t i f i e d approximately on the basis of i n h a b i t a n t e q u i v a l e n t numbers ( i . e ~ ) : manure production : domestic sewage
:
Koudhoorn
Garderen
7°858
51~143
952
2~350
These f i g u r e s i n d i c a t e t h a t manure production can be considered as the main source of p o l l u t i o n in Koudhoorn and Garderen when compared with the output of domestic sewage~ The composition of i n f i l t r a t i n g
water in the manured farming areas is determined
by the manure type (from cows, calves, pigs and p o u l t r y ) , the q u a n t i t y of manure transported to the land, the period of manuring and by the crop cover and s o i l type. The t r a n s p o r t of p o l l u t e d water in the saturated zone depends on hydrogeological c h a r a c t e r i s t i c s of the studied area~ Despite the f a c t t h a t the hydrogeological s i t u a t i o n is in a general sense known, the l o c a l f l o w patterns are poorly defined~ Consequently, the d e t a i l e d r e l a t i o n s h i p s between the h o r i z o n t a l v a r i a t i o n s in land use and the v e r t i c a l
v a r i a t i o n s in the composition of groundwater have not y e t been
determined in the present study phase° The complex s i t u a t i o n may be b r i e f l y illustrated
by c o n s i d e r a t i o n of the chamical p r o f i l e s derived f o r the area of
Koudhoorno The reference water which i n f i l t r a t e s
in the forested area upstream of Koudhoorn
i s , with the exception of K2 (fig~ 5c), not found at the sampling sites~ This imp l i e s t h a t the p o l l u t e d groundwater o r i g i n a t e s from the rural area of Koudhoorn. The great depths at which ~ o l l u t e d groundwater is found ( f i g s . 4 and 5b,c) and the relatively
small size of source area i n d i c a t e a deep recharge system f o r t h i s a r e a
The chemical p r o f i l e at K4 ( f i g .
5a) on the other hand, in the forested area
downstream of Koudhoorn, i n d i c a t e s a shallow i n f i l t r a t i o n
system. The unpolluted
112
reference water is here found to only 5 m below the groundwater table. The r e l a t i v e l y high concentrations of Cl-,SO~-,~ NOi , Na+, K+ and Ca2+ at greater depth suggest that the source area of t h i s water is located in the upstream rural area. I t is concluded that the chemical composition of groundwater in the studied areas is very heterogeneous. The v e r t i c a l v a r i a t i o n s in the groundwater composition r e f l e c t , on the regional scale, a t r a n s i t i o n between the reference water from f o r e s t and heath areas and polluted water from the rural centreso Concentrationincreases in the polluted water with respect to the reference water depend on the local differences in composition of i n f i l t r a t i n g
water. The d i s t r i b u t i o n of polluted
water from the source areas to a given depth in the studied p r o f i l e is governed by the local groundwater flow pattern, which in turn depends on the aquifer characteristics. ACKNOWLEDGEMENTS We thank T i n i B~er, Hetty de Liefde and Peter Overweg for t h e i r a n a l y t i c a l work, and Paul Smit f o r w r i t i n g the computer-program that plots the cumulative diagrams. The M i n i s t e r i e van Volksgezondheid and Milieuhygi~ne ( M i n i s t r y of Health & Environmental Protection) f i n a n c i a l l y supports this studY. REFERENCES I CoR~ Meinardi, RID Med~ 74-4, Nat° Insto for Water Supply, Voorburg, 1974, ppo 1-48. 2 CoR. Meinardi, RID Med. 78-4, Nat. Insto f o r Water Supply, Voorburg, 1978, ppo 1-50. 3 C. Ploegman, Landbouwko T i j d s c h r o / p t 86-7, (1974) i - 3 . 4 CoA.Jo Appelo and PoMoHo Smit, submitted to H20 (1981). 5 L. Vasak, Basis rap. CWG, V r i j e U n i v e r s i t e i t Amsterdam, 1979, pp. 1-33.
105
THE SPATIAL DISTRIBUTION OF POLLUTED GROUNDWATER FROM RURAL CENTRES IN A RECHARGE AREA IN THE NETHERLANDS - THE VELUWE L. VASAK, G.J.W. KRAJENBRINK and C.A.J. APPELO Instituut
voor Aardwetenschappen, V r i j e U n i v e r s i t e i t
Amsterdam
ABSTRACT A t o p o g r a p h i c a l l y e l e v a t e d area of ice-pushed r i d g e s was s e l e c t e d f o r a study on groundwater chemical composition in r e l a t i o n
to the p o t e n t i a l
pollution
sources.
A groundwater sampling technique using small ceramic cups was adapted f o r t h i s study. This technique a l l o w s d e t a i l e d sampling in depth f o r each b o r e h o l e , even in areas w i t h deep groundwater l e v e l s . Results of the chemical analyses show g r e a t v a r i a t i o n s
in v e r t i c a l
of the i o n - c o n c e n t r a t i o n s in groundwater. These v a r i a t i o n s r e f l e c t
distribution
the d i f f e r e n c e s
in land use and are also shown to be a f u n c t i o n of the groundwater f l o w p a t t e r n s .
INTRODUCTION In May 1979 a hydrochemical study was s t a r t e d in the NW p a r t of the Veluwe in the province of G e l d e r l a n d . The purpose of t h i s study was to e v a l u a t e the q u a l i t y of groundwater as a f f e c t e d by f a c t o r s such as p r e c i p i t a t i o n t y p e , land use and in p a r t i c u l a r
composition, soil
the disposal of manure and use o f f e r t i l i s e r s ,
The N~J p a r t of the Veluwe is a r e g i o n where i n t e n s i v e c a t t l e - f a r m i n g
has been
p r a c t i s e d during the past 20 y e a r s . An ever i n c r e a s i n g p r o d u c t i o n of manure on the one hand and a lack o f space on the o t h e r have r e s u l t e d in the d i s p o s a l of excessive a m o u ~ s o f manure on small areas. Under c e r t a i n h y d r o g e o l o g i c a l and biochemical c o n d i t i o n s , some manure and fertiliser
compounds may reach the s a t u r a t e d zone and hence p o l l u t e the ground-
w a t e r . Good q u a l i t y o f groundwater is e s s e n t i a l in the Veluwe, since i t
is an
i m p o r t a n t recharge area f o r d r i n k i n g water s u p p l i e s . STUDY AREA The Veluwe is a t o p o g r a p h i c a l l y e l e v a t e d area of ice-pushed r i d g e s bordered in the west and east by two v a l l e y s , p e c t i v e l y (see f i g .
the Gelderse V a l l e y and the IJssel V a l l e y res-
I).
0 0 4 8 - 9 6 9 7 / 8 1 / 0 0 0 0 - - 3 0 0 0 / $ 0 2 . 7 5 © 1981 Elsevier Scientific Publishing C o m p a n y
106
t
Drn i
(after
Fig~ 1o
N e l n a r d l f l 974
~¢
0
5I
110 km
Location of the study area~
Geological structure of the Veluwe is rather complex. The subsurface preglacial Pleistocene sediments consist of marine and f l u v i a l sands and clays° During the Saalian (= Riss-lce Age), the older Pleistocene sediments were pushed and new, g l a c i a l (boulder clay) and g l a c i o f l u v i a l (sand, gravel and clay) sediments were l a i d down° Aeolian sands formed during the l a s t Ice Age in Weichselian times (= WUrm) cover these ice-pushed ridges. Two main soil types can be distinguished in the Veluwe : podzolic and noncalcareous sand-soilso In the areas surrounding old rural centres mineral rich s o i l s were developed as a r e s u l t of human a c t i v i t i e s (long term manuring). The Veluwe is a recharge area with a mean annual p r e c i p i t a t i o n of 840 mm and an estimated evapotranspiration of 470 mm ( r e f . i ) . The i n f i l t r a t i n g
precipitation
excess is d i s t r i b u t e d by groundwater flow to the lower ly in g areas surrounding the Veluwe ( r e f . 2). The most important aquifer consists of Pleistocene sands and gravels with varying k-values (mean value + 60 m/day), l a i d down before and during the R i s s - g l a c i a t i o n . This a q u i fe r is up to 200 m thick and i t s base is formed by impervious Early Pleistocene marine clays° At locations where f l u v i a l and g l a c i o f l u v i a l clays occur, two or more aquifers can be distinguished. In the higher parts of the Veluwe, depths to groundwater exceed 25 m. Groundwater levels can be l o c a l l y effected by pumping stations~ A large part of the Veluwe region is covered by f o r e s t and heath which are source
areas of good q u a l i t y groundwater. The remaining c u l t i v a t e d areas consist
mainly of grassland and arable land with corn, beet and potato f i e l d s . The p o l l u t i o n sources in these areas may cause contamination of deep groundwater, due to the high permeability of the sediments, the aerobic conditions, and absence of organic matter w i t h i n the aquifer°
107 METHODS AND MATERIALS P r e l i m i n a r y e v a l u a t i o n of the h y d r o g e o l o g i c a l and chemical data obtained from e x i s t i n g w e l l s in the NW Veluwe led to the s e l e c t i o n of two small areas f o r more d e t a i l e d study, The l o c a t i o n s of these areas are shown in ~ig. 2. I
Fig. 2.
Sampling s i t e s and groundwater f l o w in the Koudhoorn and Garderen areas.
Both areas can be c h a r a c t e r i z e d as r u r a l centres w i t h i n t e n s i v e c a t t l e
farming
A b r i e f d e s c r i p t i o n of the two areas is given in t a b l e I . TABLE i C h a r a c t e r i s t i c s o f the s t u d i e d areas Location Garderen Koudhoorn
Elevation (m+m.s.l.)
Mean depth to g,w.(m)
Farm land area (ha)
35 - 45 20 - 30
20 11
380 100
Grass/arable land r a t i o 4 : I 9 : i
Manure prod. (ton N / y r . ) 83.23 17.23
Ene groundwater f l o w p a t t e r n in both areas is complex due to non-honlogeneity of the a q u i f e r . To the west (downstream) of Koudhoorn the f l o w is also a f f e c t e d by a pumping s t a t i o n (see f i g .
2).
In these two areas 11 borings were c a r r i e d out to depth which v a r i e d from 13 to 75 m, Locations o f the seven b o r i n g s i t e s discussed in t h i s paper are shown in f i g .
2. One b o r i n g is s i t u a t e d in the f o r e s t and the remainder are located in •
/
or immediately a d j a c e n t to farm land. Porous ceramic cups, commonly used in s o i l m o i s t u r e studies ( r e f .
3 ) , were
adapted f o r the groundwater sampling programme. This technique allows d e t a i l e d sampling in depth f o r each borehole even in a s i t u a t i o n w i t h deep groundwater l e v e l s ( , 8 m). C o n s t r u c t i o n d e t a i l s of the ceramic cup device are schematized in f i g .
3.
The groundwater samples were analyzed a t the I n s t i t u t e
of Earth Sciences
l a b o r a t o r y in Amsterdam. Nitrogen compound c o n c e n t r a t i o n s (NO3, NO2 and NH~) were determined on a Technicon A u t o a n a l y z e r , HCO and Cl
c o n c e n t r a t i o n s were
108 log
G2
o~ 5~
Lithology ~fine
r~
..... ~coarse
~o~ 15q
sand
!!ii
0
sand
~grevel Ioern
[]~]
g i?
20q
-I-ground
water
level
25q
30-I
'::i
354 ~ ceramic
'~:
pVC pipe ( ¢ 16 mill) (reservoir)
cups
see detail ~
404
45-4
~
5O J
Fig° 3.
screen
(~ 2 8 m m )
Construction details of the ceramic cup device for sampling uf deep groundwater° obtained by t i t r a t i o n ,
I~8~
~H4
~27
~L
,
. . . . . .
~.
c~
•
<
. . . .
,~
cL . o 3
turbidiometrical
~o4 No3
.
,
.
SO
by a
procedure, and
PO~- ions were determined c o l o r i -
,
,.o
metrically. A flame spectrometer
3~7~ r,
was used for the K+ analyses. All other cations were determined by ICP-emission spectrometry. Re-
,6
sults of the analyses are stored on magnetic tape for further processing ( r e f . 4)°
/
?
Cumulative diagrams are used here ?
for presentation of the analyses reL?
sults. In these diagrams, the con-
~ : ' ,'3
centrations of major ions (in meq/l) 3~
3S
are added and plotted against depth of sample (see f i g . 4).
3" 38
r
J
5~
41
4t
Fig° 4
Cumulative diagram showing ion-concentration variations with depth.
109
i¸
%,-
, •
i.
S I
:
I1:
| | I I I I I l I II I II ~ I I I
'~'"f7
--~
I I I II]]
lillillill
[i
3
] | l l l l l l , . , , , , , l l l , . , , ,
N K ..............................................................................
F
i~
. :~i~
"
0 0 ~q
.
0
p
;5
| O
/
4~
lllllllllllllllllllllli,,~lllllll
IIIIIIIIIliillltl,,,,,ll
~4~
¸
£
....
:
.
i ¸ 4~
i
i i i ~,iiii
i i
rc~
O
(D
O
t)
| - -
....
A
~,,,[~tttttlllllllllllll
,a I t i l l l l l l l l l l l l l l l l l l l t ~ i l l ~ t
G" O ~D
~
,zl
:'k -, •
~-~ ~!~.
, Lx~
cJ-
-
Ii0 RESULTS AND DISCUSSION Meinardi ( r e f . I) found that chemical composition of reference (unpolluted) groundwater from the Veluwe region is s i m i l a r to that f o r rain water, m u l t i p l i e d by an evapotranspiration f a c t o r . This evapotranspiration f a c t o r , which depends on the vegetation cover, was estimated to be 2.2 and i t s use results in estimated concentrations in the annual p r e c i p i t a t i o n excess given below :
CI-
SO#[ HC03 NO3
9
I0
6
1
Na+
Mg2+
Ca2+
NHZ
7
2.5
3.5
1
(mg/l)
*may have changed in recent years Similar concentrations, with the exception of Ca2+ and HC03 ions, are commonly found in the deep groundwater beneath the whole Veluwe region ( r e f . i ) and in upper parts of the a q u i f e r in the heath and f o r e s t areas ( r e f . 5). The concentrations of Ca2+ and HC03 ions are greater (up to 50 and 150 mg/l respectively) due to s o l u t i o n of CaCO3 from the aquifer sediments. Concentrations of the other ions are more or less uniform over the whole Veluwe, since the aquifer consists princ i p a l l y of sands containing up to 98 % unreactive quartz. Due this unique s i t u a t i o n a p o l l u t i o n index of groundwater is r e a d i l y defined : any substantial increase of the above ion concentrations can be considered as pollution. Variations in ion concentrations with depth at the seven sampling sites are shown in f i g s . 4 and 5o The water q u a l i t y which is s i m i l a r to that f or the reference water is indicated by arrows. I t can be seen that this reference water q u a l i t y is e i t h e r absent or is present in only a minor part of the studied p r o f i l e . A l l chemical p r o f i l e s show great v a r i a t i o n s of TDS concentrations with depth and the concentrations of i n d i v i d u a l ions can increase or decrease r a p i d l y (within I m). Table 2 shows the minimum and maximum concentrations of major ions (in mg/l) at the seven sampling sites in Koudhoorn and Garderen. TABLE 2 Minimum and maximum concentrations (mg/l) of major ions at the sampling sites in Koudhoorn (K) and Garderen (G) Sample Site
~Jmho 's/cm EC min.
mg/l M g ++
Ca ~ ~
max.
min.
max.
550
l.l
15.7
c~-
Na+
K+
~o~
.c%
mil~. max.
min.
max.
min.
max.
min.
max.
min
17.9
40.1
0.6
16.3
6.2
I,I.6
19.4
,I,I.6
17.6
83.1
2
32
i,I
63
8.5
15
10
0.5
[
248
8
47
26.2
1
183
11
58
16.1
I
188
160
9
69
1.1
i
2,17
K2
155
K3
210
725
3.9
17.4
11.0
86.6
3.9
33.0
6.1
25.3
12,8
37.9
20.0
K4
160
48O
i.I
7,7
17.6
57.7
O,S
6,5
4.7
21.2
9.7
36.1
16,8
K6
280
1050
3.2
12.4
40.5
156
6.8
9.9
8.2
39.2
26.6
55.7
38.,1
GI
520
850
3.8
11.4
71.7
i18
I.I
2.7
11,7
32.,I
G2
32O
870
3.8
II.0
41.3
131
1.2
8.7
11.4
28.7
20,0
65.2
G3
195
820
i,i
13.1
2,1.9
105
0,6
6.1
7.1
18.4
13..I
34. 1
106 ,
166 82.2
max.
~o~
max.
min.
min
f
1.0
max 163
156 57. 248
111
The concentrations of K+, Na+, Mg2+, C l - , SO~~ and NO~ can be many times g r e a t e r than those c a l c u l a t e d f o r the reference water. The maximum NO3 c o n c e n t r a t i o n exceeds 50 mg/l at a l l sampling s i t e s ,
t h i s value being the upper l i m i t
recommended
f o r d r i n k i n g water purposes. The peak c o n c e n t r a t i o n of 248 mg/l was found at sampling s i t e K6, immediately below the groundwater t a b l e . However, n i t r a t e concentrations of more than 100 mg/l have also been recorded at depths which are considerably below the groundwater t a b l e . For example : s i t e K3 : 143 mg/l at 34 m below groundwater t a b l e (43 m below the surface) K6 : 104 mg/l "
17 m
.
.
.
.
.
.
(30 m
. . . . . .
)
G2 : 125 mg/l "
14 m
.
.
.
.
.
.
(38 m
. . . . . .
)
There are three p o t e n t i a l p o l l u t i o n - s o u r c e s in the studied areas : - manure production from the i n t e n s i v e c a t t l e farming - use of f e r t i l i s e r s -
domestic sewage ( i n c l u d i n g the camping grounds). Data on the use of f e r t i l i s e r s
have not y e t been obtained° The two other sources
can be q u a n t i f i e d approximately on the basis of i n h a b i t a n t e q u i v a l e n t numbers ( i . e ~ ) : manure production : domestic sewage
:
Koudhoorn
Garderen
7°858
51~143
952
2~350
These f i g u r e s i n d i c a t e t h a t manure production can be considered as the main source of p o l l u t i o n in Koudhoorn and Garderen when compared with the output of domestic sewage~ The composition of i n f i l t r a t i n g
water in the manured farming areas is determined
by the manure type (from cows, calves, pigs and p o u l t r y ) , the q u a n t i t y of manure transported to the land, the period of manuring and by the crop cover and s o i l type. The t r a n s p o r t of p o l l u t e d water in the saturated zone depends on hydrogeological c h a r a c t e r i s t i c s of the studied area~ Despite the f a c t t h a t the hydrogeological s i t u a t i o n is in a general sense known, the l o c a l f l o w patterns are poorly defined~ Consequently, the d e t a i l e d r e l a t i o n s h i p s between the h o r i z o n t a l v a r i a t i o n s in land use and the v e r t i c a l
v a r i a t i o n s in the composition of groundwater have not y e t been
determined in the present study phase° The complex s i t u a t i o n may be b r i e f l y illustrated
by c o n s i d e r a t i o n of the chamical p r o f i l e s derived f o r the area of
Koudhoorno The reference water which i n f i l t r a t e s
in the forested area upstream of Koudhoorn
i s , with the exception of K2 (fig~ 5c), not found at the sampling sites~ This imp l i e s t h a t the p o l l u t e d groundwater o r i g i n a t e s from the rural area of Koudhoorn. The great depths at which ~ o l l u t e d groundwater is found ( f i g s . 4 and 5b,c) and the relatively
small size of source area i n d i c a t e a deep recharge system f o r t h i s a r e a
The chemical p r o f i l e at K4 ( f i g .
5a) on the other hand, in the forested area
downstream of Koudhoorn, i n d i c a t e s a shallow i n f i l t r a t i o n
system. The unpolluted
112
reference water is here found to only 5 m below the groundwater table. The r e l a t i v e l y high concentrations of Cl-,SO~-,~ NOi , Na+, K+ and Ca2+ at greater depth suggest that the source area of t h i s water is located in the upstream rural area. I t is concluded that the chemical composition of groundwater in the studied areas is very heterogeneous. The v e r t i c a l v a r i a t i o n s in the groundwater composition r e f l e c t , on the regional scale, a t r a n s i t i o n between the reference water from f o r e s t and heath areas and polluted water from the rural centreso Concentrationincreases in the polluted water with respect to the reference water depend on the local differences in composition of i n f i l t r a t i n g
water. The d i s t r i b u t i o n of polluted
water from the source areas to a given depth in the studied p r o f i l e is governed by the local groundwater flow pattern, which in turn depends on the aquifer characteristics. ACKNOWLEDGEMENTS We thank T i n i B~er, Hetty de Liefde and Peter Overweg for t h e i r a n a l y t i c a l work, and Paul Smit f o r w r i t i n g the computer-program that plots the cumulative diagrams. The M i n i s t e r i e van Volksgezondheid and Milieuhygi~ne ( M i n i s t r y of Health & Environmental Protection) f i n a n c i a l l y supports this studY. REFERENCES I CoR~ Meinardi, RID Med~ 74-4, Nat° Insto for Water Supply, Voorburg, 1974, ppo 1-48. 2 CoR. Meinardi, RID Med. 78-4, Nat. Insto f o r Water Supply, Voorburg, 1978, ppo 1-50. 3 C. Ploegman, Landbouwko T i j d s c h r o / p t 86-7, (1974) i - 3 . 4 CoA.Jo Appelo and PoMoHo Smit, submitted to H20 (1981). 5 L. Vasak, Basis rap. CWG, V r i j e U n i v e r s i t e i t Amsterdam, 1979, pp. 1-33.