The pumping test 'De Vennebulten' which will be described in this report forms part of a large-scale groundwater exploration in the 'Achterhoek' region, province of Gelderland. In greater parts of this region, covering some 100 000 ha, groundwater is pumped from Young Pleistocene formations underlain by almost impervious layers of Tertiary clay and clay-bearing fine sands

Ridder, N.A., de

Name not available

Analysis of the pumping test "De Vennebulten" near Varsseveld

Wageningen Yield 

BIBLIOTHEEK 
NN31545.0335 STARINGGEBOUW 
«INSTITUUT VOOR CULTUURTECHNIEK EN WATERHUISHOUDING 
% 
NOTA 335, d.d. 20 april 1966 
Analysis of the pumping test 'De Vennebulten' 
near Varsseveld 
N. A. de Ridder 
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1 1 FEB. 1998 
- 1 -
Introduction 
The pumping test 'De Vennebulten' which will be described in this 
report forms part of a large-scale groundwater exploration in the 'Achter-
hoek' region, province of Gelderland. In greater parts of this region, 
covering some 100 000 ha, groundwater is pumped from Young Pleistocene 
formations under'laiii by almost impervious layers of Tertiary clay and 
clay-bearing fine sands. These water-bearing materials consist chiefly 
of fluvioglacial deposits and Rhine sediments, varying in thickness from 
some 10 m to more than 50 m. In the eastern part of the region, however, 
water-bearing layers are absent or very thin and the impervious Tertiary 
(Oligocène, Miocene) formations are found at the surface or at shallow 
depth. 
The pumping test site is located between the villages of Varsseveld 
and Lichtenvoorde (fig. 1). The Water Supply Company 'Oostelijk Gelder-
land' carriedomt some exploration wells at this place. Before groundwater 
resources can be managed they must be quantitatively appraised. For this 
purpose the Institute for Land and Water Management Research at Wageningen 
carried out a pumping test which will be described hereafter. 
Scheme of the test 
Besides a pumping well, four observation wells were made at distances 
of 10, 30, 90 and 280 m from the pumping well (fig. 2). As can be seen in 
this figure the aquifer was found at a depth of approximately 10 to 21 m 
below the surface. It is composed of gravel-bearing coarse and very coarse 
sands and its thickness is 11m. The aquifer is underlain by almost im-
pervious marine clays of Middle Miocene age (impervious basis layer) and 
on its top fine and very fine sands are present with a thickness of about 
10 m. A part of this covering layer consists of loamy sand. 
A pumping screen of 11 m length and 3" diameter made of polyvinyl 
chloride (P.V.C,)., was installed over the full thickness of the aquifer 
(so-called fully penetrating well). In the observation wells at 10, 30, 
90 and 280 m distance small filters with a length of 1 m and a diameter 
of 1" were installed somewhere in the middle of the aquifer, Near each well 
217 

» 
1 
- 2 -
also a shallow observation well was made in which a filter at a depth of 
3 to 4 m w a s installed. Measuring data from these shallow wells permit to 
determine whether the groundwater in the underlying aquifer is confined, 
semi-confined or phreatic. 
Prior to the test the water levels in the various wells were measured 
regularly during 10 days. This was done to determine whether or not a 
correction of the drawdowns during the test had to be made. As a result 
of the drainage the water table may fall several millimeters per hour 
and this has to be accounted for in the analysis of the test data. One 
day after the test the water levels in all wells were also measured. 
Pumping was started at 10 27 on October 28, 1965 and was continued 
for a period of about 25,5 hours at a constant rate of 36.37 m /hour 
until 11 59 on October 29. When pumping stopped the rise of the water 
levels was measured during about 5 hours (recovery test). The water pumped 
during the test was discharged through a closed pipe to a ditch in order 
to prevent any recharge of the tested aquifer. 
Analysis of the test data 
To analyze the pumping test data drawdowns in the deep observation 
wells W II 10, W II 30, W II 90 and W II 280 were plotted on semi-logarith-
mic paper against the time. These so-called time-drawdown curves are shown 
in figure 3« As can be seen in this figure the curves start to run parallel 
after 4-0 to 50 minutes of pumping and at the end of the test drawdowns 
become very small which indicates that stationary flow conditions (stage 
of equilibrium) had almost been reached. From this type of curves it can 
be concluded that the tested aquifer is a leaky aquifer and the groundwater 
is semi-confined. This means that during pumping not only water was with-
drawn from the tested aquifer but also from the overlying fine sand and 
loamy sand layer. Figure 4, showing the time-drawdown curves of the shallow 
observation wells (drawn on linear scale) and figure 5 presenting the 
maximum drawdowns in all wells measured at the end of the pumping period 
provide evidence for this statement. When the tested aquifer was a confined 
aquifer no drawdown in the shallow observation wells would have been mea-
sured. Under phreatic groundwater conditions drawdowns in the shallow and 
deep filters of a certain observation well would have been the same. 
Since we have to deal with a leaky or semi-confined aquifer the method 
217 

- 3 -
of DE GLEE will be applied for calculation of the geohydrologic characte-
ristics. In 193O DE GLEE derived the following equation 
« ^ ' 2^kD Ko $ ) 
where 
Ç(r) is the maximum stabilized drawdown (in m) in an observation well at 
a distance r(in m) from the pumping well 
Q is the discharge of the pumped well (in m /day) 
kD is the transmissibility of the aquifer (in m /day) 
K is a modified Bessel function of the 2nd kind and of zero order, 
o 
^ = Vk;D.c is the leakage factor (in m) 
1 
c = — is the hydraulic resistance or leakage coefficient of the semi-
v - pervious covering layer (in days) 
D is the thickness of the saturated part of this layer(in m) and 
k is the vertical hydraulic conductivity of this layer (in m/days). 
To calculate the values of kD and c the procedure is as follows: 
Th£$ distance-drawdown curve is constructed on double logarithmic paper by 
plotting the maximum stabilized drawdown (in m) of each deep observation 
well.against the distance (in m)of this well to the pumped well. 
À second sheet of logarithmic paper with the same scale is used for 
the construction of the type curve (K (x) versus x). The values of K (x) 
for a wide range of x are found in textbooks. The observed field data curve 
is now superimposed on the type curve, keeping the coordinate axes of the 
two curves parallel and adjusted until a position is found where the field 
data curve fall on the type curve (fig.6). The cross mark of the type curve 
sheet is then indicated on the field data sheet. 
0. The vertical displacement of the axis stands for the quotient
 pI.' ' 
from which kD can be derived. The horizontal displacement of the axis 
stands for the leakage factor A = VkD.c, from which the hydraulic resis-
tance c can be calculated. 
For the vertical displacement 0.08 m is found 
ll'J.Lïviï - °-08 k D = I745m2/day 2x3.14xkD 
217 
- 4 -
The horizontal displacement is 1000 m 
VkD.c = 1000 m c = 570 days 
Taking into account the thickness of the aquifer and the covering layer 
it can be found that the average hydraulic conductivity of the aquifer for 
horizontal flow k-^^160 m/day and that of the semi-pervious covering 
layer for vertical flow k ^0.017 m/day. 
It should be noted that DE GLEE's method of solution is based on the 
assumption that the leakage through the covering layer is proportional 
to the drawdown in the aquifer. Above the semi-pervious layer phreatic 
water with a constant level is assumed to exist. Since some drawdown of 
the phreatic water level occurred during the test this condition is not 
satisfied (figures 4 a^d 5) an(i an error in the obtained results may be 
expected. 
The condition of a constant phreatic water table would have been sa-
tisfied if the drawdowns in all observation wells were some 12 to 18 cm 
smaller. Subtracting of this amount from the measured drawdowns at the end 
of the test and applying then DE GLEE'S method of solution yield similar 
results for kD, but a substantial smaller value for c, namely 23 days 
(see dashed curves in fig. 6). This result seems to be more reasonable 
than the forementioned relatively high value of 570 days. 
Figure 3 shows that 40 to 50 minutes after the pump started the dif-
ference in drawdown between the various wells became-constant. We can 
therefore apply the Thiem formula 
2FkD(h.- O 
Q = — J -
In r2/r1 
Application of this formula for the wells W Il/10 and W II/30 gives 
8?2.9 , 6.28 kB x O.O75 k D . 2041 ra2/day 
In ^ '10 
For the wells W II/30 and W II/90 
„ „ c 6.28 kD x 0.105 , « ..cc 2/, 
872.9 = QX L kD = 1455 m /day 
In 90/30 
217 
- 5 -
For the wells W II/90 and W 11/280 
872.9 - 6- 2 8 k B " ° - 0 9 M> - 1753 m2/aay 
In 280/90 
It appears that the transmissibility varies from one place to another. 
The average of these three values is 1750 m /day which is in agreement 
with the result obtained by applying the method of DE GLEE. 
To answer the question whether or not the time-drawdown curves of 
figure 3 have to be corrected for changes of the water tables not caused 
by pumping, figure 7 w a s drawn. This figure shows that during the pumping 
period a certain drop of the water table must have taken place due to 
drainage. However, this drop of the water table was so small that it may 
be neglected. 
From figure 8 it could be concluded that during the pumping period 
the drop of the phreatic water level was larger than that of the water 
level in the aquifer what seems unrealistic. The observation data of the 
day after the test cannot be used because it is assumed that the phreatic 
water level was not yet fully re-established at that time. 
Finally, it should be noted that application of the Thiem formula 
for a leaky aquifer is not allowed unless the discharge (P) of the pumped 
well is corrected. Strictly taken, the amount of water delivered by the. . 
semi-pervious covering layer should be determined. This quantity has to be 
subtracted from the well discharge (Q,), resulting in a somewhat lower value 
of kD. In the present case this correction is difficult to perform due to 
insufficient data. On the other hand such a correction seems hardly neces-
sary because the calculated value of kD is on the average in good agreement 
with that obtained by applying DE GLEE's method of solution. 
In summary it can be stated that the transmissibility of the aquifer 
has the order ' ôï••'îH«gMlit'ti•dé', of l^'^ m-/day < -T-he*'hydraulic- resistance-o-f—the 
semi-pervious covering layer is approximately 20 to 25 days, from which 
can be derived that the vertical hydraulic conductivity of this layer is on 
the average 0.5 m/day. 
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Pumping test "De Vennebulten" 
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Groundwater tables in the shallow observation 
wells before and after pumping 
Pumping test "De Vennebulten" 
fig. 8 
125r-
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1 2 7 -
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1 8 5 -
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1.4 cm 
.Wn 90 Lb.b. 
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kWii30 Lb.b. 
drainage 0.54 mm /h 
= 0.90 mm/100 min 
drainage 0.94mm/h 
= 1.57 mm/100min 
1.2 cm 
WE 10 l.b.b. 
drainage 0.47 mm/h 
= 0.78 mm/100min 
i 
26/10 27/10 28/10 29/10 30/10 
66C 563/2.7 


Analysis of the pumping test "De Vennebulten" near Varsseveld

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