Procedure for conducting pumping tests

1
PROCEDURE FOR CONDUCTING
PUMPING TESTS
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth
Science,
University of Mysore, Mysore

2
Objective:
Pumping Tests are conducted to examine the
aquifer response, under controlled conditions, to
the abstraction of water.
Hydrogeologists determine the hydraulic
characteristics of water-bearing formations, by
conducting pumping tests.

3
A pumping test is a practical, reliable method of
estimating well performance, well yield, the
zone of influence of the well and aquifer
characteristics. There is a procedure for
conducting pumping tests in wells. This lesson
highlights the prevailing methods adopted while
conducting pumping tests.

4
Introduction:
Hydrogeologists determine the hydraulic
characteristics of water-bearing formations, by
conducting pumping tests. Pumping Test is
conducted to examine the aquifer response,
under controlled conditions, to the abstraction
of water.

5
The basic principle of a pumping test is that if
we pump water from a well and measure the
pumping rate and the drawdown in the well
then we can substitute these measurements into
an appropriate formula and can calculate the
hydraulic characteristics of the aquifer.
It is also called as aquifer tests for aquifer
parameter evaluation.

6
Groundwater is frequently chosen as the most
suitable source of drinking water, supplies of
which are brought to the surface by
rehabilitating existing boreholes or drilling new
ones. Pumping tests are a practical way of
obtaining an idea of the borehole’s efficiency
and its optimal production yield.

7
What is a pumping test ?
A pumping test consists of pumping
groundwater from a well, usually at a constant
rate, and measuring water levels in the pumped
well and any nearby wells (observation wells)
or surface water bodies during and after
pumping.

8
A pumping test is a practical, reliable method of
estimating well performance, well yield, the
zone of influence of the well and aquifer
characteristics (i.e., the aquifer’s ability to store
and transmit water, aquifer extent, presence of
boundary conditions and possible hydraulic
connection to surface water).

9
Aquifer test and aquifer performance
test (APT) are alternate designations for a
pumping test. In petroleum engineering, a
pumping test is referred to as a drawdown test.
Purpose of conducting Aquifer Tests:
Hydrogeological studies include determination
of aquifer parameters by conducting pumping
tests on dug / bore / tube wells and analysis of
pumping test data.

10
Basically, pumping tests are conducted for a
wide variety of reasons, including the
following:
a) To determine the reliable long-term yield
(or ‘safe’ yield) of a borehole.
b) To assess the hydraulic performance of a
borehole, usually in terms of its yield-
drawdown characteristics. How much

11
drawdown does it take to yield a certain
amount of water?
c) To derive the hydraulic properties of the
aquifer.
d) Pumping tests are the classic (and perhaps
the only) way to derive in situ aquifer
hydraulic properties, such as transmissivity
and the storage coefficient, or to reveal the
presence of any hydraulic boundaries.

12
e) To test the operation of the pumping and
monitoring equipment,
f) To determine the effects of abstraction on
neighbouring abstractions (sometimes
referred to as derogation).
g) To determine the environmental impact of
the abstraction.
h) To provide information on water quality. Is
the water quality suitable for the intended
use?

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i) Are there likely to be any problems such as
drawing in saline or polluted water after
extended periods of pumping?
j) To optimize operational pumping regimes.
k) To help determine the correct depth at
which the permanent pump should be
installed in the borehole.

14
Important aquifer parameters:
Porosity : measure of void space in the rock
formations. It is defined in percentage as the
ratio of the void pore space to the total volume
of the rock formation sampled.
Hydraulic conductivity : rate of flow under a
unit hydraulic gradient through a unit cross-
sectional area of aquifer. The unit is in m/ day.

15
Transmissivity :
It is the rate of flow of groundwater under a unit
hydraulic gradient through an aquifer of unit
width and unit thickness.
That is, transmissivity is the product of
hydraulic conductivity and thickness of the
aquifer.
The unit is in m2
/day.

16
Storativity or storage coefficient, applicable
for confined aquifers :
It is the volume of water released from storage
per unit surface area of a confined aquifer per
unit decline in hydraulic head.
It is dimensionless.

17
Specific yield, applicable for unconfined
aquifers :
It is the volume of water released from storage
under gravity by an unconfined aquifer per unit
surface area of aquifer per unit decline of the
water table.
The Specific yield is dimensionless or can be
given in %.

18
Specific capacity of a well :
It is the ratio of discharge of the well to the
drawdown, in m3
/hour/m.
The objectives of the pumping test are to
determine well yield, determine well
efficiency, determine aquifer parameters and to
examine water chemistry.

19
Pump testing is a major investigative tool.
It requires proper planning, observations, and
method of interpretation of data.
It is cheaper (much) if existing wells can be
used.
Pumping test is carried out in newly constructed
wells.
The distance should not be far off.

20
Technical terms related to pumping tests are:
The well used for pumping is called as pumping
well or exploratory well.
The water level of the same well may be used.
Otherwise, some nearby well may be used as an
observation well.
The water level observed in a well is called as
hydraulic head.

21
A well yield test is a short (e.g., approximately
one hour) flow test, usually done by a qualified
well driller once the well is completed to
provide a rough estimate of the well’s yield.
It is generally recorded in the well construction
report by the driller.
Well yield tests are done using bailing1 or air
lifting methods.

22
Well yield is a measure how much water can be
withdrawn from the well over a period of time
and measured in m3/hr or m3/day.
Specific capacity is referring to whether the
well will provide an adequate water supply.
Specific capacity is calculated by dividing
pumping rate over drawdown (Q/S).
The Static water level is the level of water in
the well when no water is being taken out.

23
Dynamic Water level is the level when water is
being drawn from the well.
The cone of depression occurs during pumping
when water flows from all directions toward the
pump.
The term Drawdown refers to the declining
water level in a well due to pumping.

24
Common types of pumping tests
The common types of pumping tests conducted
include the following:
Constant-rate tests:
In this test it is necessary to maintain pumping
at the control well at a constant rate. This is the
most commonly used pumping test method for
obtaining estimates of aquifer properties.

25
These tests are carried out by pumping at a
constant rate for a much longer period of time
than the step test, and primarily designed to
provide information on the hydraulic
characteristics of the aquifer.
Information on the aquifer storage coefficient
can be deduced only if data are available from
suitable observation boreholes.

26
Step-drawdown tests :
These tests proceed through a sequence of
constant-rate steps at the control well to
determine well performance characteristics such
as well loss and well efficiency. Step tests are
designed to establish the short-term relationship
between yield and drawdown for the borehole
being tested.

27
It consists of pumping the borehole in a series
of steps, each at a different discharge rate,
usually with the rate increasing with each step.
The final step should approach the estimated
maximum yield of the borehole
Recovery tests :
These tests use water-level (residual drawdown)
measurements after the termination of pumping.

28
Although often interpreted separately, a
recovery test is an integral part of any pumping
test.
Recovery test are carried out by monitoring the
recovery of water levels on cessation of
pumping at the end of a constant-rate test (and
sometimes after a step test).

29
It provides a useful check on the aquifer
characteristics derived from the other tests but
is valid only if a foot-valve is fitted to the rising
main; otherwise water surges back into the
borehole.
Preliminary studies:
When planning a pumping test, it is useful to
gather together all the information that can be
found about the aquifer and the borehole itself.

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Basic geology:
Are the rocks crystalline basement, volcanic,
consolidated sediments or unconsolidated
sediments? Groundwater occurs in these rocks
in different ways, and behaves in different
ways.

31
Aquifer configuration:
Is the aquifer confined, unconfined or leaky?
Borehole construction:
How deep is the borehole, and of what
diameter?
Has solid casing, screen or gravel pack been
installed?

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Installed equipment:
If a pump is already installed in the borehole,
what are its type and capacity, and at what
depth is the pump’s intake? Can the pumping
rate be varied?
Historical or background water levels:
Information about the historical behaviour of
the groundwater level is very useful.

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Does the water level vary much from wet
season to dry season?
In the period before the test takes place, is the
water level already falling or rising or is it
stable? What is the current water level?
Local knowledge:
Residents often have a surprisingly good
understanding of how the groundwater in the
area behaves.

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For example, how does the water level respond
to rainfall?
Can borehole yields be maintained?
Is the water safe for drinking, and does the
water quality change over time?
Planning Stage:
Designing and planning a pumping test is
critical prior to testing.

36
Lack of planning can result in delays, increased
costs, technical difficulties and poor or unusable
data.
Some things to consider in the pre-planning
stage are:
a) time of year the pumping test should be
done
b) natural variations in the groundwater levels
that occur during the test
c) informing others who may be affected

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d) depth of pump setting and type of pump
e) pumping duration
f) pumping rate
g) control and measurement of the pumping
rate
h) frequency of measurements of the water
levels
i) measuring water levels in neighbouring
wells and/or streams
j) discharge of pumped water

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k) collection of water samples for water
quality analysis special conditions to be
aware of e.g., salt water intrusion in coastal
aquifers
Materials required for conducting pumping
tests:
For conducting pumping tests and analysing the
data, the following items may be required:
a) generator
b) submersible pump

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c) discharge pipe, connections
d) flow measurement device(s)
e) tape measure(s), steel tape(s) and
carpenter's chalk
f) pressure transducer(s), cables, data
logger(s)
g) electric water-level sounder(s) and
batteries
h) watches/stopwatches
i) barometric sensor/ thermometer

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j) pH and conductivity meters
k) sample bottles
l) toolkit, , wires
m) data collection forms, log book,
permanent-ink pens
n) computer, calculator
o) graph paper (semilog, log) and/or
computer software
p) references, standard operating procedures

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q) manufacturer's operating manuals for
equipment
r) maps (site, geologic and topographic),
cross section(s).
Well-Inventory analysis:
Well-inventory is one basic step. Well
inventories are also conducted as part of most of
the environmental investigations.

42
Different types of wells are studied for
recording their yielding capacities, main
aquifers contributing to yield, etc. The nature
and period of their use and sustainability are
also recorded. The hydrostatic heads of the
aquifers are monitored on a monthly basis
through shallow dugwells (monitoring stations),
piezometers, deep wells, etc, in the areas. Water
samples are collected from selected wells and

43
analysed to determine the variation of water
quality over time and space.
Before conducting a pumping test the
geological and hydrological information of the
area should be collected.
1. The geological characteristics of the
subsurface (i.e. all those lithological,
stratigraphic, and structural features that may
influence the flow of groundwater).

44
2. The type of aquifer and confining beds.
3.The thickness and lateral extent of the aquifer
and confining beds.
4. The aquifer may be bounded laterally by
barrier boundaries of impermeable material in
the lithology (e.g. the bedrock sides of a buried
valley, a fault, or simply lateral changes of the
aquifer material);

45
Data on the groundwater-flow system:
horizontal or vertical flow of groundwater,
water table gradients, and regional trends in
groundwater levels.
Details of any existing surrounding wells in the
area.
Selecting the well for the pumping tests:
Well should be suitable for the test.

46
The hydrogeological conditions should not
change over short distances and should be
representative of the area under consideration,
or at least a large part of it;
- The site should not be near railways or
motorways where passing trains or heavy
traffic might produce measurable fluctuations in
the hydraulic head of a confined aquifer;

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- The site should not be in the vicinity of
existing discharging wells;
- The pumped water should be discharged in a
way that prevents its return to the aquifer.
The gradient of the water table or piezometric
surface should be low;

48
Manpower and equipment must be able to
reach the site early and easily.
New Exploratory and observations wells:
If there is no existing well in a region, bore
wells are drilled for pumping test purpose.

49
Sometimes, bore well drilled for drinking water
supply purpose are tested to know the
hydrological properties, by conducting pumping
tests.
Well diameter:
Before conducting the pumping test the
dimensions of the well should be measures.

50
Radius for circular wells. length and width for
rectangular wells.
The depth also should be measured. if it is new
well, during the drilling operations, samples of
the geological formations that are pierced
should be collected and described lithologically.
Records should be kept of these lithological
descriptions, and the samples themselves should
be stored for possible future reference.

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Well screen: for bore wells, the casing pipe
length should be measured.
The pump : -
The pump and power unit should be capable of
operating continuously at a constant discharge
for a period of at least a few days.

52
There are several factors to be considered when
determining the type of pump to be used and
the depth at which it should be set, including:
a) well diameter and desired pumping rate
b) total dynamic head including the pumping
water level, the above ground head (if
applicable) and all friction losses in the casing,
pipes, fittings, etc.;
c) reliability of power source; and horsepower
requirements.

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An even longer period may be required for
unconfined or leaky aquifers, and especially for
fractured aquifers.
In such cases, pumping should continue for
several days more.
The capacity of the pump and the rate of
discharge should be high enough to produce
good measurable drawdowns in piezometers.

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It should be as far away as, say, 100 or 200 m
from the well, depending on the aquifer
conditions.
Discharging the pumped water:
The water delivered by the well should be
prevented from returning to the aquifer of the
same well.

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This can be done by conveying the water
through a large-diameter pipe, say over
a distance of 100 or 200 m, and then
discharging it into a canal or natural channel.
Piezometers:
Bore wells used to only measure the water
levels nearer to the pumping wells are called as
piezometers.

57
The water levels measured in piezometers
represent the average head of the nearby
aquifer. Piezometers should be placed not too
near the well, and not too far from it, also.
Depth of the piezometers:
The depth of the piezometers is at least as
important as their distance from the well.

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In an isotropic and homogeneous aquifer, the
piezometers should be placed at a depth that
coincides with that of half the length of the well
screen.
For example, if the well is fully penetrating and
its screen is between 10 and 20 m below the
ground surface, the piezometers should be
placed at a depth of about 15 m.

59
The type of aquifer:
When a confined aquifer is pumped, the loss of
hydraulic head propagates rapidly because the
release of water from storage is entirely due to
the compressibility of the aquifer material and
that of the water. The drawdown will be
measurable at great distances from the well, say
several hundred metres or more.

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In unconfined aquifers, the loss of head
propagates slowly.
Here, the release of water from storage is
mostly due to the dewatering of the zone.
A leaky aquifer occupies an intermediate
position.

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Transmissivity:
When the transmissivity of the aquifer is high,
the cone of depression induced by pumping will
be wide and flat .
When the transmissivity is low, the cone will be
steep and narrow.
In the first case, piezometers can be placed
farther from the well than they can in the
second.

62
The duration of the test:
The duration of the pumping test depends on the
purpose of the well, the type of aquifer and any
potential boundary conditions.
Theoretically, in an extensive aquifer, as long as
the flow to the well is unsteady, the cone of
depression will continue to expand as pumping
continues.

63
Therefore, for tests of long duration,
piezometers can be placed at greater distances
from the well than for tests of short duration.
The discharge rate :
During the aquifer test, discharge should be
measured accurately and frequently enough to
verify that a constant discharge rate is being
achieved. Waste of the discharge should be
avoided.

64
If the discharge rate is high, the cone of
depression will be wider and deeper than if the
discharge rate is low.
With a high discharge rate, therefore, the
piezometers can be placed at greater distances
from the well.
Control of the pumping rate:
Control of the pumping rate during the test is
important.

65
Because it allows for reliable drawdown data to
be collected to determine the yield of the well
and aquifer properties.
Controlling the pumping rate by adjusting the
pump speed is generally not satisfactory.
It is better to use a gate valve to adjust the
pumping rate to keep it constant.

66
The discharge pipe and the valve should be
sized so that the valve will be from ½ to ¾ open
when pumping at the desired rate.
The valve should be installed at a sufficient
distance from the flow measurement device to
avoid any impacts from turbulence.
Measuring the discharge of pumped water
accurately is also important and common
methods of measuring discharge include the use
of an orifice plate and manometer.

67
Aquifers with stratification:
Homogeneous aquifers are rare in nature. Most
of the aquifers are stratified to some extent.
Stratification causes differences in horizontal
and vertical hydraulic conductivity, so that the
drawdown observed at a certain distance from
the well may differ at different depths within
the aquifer. As pumping continues, these
differences in drawdown diminish.

68
Moreover, the greater the distance from the
well, the less effect stratification has upon the
drawdowns.
Fractured rock :
Deciding on the number and location of
piezometers in fractured rock poses a special
problem, although the rock can be so densely
fractured that its drawdown response to
pumping resembles that of an unconsolidated
homogeneous aquifer;

70
if so, the number and location of the
piezometers can be chosen in the same way as
for such an aquifer.
The measurements to be taken:
The measurements to be taken during a
pumping test are of two kinds:
- Measurements of the water levels in the well
and the piezometers.

71
- Measurements of the discharge rate of the
well.
Ideally, a pumping test should not start before
the natural changes in hydraulic head in the
aquifer are known
- both the long-term regional trends and the
short-term local variations.

72
So, for some days prior to the test, the water
levels in the well and the piezometers should be
measured, say twice a day.
Water-level measurements:
The water levels in the well and the piezometers
must be measured many times during a test, and
with as much accuracy as possible.

73
Because water levels are dropping fast during
the first one or two hours of the test, the
readings in this period should be made at brief
intervals.
As pumping continues, the intervals can be
gradually lengthened.
After the pump has been shut down, the water
levels in the well and the piezometers will start
to rise - rapidly in the first hour, but more
slowly afterwards.

74
These rises can be measured in what is known
as a recovery test.
Duration of the pumping test:
The question of how many hours to pump the
well in a pumping test is difficult to answer
because the period of pumping depends on the
type of aquifer and the degree of accuracy
desired in establishing its hydraulic
characteristics.

75
At the beginning of the test, the cone of
depression develops rapidly because the
pumped water is initially derived from the
aquifer storage immediately around the well.
Conversion of the data:
The water-level data collected before, during,
and after the test should first be expressed in
appropriate units.

77
The measurement units of the International
System are recommended, but there is no fixed
rule for the units in which the field data and
hydraulic characteristics should be expressed.
Transmissivity, for instance, can be expressed
in m2/s or m2/d.
Field data are often expressed in units other
than those in which the final results are
presented.

78
Time data, for instance, might be expressed in
seconds during the first minutes of the test,
minutes during the following hours, and actual
time later on, while water-level data might be
expressed in different units of length
appropriate to the timing of the observations.
It will be clear that before the field data can be
analyzed, they should first be converted: the

79
time data into a single set of time units (e.g.
minutes) and the drawdown data into a single
set of length units (e.g. metres), or any other
unit of length that is suitable.
Pump regime - General guidance:
For Confined aquifers:
Transmissivity is more important than
storativity:
observation wells are not always needed
(although accuracy lost without them!).

80
For Unconfined aquifers:
Storativity much larger, and has influence over
transmissivity estimates: observation wells
important as is larger test duration.
Care is needed if aquifer only partly screened.

81
Measurement intervals to be considered:
Water levels measurements for pumping well
could be taken as the following :
Time since start of
pumping
(minutes)
Time
intervals
(minutes)
0 – 5 0.5
5 – 60 5
60 – 120 20
120 – shut down the pump 60

82
Similarly, for observation wells, water level
measurement can be taken as the following:
Time since start of
pumping (minutes)
Time intervals
(minutes)
0 – 5 0.5
5 – 15 1
15 – 50 5
50 – 100 10
100 – 300 30
300 – 2,880 60
2,880 – shut down the pump 480

83
After the pump has been shut down, the water
levels in the well will start to rise again.
These rises can be measured in what is known
as recovery test.
If the pumping rate was not constant throughout
the pumping test, recovery-test data are more
reliable than drawdown data because the water
table recovers at a constant rate.

84
Measurements of recovery shall continue until
the aquifer has recovered to within 95% of its
pre-pumping water level.
Amongst the arrangements to be made for
pumping test is a discharge rate control. This
must be kept constant throughout the test and
measured at least once every hour, and any
necessary adjustments shall be made to keep it
constant.

85
Basic Assumptions :
We need to make assumptions about the
hydraulic conditions in the aquifer and about
the pumping and observation wells. All
geological formations are horizontal and of
infinite horizontal extent.
The potentiometric surface of the aquifer is
horizontal prior to the start of the pumping.

86
The potentiometric surface of the aquifer is not
changing with time prior to the start of the
pumping.
All changes in the position of the potentiometric
surface are due to the effect of the pumping
well alone. The aquifer is homogeneous and
isotropic. All flow is radial toward the well.
Groundwater flow is horizontal. Darcy’s law is
valid. Groundwater has a constant density and
viscosity.

87
Proper discharge of the pumped water:
Proper discharge of the pumped water is
important to ensure there is no damage due to
erosion, flooding or sediment deposits in
streams.
For land disposal, direct the water from the
pumping well in a down-hill direction at a
sufficient distance from the pumping well.

88
This will prevent re-circulation of the pumped
water into the well or aquifer and will preserve
both the pumping water level and the integrity
of the pumping test.
Collecting water samples for analysis:
A pumping test is a good time to collect water
quality samples to assess the chemical, physical
and bacterial properties of the water.

89
Water samples should be collected when
conditions have stabilized.
Hydrofracturing :
If hydrofracturing (fracking) has been used to
increase the productivity of the well, it may
advisable to wait up to a week before
conducting the pumping test.

90
Pumping Test Report:
The formal report for a pumping test should be
submitted at the end of the work.
This report should contain the following:
• information on the well (i.e., the well
construction report, type of well and a diagram
showing the well’s location on the property,
etc.);

91
• information on field procedures and personnel
involved in the test,
• information on the hydrogeologic setting,
including references to mapped aquifers.
• pumping test information including the date of
the pumping test, all data on the pump type,
depth of pump setting, pumping rates, method
of flow measurement, observations made during
the pumping test, duration of the test, available
drawdown, specific capacity, method of water

92
level measurements and water levels/times
recorded during the pumping test and recovery
period;
• analysis and assessment of the pumping test
data including an assessment of the long-term
sustainable yield and potential impacts to
neighbouring wells and/or streams.
Borehole Performance Curves
Borehole performance curves are best plotted
on a graph of water level against pumping rate.

93
Water levels are used (in metres below datum)
instead of drawdowns so that seasonal
variations can be plotted on the same graph if
the borehole is tested again at a different time of
year.
Multiple Production Wells:
For cases in which there are multiple production
wells, all such wells must be monitored during
the test.

94
In addition, the test must be conducted in a way
that will obtain information pertinent to the
operational needs of the entire well-field.
If wells may have to be operated simultaneously
in order to meet demand, the test must be
designed to produce data representative of these
conditions.

95
Limitations of pumping tests:
Analysing groundwater levels and pumping
rates measured during pumping tests provide
some indication of the behaviour or state of
‘health’ of the aquifer or groundwater system.
These tests undoubtedly provide valuable
information and help to understand the
groundwater system.

96
However, the decisions should be based on a
wider understanding of the regional geology,
hydrogeology and environment.
Conclusion:
The primary objective of the pumping test is to
obtain adequate information about aquifer as a
source of water supply and assess its capacity
for providing a safe yield of groundwater.

Procedure for conducting pumping tests

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