Experiment # 11
PUMPING TEST OF A TUBE WELL
Object: To investigate the pumping test of a tube well.
Apparatus: generator, power inverter and extension cords
submersible pump
discharge pipe, connections, reducers/enlargers
flow measurement device(s)
tape measure(s)
pressure transducer(s), cables, data logger(s)
electric water-level sounder(s) and batteries
steel tape(s) and carpenter’s chalk
watches/stopwatches
barometric sensor
thermometer
pH and conductivity meters
sample bottles
keys for wellhead locks and other infrastructure
toolkit, electrical tape, rope, wire ties, heat shrinks, duct tape, tarp, paper towels
lubricant/penetrating oil (e.g., WD-40)
flashlights/lanterns
data collection forms, logbook, permanent-ink pens
computer, calculator
graph paper (semilog, log) and/or computer software
references, standard operating procedures
manufacturer’s operating manuals for equipment
maps (site, geologic and topographic), cross section(s).
Theory: 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. 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.
A pumping test is a field experiment in which a well is pumped at a controlled rate and water-level response (drawdown) is measured in one or more surrounding observation wells and optionally in the pumped well (control well) itself; response data from pumping tests are used to estimate the hydraulic properties of aquifers, evaluate well performance and identify aquifer boundaries. 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.
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.
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 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.
e) To test the operation of the pumping and monitoring equipment,
f) To determine the effects of abstraction on neighboring 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? Are there likely to be any problems such as drawing in saline or polluted water after extended periods of pumping.
i) To help determine the correct depth at which the permanent pump should be installed in
the borehole
Important aquifer parameters are:
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.
Transmissivity: 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.
Storage coefficient, applicable for confined aquifers : volume of water released from
storage per unit surface area of a confined aquifer per unit decline in hydraulic head. It is
dimensionless.
Specific yield, applicable for unconfined aquifers : 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.
Specific yield is dimensionless or can be given in %.
Specific capacity of a well: ratio of discharge of the well to the drawdown, in m3/hour/m.
Observations:
Signature: __________
