Groundwater lies almost everywhere below the earth's surface.
In Canada, an average 25% of the water supply comes from groundwater.
In addition, groundwater is one of our most important sources
of water for irrigation.
Understanding The Basics of Water Wells
A well is an access, a port to the water present in the
subsurface. It is in most cases either cased to be in contact
with the saturated soil or drilled to intercept fractures
where water flows.
Water is present in the subsurface in the void between soil
particles (pores) or in rock fractures or interstices that
result from the formation or history of the rocks (e.g. earthquakes)
or due to dissolution (for specific rock formations). When
all the pores or fractures are filled with water (or saturated),
the combination of the soil or rock formation and the water
is called an aquifer.
When pumping a well, the water in the well is lowered. The
drop in elevation in the well is called a drawdown. Due to
the drawdown, a difference between the water level at a distance
from the well which is higher (or presents a higher level
of energy) and the water level in the well (lower and at a
lower level of energy) is created. This translates in a flux
of water from the highest to the lowest level of energy that
results in a flow of water towards the well.
The flow of water towards a well can be compared to the flux
of energy from a building to the outside. The drawing illustrates
a building where a temperature is maintained at a higher level
than the outside temperature. This creates a flow of energy
from the building to the outside, through the walls. To maintain
the temperature in the building, a source of energy is required,
and it is the input of energy that creates the temperature
rise in the building that triggers the flux of calories from
the building to the outside.
In the case of a water well, the energy is provided to extract
water from the well. This energy input indirectly creates
a drawdown (or drop of water level) in the well. The resulting
difference between the water level in the well and in the
aquifer is similar to the difference of temperature between
the inside and outside of the building. A flux of water will
be created between the aquifer and the well. By keeping pumping,
the drawdown will be maintained, thus keeping the movement
of water towards the well.
The volume of water extracted from a well comes from a volume
of aquifer in the subsurface. The area where infiltration
due to precipitation or recharge associated with movement
of groundwater contributes to this volume of aquifer is called
the capture zone. From the well outward, the time taken by
the groundwater within the capture zone to reach the well
can be tracked in time and is referred to as travel time.
to download a PowerPoint presentation on Well Development.
(Please Note: This is a large file and downloading may take
some time depending on your Internet connection speed)
The following links may be in PDF format. If required, you
can download Adobe Reader here.
Canada: Water Efficiency
and Human Health
What Private Well Owners Should Know
Conservation Foundation presses for better local water
The Japanese group People
for Rainwater Utilization