Characterizing Aquifers - Hydrogeology: Objectives, Methods, Applications - page 132

Calculating the permeability, K, follows from the monitoring of the
volume injected or withdrawn, and the resulting variations in level. It
also takes into account the geometric characteristics of the slice under
consideration (height and diameter).
5.2.2 Lugeon tests
The Lugeon method is used in more or less fractured areas of massive
rock (limestone, sandstone, granite), and consists of injecting water under
pressure into 2 to 5 m long slices of terrain, isolated from the overlying
sections by a valve.
One measures the injected discharge over a given period of time (5 or
10 minutes), while increasing the pressure in a stepwise manner (from 1 to
10 bars), then decreasing it in the same way. The volume of injected water
is calculated, and is then used to deduce the terrain's absorption in liters
per minute and by linear meters of depth at the different pressure levels.
The lugeon is a unit describing this value at a pressure of 10 bars, and it is
generally accepted that one lugeon corresponds to a permeability on the
order of 1.5⋅10 -7 m·s -1 .
This method allows for interesting vertical and lateral comparisons in
a rock unit. It is frequently used in the context of dam and tunnel studies,
and allows for a good approach to injection possibilities.
5.2.3 Micro-turbine fl ow meter measurements
These measurements, taken in a tubed and perforated borehole, with the
help of a small-diameter turbine, allow the detection of vertical water
circulation, whether ascending or descending.
It does not truly measure the permeability of the environment, but it
determines the positions of the most productive horizons and the current
speed, which allows for the calculation of circulation discharges. This
method is highly used in determining water drilling diagnostics.
5.3 Pumping tests
Unlike periodic tests, which describe only very limited permeable horizons,
pumping tests examine the entire thickness of the aquifer (in complete
wells), or a suffi ciently representative section (incomplete wells). They
provide variable information, depending on the conditions of the test and
the nature of the equipment: