Geology Reference
In-Depth Information
8
Analyses of Aquifer Parameters
from Different Hydraulic Tests
and Their Scale Effect
J.C. Maréchal, Faisal K. Zaidi
1
and B. Dewandel
Hard Rock Aquifer Unit, BRGM, Montpellier, France
1
National Geophysical Research Institute, Hyderabad, India
INTRODUCTION
Slug test is based on the principle of the analysis of the rate of water level
fluctuation in a well after a certain volume of water (slug) has been suddenly
added or removed from the well. However one limitation of conducting slug
tests in this manner is that if the tests are being conducted for environmental
monitoring purposes it is not advisable to inject or take out a certain volume
of water in the well as it may disturb the ambient water quality or it may
produce hazardous wastes. To overcome this problem, it is common to insert
an iron cylinder of a known volume in the well. The length of the cylinder
may vary from 1 to 1.5 metres with a cord tied to one end which facilitates
the cylinder to be lowered quickly below the water level and later to be
quickly raised above the water level. This instantaneous lowering and raising
of the slug in the bore-well causes a cone of depression or suppression
which can be related to a pumping or injection tests. The corresponding
changes in water levels are recorded in the bore-well with the help of a water
level recorder. With this record of the rate of recovery or recession of the
water level, the transmissivity or the hydraulic conductivity of the borehole
can be measured (Kruseman and de Ridder, 1994). Generally slug tests can
yield good results of hydraulic conductivity for formations which have low
permeability. For highly permeable formations, such as alluvial aquifers,
slug tests cannot be very successful as the disturbance in water level created
by the slug dissipates very fast in the formation and it is difficult to measure
the corresponding water level changes. Of course the development of
automatic water level recorders with the capability of taking regular
