Geology Reference
In-Depth Information
Figure 11 shows Mise-à-la-masse and SP equipotential map near borehole
no. 265. This bore-well drilled up to 42 m struck water at a depth of 23 m
in pink granite and has static water level at 21.18 m. The drill log of existing
bore-well indicates minor fractures between 15.84 and 32.90 m and fractured
pink granite from 32.90 to 37.50 m. Well developed fractures with high
density from 32.90 to 37.50 m substantially increased the yield of the well
to 100 lpm. The current electrode in the bore-well was lowered down to
depth of 37 m. Mise-à-la-masse map shows a well-developed trend of high
equipotential zone in N-S direction along the central profile across the
borehole. This indicates the extension of the fractures in N-S direction. SP
map also shows similar trend in N-S direction. Two bore-wells (BW-1 and
BW-2), one each on southern and northern side of the existing bore-well
recommended on the basis of the Mise-à-la-masse measurements intercepted
fractures at nearly the same depth as in borehole no. 265. A bore-well (BW-
3) recommended on hydrogeological consideration in NW of existing bore-
well did not intercept any fracture. This confirms the extension of fracture
in N-S direction only.
DISTANCE IN METRES
Contour Interval = 2 mv
Station Interval = 4 m
Measurement Traverses
with observation stations
Figure 11.
Mise-à-la-masse (above) and SP equipotential
map (below) at IFP-11.
CONCLUSION
Many geophysical techniques have been applied to groundwater investigations
with some giving more success than others. For resource mapping, it is not
the groundwater itself that is the target of the geophysics rather it is the
geological situation in which the water exists. Potential field methods, gravity
