Civil Engineering Reference
In-Depth Information
positive. Such sites require special attention with respect to the corresponding
vertical flow velocity
w
assessment because in cases of
m
0
being close to zero,
equation (4.7) may lead to high inaccuracy. However, in the real situation of
a “hydrogeological window,” instead of low-permeable deposits of the
confining bed as in the background undisturbed area, there are higher-
permeable deposits (for example, sands or loamy sands instead of loams) in
such a window. For this reason, equation (4.7) can still be formally used (under
higher attention), and there is no need to set
m
0
to zero, but it is more correct
to increase (usually 5-10 times or even more) the vertical conductivity
k
0
.
If deep PFMZs related to the discontinuity of the confining bed widely occur
and occupy a significant part of the total study area, they require a separate
typical model to be implemented and a corresponding vertical predicted
concentration profile
c
2
(
z
,
t*
) obtained for these zones.
4.
Next, the obtained maps for zones of the confining bed thickness (map 1)
and vertical flow velocity (map 2) are overlaid and the resultant zoning map
is obtained. Each zone on this map corresponds to definite average values of
the confining bed thickness
m
0
and vertical flow velocity
w
.
5.
For each obtained zone with definite average values of
m
0
and
w
, the absolute
depth mark
z
2
*
is found on the vertical axis Z, corresponding to the assessment
depth of the confined aquifer. If the assessment depth
z
2
*
corresponds to the
upper boundary of the confined aquifer (just below the confining bed), then
the assessment gives the
cover
vulnerability or protectability of the confined
aquifer. For the assessment of full groundwater vulnerability or protectability,
it is necessary to relate
z
2
*
with a depth of the real groundwater intake (within
the aquifer body). Then the corresponding local model coordinate
z
=
z
2
*
−
z
1
*
is found, and by the intersection of this depth level with the corresponding
plot of predicted relative concentration
c
2
(
z
,
t*
) for the given vertical flow
velocity
w,
the relative concentration at the absolute depth of the assessed
confined aquifer,
c
2
(
z
2
*,
t*
), is determined. This relative concentration
characterizes the additional vulnerability of the confined aquifer determined
by the state of the permeability of the overlying confining bed. The area
distribution is then calculated for the additional groundwater protectability
index ε
2
= - log
c
2
(
z
2
*
,
t*
) on account of the attenuation capacity of the
confining bed. The working map for this index is then built.
6.
The final assessment is performed of the cover or full groundwater
protectability of the second confined aquifer, from the surface accounting for
the previously assessed protectability of the upper aquifer (see Section 4.1),
by overlaying the working maps and summing the corresponding indexes
ε
1
and
ε
2
of the first and second aquifers for the corresponding characteristic
vertical profiles:
c zt
(4.9)
εεε
=+=
1
-log
cz t
(* )
,*-log
( *)
,*.
2
11
22
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