Civil Engineering Reference
In-Depth Information
For the overall confined aquifer vulnerability assessment, the working maps
for relative concentrations for the first and second aquifers are overlaid, and the
product of the corresponding assessed relative concentrations is calculated for
each vertical characteristic profile corresponding to the mapping fragment:
(4.10)
cz t
(
*
, *)
=
c ztcz t
( *)(* )
,*
⋅
,*.
2
1
1
2
2
The obtained map for the resultant relative concentration
c
(
z
2
*
,
t*
) character-
izes the vulnerability of the second confined aquifer to the surface contamination.
In the same way as for the upper aquifer, the
predicted contamination poten-
tial
of the confined aquifer,
p = c
(
z
2
*
,
t*
)
∙w
, can be calculated and may serve as a
more refined flow-related characteristic of confined groundwater vulnerability.
For an assessment of the full groundwater vulnerability of the confined
aquifer, it is necessary to take the assessment depth
z
2
*
in the bulk of the aquifer,
for example, in its middle point by depth. On the modeling profile, in the course
of model implementation for the characteristic typical zones of the area, the
depth interval belonging to the aquifer bed is characterized by its corresponding
flow and transport parameters, especially by the higher hydraulic conductivity
k
2
(as compared to
k
0
of the overlying confining bed). In this case, when using
equation (4.7) for the calculation of the vertical flow velocity
w
, instead of
k
0
, the
average hydraulic conductivity value (between the confining bed and the aquifer
bed)
k
02
should be used and can be determined by equation (1.5) (see Chapter 1).
This note is also significant for the upper aquifer; that is, the average vertical flow
velocity
w
should be assessed taking into account the vertical hydraulic resistance
in the depth interval between the assessment depths of the first and second
aquifers,
z
1
*
and
z
2
*
(Figure 4.1).
The described methodology of groundwater vulnerability and protectability
assessment for the second (confined) aquifer from the surface can also be applied for
even deeper aquifers (third or fourth from the surface and deeper). In this case, in the
same way as for the second aquifer, at the preparatory stage of analysis of the ground-
water heads (levels), the zones of downward (mostly within watersheds) and upward
(in the river valleys) flow are found as shown in Figure 4.1 [
Shestopalov
, 1988].
Starting from the upper aquifer, assessment is performed for the zones of
downward flow successively for each aquifer at control depths
z
1
*
,
z
2
*
,
z
n
*
according
to the procedure described above.
As a result, in the same way as in equation (4.9) for two aquifers, for the
aquifer system of
n
aquifers we obtain the area distribution of the cover or full
groundwater protectability
ε
depending on the assessment depth
z
n
*
determined
by the sum of
n
partial indexes for the successive aquifers of the system:
n
∑
ε=−
log( *)
cz t
*
,
=−
log
c zt
( *)
,
* ,
(4.11)
n
i
i
i
=
1
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