Civil Engineering Reference
In-Depth Information
10
−5
to 10
−3
m/day and characteristic
m
0
values of 5, 10, 20, 30, 40, and 50 m, Goldberg
obtained the range of α =
m
0
/
k
0
to be approximately 10
3
- 10
7
days, and determined
six categories for the confined groundwater protectability assessment as follows:
Category I:
m
0
≤ 5 m, or α ≤ 10
3
Category II: 5 m <
m
0
≤ 10 m, or 10
3
< α ≤ 10
4
Category III: 10 m <
m
0
≤ 20 m, or 10
4
< α ≤ 10
5
Category IV: 20 m <
m
0
≤ 30 m, or 10
5
< α ≤ 10
6
Category V: 30 m <
m
0
≤ 50 m, or 10
6
< α ≤ 10
7
Category VI:
m
0
> 50 m, or α > 10
7
The higher the category, the higher the groundwater protectability.
In addition, Goldberg determined three basic groups of confined groundwater
protectability based on the confining bed thickness
m
0
and ratio of groundwater
heads (levels) in the upper (unconfined) aquifer,
H
1,
and in the assessed confined
aquifer,
H
2
:
I.
Protected
. The groundwater is confined by a continuous (in area) perme-
ability formation with thickness
m
0
> 10 m and
H
2
>
H
1
.
II.
Conditionally Protected
. The groundwater is confined by a continuous
(in area) low-permeability formation with thickness 5 m ≤
m
0
< 10 m and
H
2
>
H
1
(case
a
) or thickness
m
0
> 10 m and
H
2
≤ H
1
(case
b
).
III.
Unprotected
. The groundwater is confined by a thin confining
formation with
m
0
< 5 m and
H
2
≤
H
1
(case
a
) or when the confining
formation is discontinuities (presence of lithological “windows,” zones of
intensive fracturing, faults) at any ratio between
H
2
and
H
1
(case
b
).
Confined groundwater should also be considered as
unprotected
in the
following cases: in the river valleys when the confining layer is cut through by the
river in the karst areas when the confining layer is subjected to karst processes, and
under the unfavorable tectonic conditions (presence of intensive neotectonic move-
ments in the active water exchange zone, high conductivities in faults).
In group I the groundwater protectability is guaranteed by the high thickness
of the confining layer and by hydrodynamic conditions at which the downward
groundwater flow from the unconfined aquifer is impossible.
A quantitative
upper groundwater protectability assessment
by Goldberg is
performed directly by the calculation of percolation time
t
w
using formula
(1.1), (1.2), or (1.3). Setting the base at the
maximum contaminant lifetime
,
which is assessed to be 400 days for most of bacteria, and some kinds of pesticide
contamination, Goldberg determined six groundwater protectability categories,
as given in Table 1.3.
For the
confined groundwater
, the time of groundwater percolation through
the confining bed (at downward flow direction,
H
1
>
H
2
) is calculated as
2
mn
kH
t
w
=
0
,
(1.6)
0
∆
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