Civil Engineering Reference
In-Depth Information
Table 1.3
Categories of Goldberg's quantitative upper groundwater protectability
assessment.
Groundwater
protectability
category
I
II
III
IV
V
VI
Percolation time
t
w
, days
t
w
≤ 10
10
< t
w
≤ 50
50
< t
w
≤ 100
100
< t
w
≤ 200
200
< t
w
≤ 400
t
w
> 400
Table 1.4
Groups and gradations of confined groundwater protectability by
percolation time
t
w
through low-permeable confining bed.
Groundwater
protectability group
Unprotected
Conventionally protected
Gradations
1
2
3
4
5
t
w
, years
t
w
< 1
1 <
t
w
≤ 5
5 <
t
w
≤ 10
10 <
t
w
≤ 20
t
w
> 20
where
n
is the porosity of the confining bed (usually taken to be 0.01).
Corresponding confined groundwater protectability gradations and groups are
given in Table 1.4.
Comparing the assessed
t
w
value with known lifetimes for definite contam-
inants, a special groundwater protectability assessment can be done for these
contaminants.
The groundwater protectability assessment system described above and
developed by Goldberg was the first theoretically grounded solution of the given
problem. The system has been used with different modifications and generaliza-
tions in Russia until recent times [
Goman
, 2005;
Michnevich
, 2011].
It should be noted, however, that a groundwater protectability assessment
based on the time of water percolation through the overlying deposits determined
for different cases by formulas (1.2)-(1.4) and (1.6) is in most cases not complete
enough because it assesses only
cover
groundwater protectability and does not
account for the protective capacity of the aquifer itself.
In the case of infiltration of contaminated water from the surface,
calculations of the water percolation time
t
w
through the unsaturated zone by
formula (1.3) show that the assessed percolation time appears to be small enough.
For example, at infiltration rate
w
c
= 100 mm/year and a 10 m thick unsaturated
zone with effective porosity 0.01 composed of heavy loams and clays with
hydraulic conductivity 0.001 m/day, formula (1.3) gives a
t
w
equal to only 239
days. This result is in agreement with the conclusion by
Haustov
[2007] that the
cover protectability of upper groundwater, even in a thick unsaturated zone
(over 10 m) composed of low-permeability deposits (loams, clays) is always
insufficient for groundwater protection from contaminants. For this reason, the
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