Civil Engineering Reference
In-Depth Information
properties of rocks; and interrelation of groundwater heads (levels) in the
studied and overlying aquifers.
2.
Technogenic
Factors Presence of contaminants on the land surface (waste
collectors, slurry tanks, pits, outflow of wastewater over the watershed
areas, irrigation with wastewater, etc.) and character of contaminant influx
to groundwater determined by these conditions.
3.
Physicochemical
Specific properties of contaminants, their migration, sorp-
tion, and degradation properties chemical stability, and interaction with
groundwater and rocks.
According to
Goldberg
[1983], the complete groundwater protectability
assessment requires all the above factors to be taken into account. As a complex
characteristic determining the risk of groundwater contaminatnion, Goldberg
introduces the groundwater
susceptibility П
to contamination as determined by
the ratio
Π
=
M
/,
ε
(1.1)
T
where
M
T
is the module of the technogenic load assessed in thousands of tons
of contaminant fallout per square kilometer of land surface in a year, and
ε
is
the dimensionless
groundwater protectability index
assessed in relative units.
From the above three main groundwater protectability factors, the natural
ones are of primary importance because they determine the degree of the natural
protection of an aquifer from any contaminants and conditions of their penetra-
tion from the land surface. Among the natural factors, the most important is the
presence of overlying low-permeable deposits: clays, heavy loams, loams, sandy
loams, and loamy sands with hydraulic conductivity
k
below 0.1 m/day.
Quantitatively the groundwater protectability can be characterized by the
dimensionless index
ε
as described below.
As the main parameter of groundwater protectability, Goldberg used the
percolation time t
w
that is the time needed for percolating contaminated water
from the land surface to reach the groundwater table. For the upper (unconfined)
aquifer the time
t
w
is assessed for the following two scenarios:
1.
Flow of contaminated (waste) waters from the surface basins with constant
level
H
c
. The percolation time is determined by the formula
(
)
(
)
−+
(
)
t nnHkmH
=−
/
/
ln
1/
m H
,
(1.2)
w
e
c
c
c
where
H
c
is the height of the wastewater column in the basin (the average
value
H
c
=
5 m is usually taken in groundwater protectability assessments),
k
the unsaturated zone hydraulic conductivity (m/day),
m
the unsaturated zone
thickness (m),
n
the porosity, and
n
e
the initial soil moisture content in the
unsaturated zone.
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