Environmental Engineering Reference
In-Depth Information
-
Tier 2
Transport modeling taking partition and biodegradation also into consideration
and comparing the resulting PEC value to generic WQC.
-
Tier 3
Comparing calculated PEC to the river-specific aquatic no effect concentration
(based on biological indicators).
-
Tier 4
Evaluation of uncertainties.
According to this concept one can stop with further refined assessment when the
result of the previous tier of the risk assessment is negative.
Results of the risk assessment of case study 2
-
Tier 1 and Tier 2.
Measured contaminant concentrations in the groundwater from wells No. 1, 3 and
7 and the relevant groundwater quality criteria (GWQC) are shown in Table 10.2.
-
Modeling:
Solution
of
the
governing
equation
including
advection,
dispersion
and
retardation:
exp
x
2
1
1
/
2
1
C
(
x
,0,0,
∞
)
4
λα
x
DF
p
=
=
−
+
C
(0, 0, 0, 0)
α
v
c
x
erf
erf
z
x
)
1
/
2
[2]
S
w
4
α
y
x
1
/
2
S
d
×
4
(
α
where
-
x
=
distance between the source and the creek (15 m);
-
S
w
,
S
d
=
width and height of the plume in the source;
-
α
x
,
α
y
,
α
=
dispersivity in x, y, z directions
z
-
DF
p
=
dilution factor along the plume;
-
λ =
biodegradation rate or half-life time;
-
V
c
=
transport velocity of the contaminant;
-
erf
=
error function.
Table 10.2
Measured concentrations in the groundwater and the applied groundwater quality criteria.
Intervention
Intervention
Sampling
Sampling
Sampling
HU
value GW
value GW
Contaminant
point 1
point 7
point 3
GWQC
HU (2000)
NL (2000)
TPH (
µ
g/L)
8350
4757
0
100
2000
600
Benzene (
µ
g/L)
7330
6590
99
1
20
30
Toluene (
µ
g/L)
11 000
7720
10
20
80
130
Ethylbenzene (
µ
g/L)
1110
1570
0
20
80
150
Xylene (
µ
g/L)
8300
6420
0
20
80
70
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