Environmental Engineering Reference
In-Depth Information
-
viii) The ratio of the contaminant input to the contaminant output
average risk
reduction rate (RRR) of the watershed. The RRR values calculated from measured
contaminant concentrations in the runoff from the diffusely contaminated area
were within the following ranges:
◦
=
As: 6.0-2.0-times
◦
Cd: 280-50-times
◦
Pb: 45-10-times
Zn: 90-20-times.
Following a pessimistic approach, the lowest RRR was used for calculating the
metal concentration of the runoff.
◦
-
ix) Calculation of the effect of the natural risk reduction, the removal of the
delineated sources and the remediation measures. The effect of the estimated min-
imum RRR on the metal content of the runoff is calculated dividing the input
concentration to the black box by the RRR:
◦
As: 296/2
=
148
µ
g/L
◦
Cd: 557/50
=
11
µ
g/L
◦
Pb: 1366/10
=
136
µ
g/L
g/L
Removal of the delineated mine waste dumps and isolation of the flotation tailings
dam will reduce the yearly metal emissions in the first year by a factor of 2.5
(estimated area-proportionally).
◦
◦
Zn: 72 772/20
=
3638
µ
As: 148/2.5
=
59
µ
g/L
◦
Cd: 11/2.5
=
4.4
µ
g/L
◦
Pb: 136/2.5
=
54.4
µ
g/L
g/L
5-10 times more reduction would be necessary, which cannot be reached by source
removal, given that the residual waste is highly dispersed on a large area or became
part of the soil. One remedial option is the chemical stabilization of contaminat-
ing metals. Immobilization/stabilization of metal ions by changing their chemical
forms to less mobile, less water-soluble, less bioavailable forms was achieved by
fly-ash and limestone addition. The combination of chemical stabilization with
phytostabilization in order to hinder dusting and erosion, the reduction of metal
emission is possible in an efficient way. Based on field experiments, combined
chemical and phytostabilization (CCP) will reduce dissolved-phase metal emis-
sions from diffuse sources as follows: As: 98%, Cd: 99.5%, Pb: 87%, Zn: 99.7%.
In addition, the estimated outflow from the watershed will be:
◦
◦
Zn: 3638/2.5
=
1455
µ
As: 59 * 0.98
=
1.2
µ
g/L
◦
Cd: 4.4 * 0.995
=
0.02
µ
g/L
◦
Pb: 54.4 * 0.87
=
7.1
µ
g/L
g/L
Combining the removal of some sources with stabilization of the residual con-
tamination all of the metals will reach the target (As: 10; Cd: 1; Pb: 10; Zn:
100
◦
Zn: 1455 * 0.997
=
4.4
µ
µ
g/L).
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