Environmental Engineering Reference
In-Depth Information
Fig. 3
A comparison of filtered and non-filtered samples in terms of As speciation of groundwater
from the well in the highly contaminated area
leachability of As is underestimated in batch tests. Thus, excavated material can be
classified as less hazardous than it is in reality.
On site filtration is crucial for the result of As speciation in water. If the water
sample is not filtrated on site, iron oxides and soil particles containing oxides will
remain. Arsenic(V) then reacts with these iron oxides and precipitates, while As(III)
does not because it is not as easily adsorbed to metal oxides
[12]
. If the Fe content
of the water sample is high, this effect can be significant. Thus, by not filtrating on
site, the result for As(V) can be misleading. Figure
3
shows the As speciation in
groundwater when the sample was filtrated compared to when it was not filtrated on
site. DMA and MMA concentrations were low in all samples (0.050-0.55 mg/L).
This was expected, because the organic content of the soils is low
[12]
.
Conclusions
The investigated site is highly contaminated by As in both soil and groundwater
and remedial actions are urgently needed. The groundwater concentrations of
As(III) were high, despite the low amounts leached in the laboratory tests. Batch
tests under aerobic conditions are not an appropriate method for determining the
leachability of As from soil, because there is a risk that excavated material will be
classified as less hazardous than it is in reality. Filtration of groundwater samples
in the field is necessary. If the sample is not filtrated immediately, iron hydr/oxides
