Environmental Engineering Reference
In-Depth Information
Table 3
Arsenic concentration in groundwater related to sampling occasion, groundwater table
level, K
d
value, Fe concentration and sample treatment
Sampling
occasion Gwt (m) K
d
value
a
As conc (µg/L) Fe conc (µg/L) Sample treatment
Nov 21, 2007 0.9 410 610 23 Filtered on site and
in laboratory
Nov 21, 2007 0.9 190 1,300 23 Unfiltered, acidified
in laboratory
Nov 27, 2007 0.9 90 2,800 24000 Analysis redone
March 3, 2008,
acidified in
laboratory
Dec 17, 2007 0.8 6 42,000 110 Filtered on site
Feb 07, 2008— 0.7 20 12,300 − Filtered on site,
acidified in
laboratory
Feb 07, 2008 0.7 200 1,260 − Filtered on site and
in laboratory
a
Calculated using a mean As concentration in the soil of 250 mg/kg DS. Concentration was
calculated as a mean of all the analyzed soil samples from sampling points in the area.
to sample treatment and sampling occasion. Results also indicate that a fast
complex formation occurs even after filtration of the sample.
The total As concentration is also dependent on the level of the groundwater
table. Groundwater samples collected when the table was high contained more
As compared to those collected when the table was lower (42 mg/L at 0.7 m and
0.61 mg/L at 0.9 m). This is probably due to the fact that, as it elevates, the ground-
water reducing environment dissolves As that is bound to iron hydr/oxides in soil
particles
[12]
. As the groundwater table fluctuates, As in soil can be dissolved into
the groundwater, thus increasing the As concentration. Arsenic concentrations vary
locally due to changes in the groundwater table level, inflow and precipitation
[12]
.
At the site, the highly polluted area is mostly covered with asphalt, and stormwater
is conducted through pipes to the stream. Direct infiltration of surface water is
therefore small. It is considered that the seawater level has a large impact on the
groundwater table level. As the groundwater is in direct contact with the seawater,
a rise in the seawater level makes the As in the soil dissolve into the groundwater.
The calculated Kd values are significantly lower in the groundwater samples
compared to those obtained in batch and leaching tests (Tables
1
-
3
). Kd values are
more than 300 times higher in the leaching tests and up to 7,500 times higher in
the batch tests compared to the groundwater samples. This is because the rate of
As dissolution from iron arsenate is higher in groundwater since it is a more
reducing environment
[13]
. In addition, the higher salinity of groundwater probably
causes more As to dissolve, since particulate Fe concentrations decrease with
increasing salinity
[14]
.
EU directive 2003/33/EG states that excavated material should be classified
according to batch test results
[20]
. The present study demonstrate that the
