In-situ immobilization of arsenic in the subsurface on an anthropogenic contaminated site - In-Situ Remediation of Arsenic-Contaminated Sites - page 142

Figure 7.1. Top view of study area.

the org-As-compounds due to their complexity directly. The inorganic As-fraction (i-As: As(III)
and As(V)) ranges between 6% and 87% with a mean value of 37% and a median value of 32%.
At the investigated site, during both world wars CWA were investigated, produced and tested.
Additionally, CWA were disposed of using incineration and burying between and after the wars.
Finally, the CWA reached soils and groundwater by this improper handling. The site as well as
the sampling and measurement technique have been described in detail by Holländer et al . (2008)
and Krüger et al . (2008). The remediation of the site is ongoing with a pump-and-treat facility
having a capacity of 190 m 3 h − 1 . In the facility org-As is being removed by activated carbon.
In the beginning of the remediation process i-As was removed by granulated ferric hydroxides
(Driehaus, 2002; Driehaus et al ., 1998). Later, the granulated ferric hydroxide in the filters has
been replaced by activated carbon as well.
We installed a pilot plant for the in-situ immobilization of arsenical CWA on the site. Since
several hot-spots can be found, the pilot plant was installed downstream of one hot-spot. The
source of the hot-spot was a former CWA storage bunker ( Fig. 7.1 ). After WW II, the arsenic
containing CWA from the bunkers cisterns were burned next to the bunker in open zinc tanks by
adding kerosene. Huge amounts of CWA and their degradation products infiltrated into the soil
and further into the groundwater due to tank corrosion and accumulation of arsenic in combustion
residues.
A schematic cross-section of the site and the study area is shown in Figure 7.2 . The sandy
aquifer with a hydraulic conductivity of about 4.5 10 − 4 ms − 1 determined by pumping tests and

a thickness of 40 m is roughly divided into two layers by marl lenses which act as local aquitards.
The groundwater flow direction is from NE to SW.
The depth to the groundwater table is 5 to 7 m. The vertical markers indicate monitoring wells
as well as two remediation wells (Well 1 and Well 2) which were built for the pilot plant. The t-As
concentrations as measured in 2005 are given next to the well screens (dashed lines). Thus, the
As plume is apparently sinking below a marl lens (aquitard) in the southern direction ( Fig. 7.2 ).

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