In-situ immobilization of arsenic in the subsurface on an anthropogenic contaminated site - In-Situ Remediation of Arsenic-Contaminated Sites - page 143

Figure 7.2. Schematic cross-section through study area, concentrations show t-As as measured in 2005.

Table 7.1. Geochemical parameter characterizing the site before starting the pilot
trial (October 2008).

Depth Temperature pH EC Eh

[ ◦ C] [ µ Scm − 1 ] [m] [ − ] [mV]

StO-01 10 11.1 6.8 431 26

StO-02 21 10.0 5.0 207 65

StO-04 21 9.8 4.3 216 245

StO-06 10 10.4 6.1 227 88

StO-07 21 10.0 5.3 210 168

StO-08 21 10.7 5.8 301 19

StO-09 15 10.3 4.3 252 102

Well 1 10 7.9 196 142

Well 2 14 8.0 211 132

The site is characterized mainly by acid groundwater (pH 4.3-6.8) as measured in a field
campaign from October 20-22, 2008. However, the site characterization at the two locations of
the remediation well shows slightly alkaline groundwater ( Table 7.1 ). The electrical conductivity
(EC) ranges from 196 to 431 Scm − 1 . The redox conditions (Eh) is between 19 and 245 mV which

mean generally either iron & manganese reducing conditions or nitrogen reducing conditions.
This was verified by a campaign in 2006 where Fe(II)-concentration < 50

µ

gL − 1 were found
while Fe(III) was not detectable (Holländer et al ., 2008). Furthermore, the campaign in 2008
gave for sulfate (SO 4 ) 42mgL − 1 , for phosphate (PO 4 ) about 0 mg L − 1 , and for silica (SiO 2 )
3mgL − 1 .
Both remediation wells are bidirectional wells. For observation purposes, five observation
wells for sampling and monitoring of water parameters and levels have been installed ( Fig. 7.1 ) .

µ