Significant results in the range from 30 to 60% were obtained on June 2 for
DCC2.2 and DCC2.3 and on June 22 for DCC2.3, evidencing that the abatements
were ascribed to the injection of nZVI solutions. The progressive decrease in the
abatements, as illustrated/highlighted for DCC2.2, is in agreement with the relative
loss in reactivity of iron particles.
Evolution of Alkalinity Expressed as Bicarbonate and of Chloride Content
Table 6.20 presents alkalinity expressed as bicarbonate concentration and chloride
concentration in the sampled water at two levels (H and B) of each control piezometer of line 2.
In comparison to 2014, Cl
À content and alkalinity expressed by bicarbonate
concentration remained in the same order of magnitude whatever the PZ, the
depth, and the sampling date. These results evidence that the injection of nZVI
particles did not affect the natural attenuation that was occurring.
Evolution of TCE, cis-1,2-DCE, 1,1-DCE, and VC Content
Table 6.21 presents the individual evolution of TCE, cis-1,2-DCE, 1,1-DCE, and
VC concentration in cPZs of line 2. The reduction of the tCOCs in DCC2.1 and
DCC2.2 relates to TCE, cis-1,2-DCE, and 1,1-DCE, with a relative increase in VC
content. This shows the limitation of the treatment due to an insufficient nZVI load
on DCC2.2 and DCC2.3 levels.
In DCC2.1, whatever the sample date or depth, COCs content remained globally
in the same order of magnitude from August 2014 to July 2015. However, data
presents some characteristics that have to be discussed. From June 2 to July 8, TCE
content decreased in the range from 15 to 27%. In the same time, VC content
remained in the same order of magnitude, whereas cis-1,2-DCE and 1,1-DCE
content increased up to 25% and 14%, respectively. Between June 2 and June
22, the slight decrease in TCE content was accompanied by a slight enhancement
of cis-1,2-DCE content. In the same time, a slight decrease in 1,1-DCE content is
accompanied by a slight increase in VC. Between June 22 and July 8, the decrease in
TCE and cis-1,2-DCE content was accompanied by the increase in 1,1-DCE content,
while VC content slightly decreased. These results tend to evidence the occurrence
of biological processes in agreement with the natural attenuation (Morrison and
Murphy 2006). As already discussed, the slight decrease in VC content between
June 22 and July 8 could result from a temporary bio-oxidative process due to the
sampling and the measurements campaign. The pursuit of TCE biodechlorination
strengthened that anaerobic reactions continued after the consumption of oxygen.
Regarding DCC2.2, only the data acquired in June 2 showed a practical interest.
In comparison with 2014, results clearly evidenced treatment effect of nZVI. The
drastic decrease observed for TCE, cis-1,2-DCE, and 1,1-DCE content, respectively
up to 94%, 31%, and 66%, resulted in the increase in VC content up to 90%.
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R. Rodrigues et al.
DCC2.2 and DCC2.3 and on June 22 for DCC2.3, evidencing that the abatements
were ascribed to the injection of nZVI solutions. The progressive decrease in the
abatements, as illustrated/highlighted for DCC2.2, is in agreement with the relative
loss in reactivity of iron particles.
Evolution of Alkalinity Expressed as Bicarbonate and of Chloride Content
Table 6.20 presents alkalinity expressed as bicarbonate concentration and chloride
concentration in the sampled water at two levels (H and B) of each control piezometer of line 2.
In comparison to 2014, Cl
À content and alkalinity expressed by bicarbonate
concentration remained in the same order of magnitude whatever the PZ, the
depth, and the sampling date. These results evidence that the injection of nZVI
particles did not affect the natural attenuation that was occurring.
Evolution of TCE, cis-1,2-DCE, 1,1-DCE, and VC Content
Table 6.21 presents the individual evolution of TCE, cis-1,2-DCE, 1,1-DCE, and
VC concentration in cPZs of line 2. The reduction of the tCOCs in DCC2.1 and
DCC2.2 relates to TCE, cis-1,2-DCE, and 1,1-DCE, with a relative increase in VC
content. This shows the limitation of the treatment due to an insufficient nZVI load
on DCC2.2 and DCC2.3 levels.
In DCC2.1, whatever the sample date or depth, COCs content remained globally
in the same order of magnitude from August 2014 to July 2015. However, data
presents some characteristics that have to be discussed. From June 2 to July 8, TCE
content decreased in the range from 15 to 27%. In the same time, VC content
remained in the same order of magnitude, whereas cis-1,2-DCE and 1,1-DCE
content increased up to 25% and 14%, respectively. Between June 2 and June
22, the slight decrease in TCE content was accompanied by a slight enhancement
of cis-1,2-DCE content. In the same time, a slight decrease in 1,1-DCE content is
accompanied by a slight increase in VC. Between June 22 and July 8, the decrease in
TCE and cis-1,2-DCE content was accompanied by the increase in 1,1-DCE content,
while VC content slightly decreased. These results tend to evidence the occurrence
of biological processes in agreement with the natural attenuation (Morrison and
Murphy 2006). As already discussed, the slight decrease in VC content between
June 22 and July 8 could result from a temporary bio-oxidative process due to the
sampling and the measurements campaign. The pursuit of TCE biodechlorination
strengthened that anaerobic reactions continued after the consumption of oxygen.
Regarding DCC2.2, only the data acquired in June 2 showed a practical interest.
In comparison with 2014, results clearly evidenced treatment effect of nZVI. The
drastic decrease observed for TCE, cis-1,2-DCE, and 1,1-DCE content, respectively
up to 94%, 31%, and 66%, resulted in the increase in VC content up to 90%.
362
R. Rodrigues et al.