295
Permeable Reactive Barriers in Europe
Connelly, Chicago, USA) is used for cVOCs (mainly TCA, TCE, and PCE) degradation. Monitoring results over 4 years of operation indicated an effective
removal of cVOCs at 92.4%–97.5%. However, the continuous loss of porosity
due to mineral precipitation was identified as a significant problem, given the
high concentrations of calcium, which may significantly decrease the hydraulic performance of the PRB and may consequently limit its longevity to about
10 years only (Lo et al., 2003, Lai et al., 2006). A detailed monitoring campaign
over 7.5 years after the barrier’s erection showed very efficient removal (>99%)
for the most important cVOCs (PCE, TCE, and 1,1,1-TCA). However, significant formation of cis-DCE within the PRB resulted in an overall insufficient
removal of cis-DCE (≈ 80%). High concentrations of both TCE and cis-DCE
upstream the PRB along with the significant formation of cis-DCE inside the
PRB which gave rise to significant concentrations of cis-DCE downstream the
PRB. This finding was not acceptable from a regulatory perspective and further remedial action was needed to remove the cis-DCE plume discharging
into a small creek located about 100 m downstream the PRB. Another PRB
located on the downstream side of the existing PRB (only treating the very
narrow cis-DCE plume) was a possible solution. On the basis of the concentrations observed on the downstream side of the PRB, a relatively thick barrier
was needed to meet target criteria of 10 μg/L. Enhanced NA by augmenting
with cis-DCE degrading bacteria (Dehalococcoides species) in the downstream
aquifer was another option (Muchitch et al., 2011).
13.4.2 Copenhagen Freight Yard
Set up in 1998; type: continuous trench (CRB), length: 15.2 m, depth: 6 m,
thickness: 0.9 m, and full-scale, ZVI for treating cVOCs (up to 4 mg/L,
mainly cis-DCE). Effective treatment of the upgradient concentration, however, a part of the plume that migrated around the barrier, hydraulic conductivity decreased significantly during an operational term of 18 months,
probably due to gas evolution (Kiilerich et al., 2000; Vidic, 2001; Henderson
and Demond, 2011).
13.5 First PRB Site in Italy
13.5.1 Avigliana, Near the City of Torino (Piemonte Region)
Set up in 2004; type: CRB, 120 m long, 13 m deep, and 0.6 m thick; full-scale;
ZVI for cVOCs (up to 300 μg/L, mainly TCE, cis-DCE). Effective treatment
of upgradient contamination within the first 3 years, but tests conducted
within the PRB found a decrease of hydraulic conductivity by two orders
of magnitude, due to the biopolymer (i.e., guar gum) applied during excavation of the barrier. This stimulated the microbial activity of sulfate reducers
Permeable Reactive Barriers in Europe
Connelly, Chicago, USA) is used for cVOCs (mainly TCA, TCE, and PCE) degradation. Monitoring results over 4 years of operation indicated an effective
removal of cVOCs at 92.4%–97.5%. However, the continuous loss of porosity
due to mineral precipitation was identified as a significant problem, given the
high concentrations of calcium, which may significantly decrease the hydraulic performance of the PRB and may consequently limit its longevity to about
10 years only (Lo et al., 2003, Lai et al., 2006). A detailed monitoring campaign
over 7.5 years after the barrier’s erection showed very efficient removal (>99%)
for the most important cVOCs (PCE, TCE, and 1,1,1-TCA). However, significant formation of cis-DCE within the PRB resulted in an overall insufficient
removal of cis-DCE (≈ 80%). High concentrations of both TCE and cis-DCE
upstream the PRB along with the significant formation of cis-DCE inside the
PRB which gave rise to significant concentrations of cis-DCE downstream the
PRB. This finding was not acceptable from a regulatory perspective and further remedial action was needed to remove the cis-DCE plume discharging
into a small creek located about 100 m downstream the PRB. Another PRB
located on the downstream side of the existing PRB (only treating the very
narrow cis-DCE plume) was a possible solution. On the basis of the concentrations observed on the downstream side of the PRB, a relatively thick barrier
was needed to meet target criteria of 10 μg/L. Enhanced NA by augmenting
with cis-DCE degrading bacteria (Dehalococcoides species) in the downstream
aquifer was another option (Muchitch et al., 2011).
13.4.2 Copenhagen Freight Yard
Set up in 1998; type: continuous trench (CRB), length: 15.2 m, depth: 6 m,
thickness: 0.9 m, and full-scale, ZVI for treating cVOCs (up to 4 mg/L,
mainly cis-DCE). Effective treatment of the upgradient concentration, however, a part of the plume that migrated around the barrier, hydraulic conductivity decreased significantly during an operational term of 18 months,
probably due to gas evolution (Kiilerich et al., 2000; Vidic, 2001; Henderson
and Demond, 2011).
13.5 First PRB Site in Italy
13.5.1 Avigliana, Near the City of Torino (Piemonte Region)
Set up in 2004; type: CRB, 120 m long, 13 m deep, and 0.6 m thick; full-scale;
ZVI for cVOCs (up to 300 μg/L, mainly TCE, cis-DCE). Effective treatment
of upgradient contamination within the first 3 years, but tests conducted
within the PRB found a decrease of hydraulic conductivity by two orders
of magnitude, due to the biopolymer (i.e., guar gum) applied during excavation of the barrier. This stimulated the microbial activity of sulfate reducers