Environmental Engineering Reference
In-Depth Information
Connelly, Chicago, USA) is used for cVOCs (mainly TCA, TCE, and PCE) deg-
radation. 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 hydrau-
lic 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, signifi-
cant 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 fur-
ther 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 concentra-
tions 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, how-
ever, a part of the plume that migrated around the barrier, hydraulic con-
ductivity 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 excava-
tion of the barrier. This stimulated the microbial activity of sulfate reducers
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