Permeable Reactive Barriers in Europe - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 298

soil. Treated groundwater flowed by gravity to the recharge gallery formed
by two trenches filled with gravel approx. 10 m long and 1.0 m wide, to the
depth of impermeable clay. This helped minimize pressure losses of ground-
water flowing by gravity through the system and thus maximize the capture
zone of the drainage trench. A reactive segment was constructed as an in situ
bioreactor. The reactor was designed as a box measuring 2.0 × 1.2 × 4.8 m.
The first chamber (Chamber I) was equipped with an aeration segment at
its base. This chamber had an internal size of 0.9 × 1 m; the water column
fluctuated between 3.2 and 3.6 m (depending on hydrological conditions).
The effective volume of Chamber I varied from 2.98 to 3.28 m 3 (average
3.13 m 3 ). Treated water flowed by gravity from the first chamber to the sec-
ond and third chambers (Chambers II and III). These chambers were con-
nected in parallel and both were equipped with a biofilter unit of 0.5 m 3 . The
filter of the second chamber was filled with “Keramzit” (ceramic granulate
of LIAPOR, Lias Vyntirov, Czech Republic); the filter of the third chamber
contained oxyhumolite (derived from the Vaclav mine near Duchcov, Czech
Republic), with limestone (Vapenka Certovy schody, Czech Republic) as a
pH buffer, and with gravel. Bullet valves regulated the water inflow into
Chamber I and also its discharge to Chambers II and III. Piezometers were
used to monitor the groundwater level in the drainage trench and the indi-
vidual chambers, as well as in both the arms of the recharge gallery. They
were also used for water sampling in all the chambers.
Pilot testing started in January 2004 and continued for 1 year. Tracer tests
were performed to measure groundwater flux through the bioreactor segment
under the current hydrological conditions and to determine retention times
in the individual chambers of the in situ bioreactor; chemical and microbio-
logical monitoring of decontamination effectiveness was also carried out.
Organic contaminants were removed with very high efficiency by the
PRB biofiltration system. This varied from 20.5% to 97.5% in Chamber I.
The lowest efficiency, 20.5%, was achieved for naphthalene; the highest effi-
ciency, above 90%, was observed for BTEX (97.5%), TPH (96.2%), and nitro-
derivatives (90.8%). A high decrease was also detected for other organic
contaminants; chlorinated benzenes (86.6%), TCE (78.6%), and phenols
(73.3%). In the case of Chamber II, a decrease of 9%-93% was observed.
The lowest efficiency was achieved for the removal of TPH (8.7%), naph-
thalene (30.9%), and phenols (43.5%); other parameters showed a decrease
above 50%; TCE of 56.7%, chlorinated benzenes of 71.7%, nitro-derivatives
of 76.8%, and BTEX of 92.9%. Chamber III showed good efficiency in the
range of 35%-98%. The lowest efficiency was observed for naphthalene
(35.4%) and phenols (48.5%); other organic parameters showed decreases
higher than 50%; chlorinated benzenes 61.4%, TPH 56.8%, TCE 52.5%, BTEX
98.2%, and nitro-derivatives 94.7%.
Along with chemical analyses of inorganic and organic contaminants,
the total number of aerobic culturable psychrophilic bacteria in groundwa-
ter and the mineral nutrient content (N, P) were also measured. The results