Environmental Engineering Reference
In-Depth Information
Since the erection of the full-scale PRB, no further information, especially
no data regarding performance/cleanup efficacy have been published. It is
believed that the PRB does not work as expected, probably because of a loss
in permeability due to the accumulation of hydrogen gas within the ZVI bed
at several gates, thus plugging the pores of the bed and perhaps rendering it
impermeable.
13.2.2.5 Karlsruhe
A full-scale F&G equipped with GAC was erected in Karlsruhe in 2000/2001
to treat PAHs and BTEX (Schad et al., 2000; Birke et al., 2003, 2010; Burmeier
et al., 2006). The site is located in the Rheine valley. During 79 years of opera-
tions, the former gas works plant had produced town gas, coke, tar, benzene,
and ammonium sulfate from more than 4.3 million tons of coal in total. Soil
and groundwater had been contaminated by PAHs and BTEX during that
time, mostly because of several tar oil spills. A large PAH plume (about 200 m
wide and 400 m long) stretching toward the city center of Karlsruhe origi-
nates from the property (covering around 100,000 m
2
). There was a partly
accompanying vinyl VC plume, although its source was not definitively iden-
tified as yet (this plume originates upgradient of the site). Maximum con-
tamination levels detected were 500-600 μg/L of PAHs (acenaphthene is the
main component), 20 μg/L of benzene, and 2 μg/L of ammonium, whereas
VC could be detected at up to 100 μg/L. The local aquifer is approximately
12 m thick consisting of sandy, densely bedded gravel, which is underlain
by a clay layer at a depth of 16 m below the ground level. The groundwater
flow rate was determined at about 12 L/s under natural conditions. A full-
scale F&G barrier charged with about 150 tons of GAC in total, for which
regeneration cycles of 5-15 years were expected (depending on the concen-
tration of the contaminants), was planned and eventually set up in January
2001. The Karlsruhe PRB is about 240 m long and 17 m deep, arranged in an
almost straight line, along which eight, nearly equidistant gates are posi-
tioned. The funnel consists of sheet piles that were pressed, not driven, into
the ground using the “silent-piler-technique” to prevent damage to nearby
buildings and gas supply pipelines. The gates consist of specifically perfo-
rated, cylindrical steel tubes that were set into the ground by means of large-
diameter borings. Setting up the gates commenced by driving cylindrical,
large-diameter (2.5 m) borehole casings (circular caisson installation) into
the ground and excavating them to a final depth of 15-17 m below ground
level (0.5 m below the aquifer base). Prefabricated, cylindrical gate segments
were connected to each other and the whole construction was lowered into
each shaft/borehole (≈ 18 m in length and 1.8 m in diameter). Monitoring
wells were installed at the inflow and the outflow of the gates. Pea gravel was
used as a filter medium to homogenize the flow of water through the gates,
and loaded in front of and behind each gate. The central section of each gate
was loaded with GAC. The total cost amounted to more than 4 million €; over
Search WWH ::
Custom Search