Permeable Reactive Barriers in Europe - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 290

original pumps were then successfully replaced by another type of pump.
Owing to these problems, the effort required for proper O&M of the sys-
tem was much higher than expected. Originally, the test period was planned
only for 1 year. To obtain a sufficient operation period under optimum con-
ditions, the test phase was extended until September 2009 (around 2 years
in total). It was subsequently decided that the system would be extended by
longer funnels and (probably) a second gate for a full hydraulic containment
of the site (Tiehm et al., 2008; Weingran et al., 2009, 2011; Birke et al., 2010;
Birke and Burmeier, 2012a).
13.2.2.7 Rheine
In 1998, a pilot-scale CRB containing two types of ZVI in two separated
segments (total length: 22.5 m) to treat cVOCs (mainly PCE, in 1998: around
10,000 μg/L, in 2012: around 2000 μg/L yet), was installed approximately
400 m downstream from a former dry-cleaning facility located in the small
town of Rheine, about 30 km westward of Osnabrück (Ebert et al., 2001,
2007; Birke et al., 2003, 2004; Parbs and Birke, 2005; Burmeier et al., 2006;
Birke and Burmeier, 2012a,b). Long-term monitoring of the performance
of the PRB was an important part of the mission of the RUBIN network
(RUBIN, 2014): the PRB was extensively used for regular in-depth monitor-
ing campaigns over 12 years (2000 until 2012) including coring both ZVI
types and groundwater modeling to determine performance and predict
the long-term effect (Ebert et al., 2001). The Rheine pilot CRB is 22.5 m long,
0.6-0.9 m thick, and about 6 m deep. A single row of overlapping boreholes
(diameter 0.9 m) was constructed by utilizing caisson installation; these
were then filled with ZVI.
Two types (brands) of ZVI were employed: on the right side (viewed
from upstream), the boreholes were loaded with 69 tons of granular iron
(“Gotthart-Maier”) mixed with pea gravel at a 1:2 volume ratio (34.5 tons each
of iron and gravel) over a length of 10 m. Eighty five tons of “iron sponge”
(ReSponge ® , brand of Mull und Partner GmbH, Hanover, Germany) were
applied on the left side (12.5 m long). A concrete-filled borehole separates the
two segments. The name “iron sponge” is due to the material's appearance:
the small, dark gray or black pellets (average diameter about 1 cm, Birke
et al., 2004; Parbs and Birke, 2005) resemble a pumice-like material. They
consist of reduced iron oxide and were supplied by the steelworks “ISPAT”
(now Mittal Steel), Hamburg, Germany.
Monitoring results prove an effective performance of the ReSponge sec-
tion over the whole PRB life span since 1998, with an overall degradation
efficacy >99.5% while no decrease in reactivity has been indicated. In con-
trast to the efficient iron sponge section, the section containing a mixture of
Gotthart-Maier ZVI and pea gravel showed significantly decreased reactiv-
ity only 6 months after installation. Its initial degradation efficacy for PCE
was >98% decreasing to approx. 80% 1 year after installation. Since then, the