Reactive (Oxygen) Gas Barrier and Zone Technologies - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 192

filter tubing; (4) an appropriate pressure, diffusion, and reaction-resistant cas-
ing or tubing material; and (5) a gas filter backfill construction that permits
homogeneous horizontal gas flow coupling to the subsurface layers.
Drilling Injection Lances (BIL) can be installed in heavy or variable layered
sediment and bedrock environments using dry and hydraulic drilling using
diameters <250 mm. There are typically no depth restrictions and multilevel
injection filters can be positioned in one borehole (Schinke, 2008). The main
disadvantage is that the extraction of subsurface material up to 2 m in diam-
eter cannot be avoided (Engelmann et al., 2004). Following the installation
of lances, the measurement of material extraction during the drilling pro-
cess and tight grouting of the casing annulus and the loosening zone are
required, even under bedrock conditions. Special grouting valve casings are
available for high-pressure injection of sealing suspensions (e.g., bentonite
clay). Injection volumes must be balanced and controlled, and a multistep
grouting procedure has to be planned with intermittent testing of the seal-
ing effect. Care has to be taken during grouting, as undesired clogging of the
main gas transport layers or gas filters can occur. Suffusion-protected gas fil-
ter zones are built-up by gravel or coarse sand. Gas injections via multilevel
filters can be performed using casing packers.
There are three types of Sounding Injection Lances . During direct-push
installation, displacement and compaction of the rock material take place,
and an autosealing effect is gained between the casing and the borehole
walls. Borehole diameters are approximately 30-80 mm.
Percussion Sounding Injection Lances (RIL) can be installed in sediments to
a depth of 10 m using 2-3 in casings (e.g., HDPE) with a filter tip and seal-
ing packers between the casing segments (Figure 10.6—RIL-type A). The
casing remains in the borehole and gas injection tubing and gravel fillings
are placed into the filter zone, which is sealed by a compacted clay layer. In
addition, sensors and multilevel filters can be installed. RIL are installed in
medium-compacted sediments using heavy pneumatic percussion tools (e.g.,
Geoprobe ® , up to 100 kN). Depths of 30-40 m can be reached, although care
must be exercised when pushing down a cone tip with fixed injection tubing
as the milling of soil material can lead to filter sealing or destruction. After
reaching the planned depth, the hollow casing is drawn back and can be
used multiple times. An additional hollow drilling auger can help to lower
the penetration resistance of highly compacted or very coarse layers by pre-
loosening. High pressure sealing of the borehole can be done during with-
drawal of the casing (Figure 10.6—RIL-type B). It is recommended that up to
2 months consolidation time be given for the installed lances before starting
lance operation, particularly for HDI applications (Engelmann, 2010).
Continuous hydraulic cone penetration tools (CPT) with up to 200 kN are
used to install Penetration Injection Lances (DIL). Thinner casing walls allow
for the installation of larger diameter tubing. The maximum depth is in the
same magnitude as for RIL and predrilling or stabilizing casings are required
in heavy soil layers. A filter casing injection lance (Figure 10.6—DIL-type B)