Environmental Engineering Reference
In-Depth Information
large number of gaseous substances of interest and mixtures can be detected
by sensors or on-site analyzers. Small diameter (25 mm) soil gas probes are
installed at specified depths by direct push or manual electric ramming.
Low low pumping and on-site analysis is the preferred sampling method.
In situ diffusive sensors are available; however the absorption rates are not
as consistent or reliable.
Gas sensing and sampling near the capillary fringe can support the esti-
mation of gas distribution and propagation in the groundwater zone. The
initial signals of soil gas sensors are interpreted as breakthrough times
and possible locations of gas emission from the groundwater domain. Soil
gas sensors are used to check the sealing result of grouted injection lances.
Additionally, gas consumption (e.g., oxygen, methane) or production (e.g.,
carbon dioxide) can be estimated by soil gas sampling, and the unsaturated
zone can be included into an RGBZ treatment system (Uhlig, 2010).
10.3.4 Techniques for PRB Performance Control
Once reactive gases are dissolved into the groundwater flow, there are sev-
eral measures or techniques that can be used to evaluate and control trans-
port and the in situ transformation of dissolved compounds in the aqueous
phase. These methods can also evaluate the interactions with reactive sedi-
ment surfaces (ENA). Sophisticated reactive modeling tools and techniques
for site characterization and the identification of transformation process are
also available. A number of these techniques require a site and contamina-
tion-specific application.
Given all of the possible methods to control the reactive zones of gas PRBs,
an algorithm was constructed to take into account adaptive performance
and optimization measures, and evaluated at the BIOXWAND gas PRB. The
algorithm is site specific and given as an example in Table 10.2.
10.4 Example Applications of the RGBZ Technology
Three example applications have been chosen to demonstrate the capabili-
ties of gas PRBs. First, the results of a full-section PRB (BIOXWAND) that
has been operating for 5 years to treat an ammonium plume are presented.
A homogenized nitrification effect was reached using injections of variable
oxygen gas and air concentrations. The PRB was scaled up to a length of
800 m. In the second example, an oxygen gas PRB was used to naturally
attenuate an organic contaminant plume containing aliphatic and aromatic
hydrocarbons. The PRB technology has been accepted by the mining indus-
try and environmental authorities as a method that can be used to prevent
the future plume propagation or deviation due to mining activities using
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