column experiments can be used. Columns filled with calibrated sand are used to test
the effect of the porous medium without preferential flows. Although column results
are not representative of the field scale, treatment efficiencies at a heterogeneous site
are generally lower than in controlled columns. However, column studies can be
used to optimize the treatment process through is thus an important prerequisite to
allow an efficient treatment at field scale. Due to the highly variable nature of the
underground, treatment techniques cannot be truly compared at real sites. Some
attempts were done (Cape Canaveral, USA) but, as they were done on different
sources, it was difficult to draw general conclusions (Geotrans 2007). The comparisons done at Hill Air Force Base (USA) on large isolated cells under controlled
conditions showed that the removal efficiency was a consequence of the soil
heterogeneity and no clear comparison of the techniques was possible (McCray
et al. 2011). Similarly, Brooks et al. (2008) reported remedial efficiency at two sites,
and Barnier et al. (2013) used two sources at the same site, but both could not strictly
compare the efficiency of the techniques, these being done on different source zones.
For this purpose, trials at the tank scale can be done, but they require much more time
and equipment than columns. The advantage of the tank scale is that it can include
one set of controlled heterogeneity to understand the behavior in the field.
For chemical oxidation, batch experiments have shown high BTEX removal rates
(Crimi and Taylor 2007; Anhua et al. 2014). Fenton’s reagent was an efficient
oxidant in batches (Crimi and Taylor 2007) but also in Diesel-contaminated columns
(Stuart et al. 2001). In columns, Fenton’s reagent or persulfate oxidation led to the
low removal rate for Polycyclic Aromatic Hydrocarbons (PAHs) (Lemaire et al.
2013). One important issue of Fenton injection on field sites is the explosion hazard.
Therefore, developments were done to use pulsed injection (Watts et al. 2014) or to
use peroxide alone, but this requires the presence of iron in the solid phase
(Ravikumar and Gurol 1994). Permanganate is classically used for chlorinated
solvents and also for hydrocarbons except benzene (Crimi and Taylor 2007). That
is the reason why it was not selected in this study. Persulfate use is more recent
(Siegrist et al. 2011). Its temporal stability allows to reach zones that are distant from
the injection area. Ozone is much less common, but proved to be efficient at the
column scale (Choi et al. 2002).
At Borden, Hood (2000) showed that permanganate injection close to a small
emplaced source zone for 1.5 years reduced more than 90% of the PCE/TCE mass
flux. The amount of NAPL mass removed could not be assessed due to uncertainty in
sampling. Thomson et al. (2008) tried oxidation of PAHs but this did not modify the
long-term release of these products, although the added amount of oxidant should
have removed all PAHs. Mackinnon and Thomson (2002) showed a 45% removal of
PCE as NAPL by oxidation in a 2D tank despite quite high (1 mg L
À1 ) residual
concentration downgradient the source. Schnarr et al. (1998), adding approx. 6 pore
volumes (PV) of a 10 g L
À1 permanganate solution, oxidized more than 90% of a
PCE source at 8% residual saturation. However, under the same conditions but with
a naturally released source of 8 L of PCE, only 62% of the source could be removed.
Surfactant injection was among the most studied technique in column experiments. As a very high increase in solubility can be reached for chlorinated solvents,
4 Comparing the Efficiency of Oxidation, Sparging, Surfactant Flushing, and. . .
213
the effect of the porous medium without preferential flows. Although column results
are not representative of the field scale, treatment efficiencies at a heterogeneous site
are generally lower than in controlled columns. However, column studies can be
used to optimize the treatment process through is thus an important prerequisite to
allow an efficient treatment at field scale. Due to the highly variable nature of the
underground, treatment techniques cannot be truly compared at real sites. Some
attempts were done (Cape Canaveral, USA) but, as they were done on different
sources, it was difficult to draw general conclusions (Geotrans 2007). The comparisons done at Hill Air Force Base (USA) on large isolated cells under controlled
conditions showed that the removal efficiency was a consequence of the soil
heterogeneity and no clear comparison of the techniques was possible (McCray
et al. 2011). Similarly, Brooks et al. (2008) reported remedial efficiency at two sites,
and Barnier et al. (2013) used two sources at the same site, but both could not strictly
compare the efficiency of the techniques, these being done on different source zones.
For this purpose, trials at the tank scale can be done, but they require much more time
and equipment than columns. The advantage of the tank scale is that it can include
one set of controlled heterogeneity to understand the behavior in the field.
For chemical oxidation, batch experiments have shown high BTEX removal rates
(Crimi and Taylor 2007; Anhua et al. 2014). Fenton’s reagent was an efficient
oxidant in batches (Crimi and Taylor 2007) but also in Diesel-contaminated columns
(Stuart et al. 2001). In columns, Fenton’s reagent or persulfate oxidation led to the
low removal rate for Polycyclic Aromatic Hydrocarbons (PAHs) (Lemaire et al.
2013). One important issue of Fenton injection on field sites is the explosion hazard.
Therefore, developments were done to use pulsed injection (Watts et al. 2014) or to
use peroxide alone, but this requires the presence of iron in the solid phase
(Ravikumar and Gurol 1994). Permanganate is classically used for chlorinated
solvents and also for hydrocarbons except benzene (Crimi and Taylor 2007). That
is the reason why it was not selected in this study. Persulfate use is more recent
(Siegrist et al. 2011). Its temporal stability allows to reach zones that are distant from
the injection area. Ozone is much less common, but proved to be efficient at the
column scale (Choi et al. 2002).
At Borden, Hood (2000) showed that permanganate injection close to a small
emplaced source zone for 1.5 years reduced more than 90% of the PCE/TCE mass
flux. The amount of NAPL mass removed could not be assessed due to uncertainty in
sampling. Thomson et al. (2008) tried oxidation of PAHs but this did not modify the
long-term release of these products, although the added amount of oxidant should
have removed all PAHs. Mackinnon and Thomson (2002) showed a 45% removal of
PCE as NAPL by oxidation in a 2D tank despite quite high (1 mg L
À1 ) residual
concentration downgradient the source. Schnarr et al. (1998), adding approx. 6 pore
volumes (PV) of a 10 g L
À1 permanganate solution, oxidized more than 90% of a
PCE source at 8% residual saturation. However, under the same conditions but with
a naturally released source of 8 L of PCE, only 62% of the source could be removed.
Surfactant injection was among the most studied technique in column experiments. As a very high increase in solubility can be reached for chlorinated solvents,
4 Comparing the Efficiency of Oxidation, Sparging, Surfactant Flushing, and. . .
213