2.3.3 Combined Vapor Extraction/Groundwater Extraction
The vapor extraction/groundwater extraction process combines two techniques:
venting, and groundwater pumping (Fig. 2.14). This technique aims to pump the
contaminated water (with the objective to treat it), and dewater the capillary fringe so
that the soil vapors can also be extracted and treated. If applicable, this technique is
used only once almost all of the pure product has been pumped out (USEPA 1996;
Sale 2001).
This remediation technique produces higher purification yields than
conventional pumping/skimming because volatilization and associated biodegradation are the main elimination mechanisms of light oil hydrocarbons
(Peargin 1995).
The advantages and drawbacks of this treatment are reported in Table 2.6.
Table 2.5 Advantages and drawbacks of free product recovery with skimming
Advantages
Drawbacks
• Technique is reliable and proven
• Relatively simple and fast treatment
• Does not require water pumping
• Minimizes water recovery and treatment,
which limits operating costs
• Significant water table depth variations are not
a major obstacle for proper operation
• If necessary, the technique can be used in
conjunction with groundwater pumping
• In terms of recovery wells, causes little soil
disturbance, and can be used underneath
buildings
• Recovery wells can be tens of meters deep if
necessary
• Technique does not allow for gaseous and
dissolved phases to be treated (apart from
displacing the phase equilibrium between
vapors and liquids)
• Not suited for recovery of free product less
than 1 cm in thickness
• Technique is applicable when the hydraulic
conductivity is greater than 10
À6 cm s
À1
(to ensure sufficient pure product recovery in
the skimmer)
• The trench must be dug several meters under
the lowest water table level; trenches with
interior depths greater than 7 m often require a
specific excavation process
• Treatment time is longer than with other pure
product recovery techniques (active techniques)
• Remediation yields are lower than those
obtained through other treatment techniques
• Local environments may make it more difficult to dig trenches (piping, hard rock, consolidated sediments)
• Additional recovery operation may sometimes be necessary, as recovering only free
product implies that residual contamination
immobilized into the soil matrix, and present in
the dissolved and gaseous phase, is not treated,
and residual contamination may later become
mobile again (rebound effect)
Compiled from USEPA (1996, 1997a, b, 1999), Suthersan (1997), Colombano et al. (2010)
84
S. Colombano et al.
The vapor extraction/groundwater extraction process combines two techniques:
venting, and groundwater pumping (Fig. 2.14). This technique aims to pump the
contaminated water (with the objective to treat it), and dewater the capillary fringe so
that the soil vapors can also be extracted and treated. If applicable, this technique is
used only once almost all of the pure product has been pumped out (USEPA 1996;
Sale 2001).
This remediation technique produces higher purification yields than
conventional pumping/skimming because volatilization and associated biodegradation are the main elimination mechanisms of light oil hydrocarbons
(Peargin 1995).
The advantages and drawbacks of this treatment are reported in Table 2.6.
Table 2.5 Advantages and drawbacks of free product recovery with skimming
Advantages
Drawbacks
• Technique is reliable and proven
• Relatively simple and fast treatment
• Does not require water pumping
• Minimizes water recovery and treatment,
which limits operating costs
• Significant water table depth variations are not
a major obstacle for proper operation
• If necessary, the technique can be used in
conjunction with groundwater pumping
• In terms of recovery wells, causes little soil
disturbance, and can be used underneath
buildings
• Recovery wells can be tens of meters deep if
necessary
• Technique does not allow for gaseous and
dissolved phases to be treated (apart from
displacing the phase equilibrium between
vapors and liquids)
• Not suited for recovery of free product less
than 1 cm in thickness
• Technique is applicable when the hydraulic
conductivity is greater than 10
À6 cm s
À1
(to ensure sufficient pure product recovery in
the skimmer)
• The trench must be dug several meters under
the lowest water table level; trenches with
interior depths greater than 7 m often require a
specific excavation process
• Treatment time is longer than with other pure
product recovery techniques (active techniques)
• Remediation yields are lower than those
obtained through other treatment techniques
• Local environments may make it more difficult to dig trenches (piping, hard rock, consolidated sediments)
• Additional recovery operation may sometimes be necessary, as recovering only free
product implies that residual contamination
immobilized into the soil matrix, and present in
the dissolved and gaseous phase, is not treated,
and residual contamination may later become
mobile again (rebound effect)
Compiled from USEPA (1996, 1997a, b, 1999), Suthersan (1997), Colombano et al. (2010)
84
S. Colombano et al.