required entry pressure. Free product migrates downward (fingering) until it reaches
an impermeable substratum where it is trapped (provided DNAPL is dense enough).
Initially, free product recovery involves physical removal via vertical or horizontal wells or trenches using specific pumping and skimming equipment similar to that
shown in the previous section (Fig. 2.16) (ITRC 2004). This technique can prevent
mobile DNAPLs from migrating, and allows for a higher contaminant recovery
yield. However, it cannot reach contaminants below residual saturations, without a
thermal- or chemical-enhanced approach. This step will significantly improve the
overall remediation efficiency, particularly as it relates to pumping and treating the
dissolved phase (Huling and Weaver 1996; Kueper and Gerhard 2014). The
pumping can be done until the DNAPL recovery rates fall.
The optimum recovery conditions are those which combine the following factors:
(1) the DNAPL is continuous and has collected in a shallow, impermeable subsurface depression; (2) a permeable aquifer (Cohen and Mercer 1993).
If the amount of DNAPL is substantial, the stakes are significantly higher due, for
example, to potential contamination of the drinking water supply close to the site.
Once the DNAPL recovery rates have decreased significantly, dynamic pumping of
the contaminated groundwater (dissolved phase with water pumps), and DNAPL
(with hydrocarbon pumps), can begin. The pumps are placed in the same recovery
wells as skimmers, or in adjacent wells. This complementary measure creates a
hydraulic confinement and increases pure DNAPL recovery (Schmidtke et al. 1992;
Huling and Weaver 1996; Sale and Applegate 1997; Kueper and Gerhard 2014).
Fig. 2.15 Schematic representation of LNAPL dual-phase extraction (single unit network)
[adapted from Colombano et al. (2010)]
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
87
an impermeable substratum where it is trapped (provided DNAPL is dense enough).
Initially, free product recovery involves physical removal via vertical or horizontal wells or trenches using specific pumping and skimming equipment similar to that
shown in the previous section (Fig. 2.16) (ITRC 2004). This technique can prevent
mobile DNAPLs from migrating, and allows for a higher contaminant recovery
yield. However, it cannot reach contaminants below residual saturations, without a
thermal- or chemical-enhanced approach. This step will significantly improve the
overall remediation efficiency, particularly as it relates to pumping and treating the
dissolved phase (Huling and Weaver 1996; Kueper and Gerhard 2014). The
pumping can be done until the DNAPL recovery rates fall.
The optimum recovery conditions are those which combine the following factors:
(1) the DNAPL is continuous and has collected in a shallow, impermeable subsurface depression; (2) a permeable aquifer (Cohen and Mercer 1993).
If the amount of DNAPL is substantial, the stakes are significantly higher due, for
example, to potential contamination of the drinking water supply close to the site.
Once the DNAPL recovery rates have decreased significantly, dynamic pumping of
the contaminated groundwater (dissolved phase with water pumps), and DNAPL
(with hydrocarbon pumps), can begin. The pumps are placed in the same recovery
wells as skimmers, or in adjacent wells. This complementary measure creates a
hydraulic confinement and increases pure DNAPL recovery (Schmidtke et al. 1992;
Huling and Weaver 1996; Sale and Applegate 1997; Kueper and Gerhard 2014).
Fig. 2.15 Schematic representation of LNAPL dual-phase extraction (single unit network)
[adapted from Colombano et al. (2010)]
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
87