2.4.1 Free Product Recovery with Groundwater Extraction
and Skimming (Upwelling)
The upwelling technique consists in pumping water above the DNAPL recovery
zone. The cone of depression formed by pumping the groundwater will raise the
DNAPL/water interface level (Villaume et al. 1983; Wisniewski et al. 1985; Ferry
and Dougherty 1986; Cazaux et al. 2014). The process involves using specific
hydrocarbon pumps and dedicated water pumps. These are placed either in the
same recovery well or in two separate wells (Fig. 2.17).
This technique can significantly increase the DNAPL recovery level in the wells.
Recovery flow rates 2–3 times higher than with conventional pumping techniques
have been reported for dimethyl phthalate pollution (Wisniewski et al. 1985).
However, the groundwater pumping rate must be very carefully determined: too
high, and the flow rate will produce emulsions; too low, and the flow rate will not
produce any upwelling.
As a first approach, this phenomenon can be estimated with the Ghyben–Herzberg equation, used to formulate saltwater intrusion in coastal areas (Eq. 2.39).
z ¼
ρ f
ρ s À ρ f
h f
ð2:39Þ
where,
.: thickness of freshwater zone below sea level to a point on the interface (m)
Fig. 2.16 Schematic representation of DNAPL free product recovery [adapted from Colombano
et al. (2010)]
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
89
and Skimming (Upwelling)
The upwelling technique consists in pumping water above the DNAPL recovery
zone. The cone of depression formed by pumping the groundwater will raise the
DNAPL/water interface level (Villaume et al. 1983; Wisniewski et al. 1985; Ferry
and Dougherty 1986; Cazaux et al. 2014). The process involves using specific
hydrocarbon pumps and dedicated water pumps. These are placed either in the
same recovery well or in two separate wells (Fig. 2.17).
This technique can significantly increase the DNAPL recovery level in the wells.
Recovery flow rates 2–3 times higher than with conventional pumping techniques
have been reported for dimethyl phthalate pollution (Wisniewski et al. 1985).
However, the groundwater pumping rate must be very carefully determined: too
high, and the flow rate will produce emulsions; too low, and the flow rate will not
produce any upwelling.
As a first approach, this phenomenon can be estimated with the Ghyben–Herzberg equation, used to formulate saltwater intrusion in coastal areas (Eq. 2.39).
z ¼
ρ f
ρ s À ρ f
h f
ð2:39Þ
where,
.: thickness of freshwater zone below sea level to a point on the interface (m)
Fig. 2.16 Schematic representation of DNAPL free product recovery [adapted from Colombano
et al. (2010)]
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
89