Environmental Engineering Reference
In-Depth Information
15.3. Active containment
in situ
15.3.1.
Pump and treat
This process is partly made
in situ
(for pumping) and partly off-site (for the
treatment). It consists of inducing radial water circulation in the direction of each
point of extraction (see Figure 15.1). This process makes it possible to extract the
polluting substances (organic or mineral) using water. The water is saturated with
dissolved, pure, adsorbed or gas-based pollutants and then treated with one or more
ex-situ
treatment technologies. In this context, pump and treat can be regarded as a
treatment rather than a containment process. However, in terms of
in situ
aspects
and being based on pumping, pump and treat is typically classified as a method of
containment [CLA 98, FRE 97].
It is important to underline the fact that this method of environmental
remediation can also be ineffective. Indeed, the existence of heterogeneities affects
the hydraulic impact of the winding shafts and, consequently, the effectiveness of
pumping. Pump and treat in zones of low permeability is not practical because the
outputs are too low for continuous pumping. In spite of the problems historically
associated with this technique of environmental remediation it continues to be used,
mainly in combination with other techniques [MCK 92]. A relatively new and
successful adaptation is the use of horizontal wells or drains [BER 95, BRE 97, BY
96, HOF 98, REI 94].
Figure 15.1.
Diagram of the pump and treat process [LEB 98]
15.3.2. Reactive barriers (low permeability)
The principal difference between the traditional barriers in containment, such as
trench wall slurry with or without a geomembrane, and the reactive barriers is the
fact that the traditional approach supports the total imprisonment of the site, while
reactive barriers offer the potential to treat the pollutants without the need to
