Environmental Engineering Reference
In-Depth Information
solids). Detailed discussion of many of the bonding mechanisms and their reactions to
changes in the immediate environment has been developed in Chapters 2 and 9.
10.10 Engineered Mitigation-Control Systems
As we have indicated at the outset, the use of technological schemes for mitigation and
management of contaminants in the ground is probably best utilized for limited and well-
deined source locations of contaminants. Good examples of these are waste landills,
leaking underground storage tanks, spills and discharges, and containment ponds. Many
of these are shown in the diagram in Figure 2.6 in Chapter 2. Technological solutions for
management and control range from construction of impervious barriers that would inter-
cept the plume to removal of the contamination source and the entire affected region. To
a very large extent, the methods chosen or designed to manage and control contaminant
advance in the subsoil are necessarily site- and situation-speciic. Also, to a large extent,
the nature of the threats posed by the contaminants and the pathways to the various recep-
tors are considerations that will dictate the type and kind of technological solution sought.
Finally, the control-management technological solution sought will always be analyzed
within the framework of risks-reward and cost-effectiveness.
The record shows that there are some very dificult-to-treat contaminated sites. By and
large, these are sites contaminated with organic chemical compounds that are severe
threats to human health. For these kinds of contaminated sites, containment with conin-
ing structures has been constructed. These allow these sites to be isolated while awaiting
effective and economic remediation solutions. In the case of impervious barriers, these
are generally constructed from sheet piles lined in the interior with membranes to deny
lateral advance of the contaminant plume. Dificulties arise in controlling the downward
advance of the contaminant plume when the plume arrives at the lateral impervious bar-
rier. Suggestions range from driving the sheet piles down into an impervious layer as
shown, for example, in Figure 10.19, to injection grouting to develop an impervious base at
some depth in the ground, to inclined-to-horizontal placement of sheet piles using tech-
niques similar to the oil industry for inclined drilling.
If an impervious clay layer can be found directly below the contaminated region, the
methodology shown in Figure 10.19 is probably the most expeditious means for con-
trolling the escape of fugitive contaminants. By and large, for situations such as the one
depicted in Figure 10.19, the contaminants resident in the contaminated site would likely
be various kinds of organic chemicals. Heavy metals associated with these chemicals will
likely be sorbed by the soil solids and will not be very mobile. Hence, the nest of treat-
ment wells sunk into the contaminated region will be geared toward bioremediation of the
organic chemical contaminants. Monitoring wells placed outside the conining sheet-pile
wall, particularly downstream, will provide continuous information on the eficiency of
the containment system. Note that the schematic representation of the nest of wells (treat-
ment and monitoring) is relatively crude. Wells should be placed with varying vertical and
horizontal sampling points and locations. If extra precaution is sought, a treatment zone
using enhanced NA capability as described in Section 10.6.1 outside the conining sheet-
pile wall can be introduced.
For control of contaminant plumes during treatment as part of impact management,
several options are available. It the contaminant source is well delineated and deined,
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