Environmental Engineering Reference
In-Depth Information
the situations leading to contaminant and contaminant loading of the ground surface.
The bottom-left diagram in the igure concerns the problems discussed in Chapter 6. The
land farming scheme shown in the bottom right of the diagram assumes that a prepared
impermeable base is in place before placement of the material to land farmed. Techniques
for land farming will be discussed in a later section when mitigation and treatment alter-
natives are addressed.
The principal issues for contaminant loading of the land surface relate to the transport
of contaminants from the contaminant source. By and large, spills and deliberate dumping
of waste materials involve small suricial areas (i.e., small areas on the land surface). These
will serve as point sources for transport of contaminants into the ground. Surface runoffs
from these regions tend to be small. Meanwhile, surface runoffs for other land applica-
tion of contaminants resulting from deposition of airborne noxious substances and use of
agricultural chemicals (including pesticides) can be serious issues—because of the extent
of the land surface affected. The surface runoffs of contaminants arise if rainfall occurs
or continues before the noxious substances and agricultural chemicals have a chance to
effectively iniltrate or leach into the subsurface. Since the receiving sites for surface run-
offs are topographically lower than the source location, these sites will likely be lowlands,
wetlands, and receiving waters. Contamination of these regions (from surface runoffs) is
commonly identiied as
non-point source contamination
.
Contamination of the subsurface material (subsurface geological material) and the
underlying aquifers from contaminant sources occurs because of the transport of contami-
nants in the subsurface material. Laboratory studies on the transport of contaminants in
soils have been conducted for a large variety of soil types and contaminants. Field studies
have also been performed in support of remediation projects and as due diligence work.
Procedures and analytical-computer models have been developed to provide one with the
capability to determine and/or predict the movement, distribution, and concentration of
contaminants in the subsurface soil. A brief summary of these can be found in Section
2.5.4 in Chapter 2. As also emphasized previously, detailed treatment of these subjects can
be found in textbooks dedicated to the study of contaminant fate and transport in soils.
The discussion of contaminant transport processes and predictions will be found in the
latter portion of this section.
The essential elements required for assessment or evaluation of the impacts from surface
discharge phenomena such as spills from industrial operations and systems such as pipelines
and vehicular trafic transporting liquid wastes or heavy oils and bitumen, dumping, etc.,
are shown in Figure 9.7. In addition to determination of the size of affected area and quantity
of material spilled, discharged, and/or dumped, one is required to determine the following:
1. Nature and composition of the discharged material
2. Hydrogeological setting in the region
3. Subsoil proile, material composition, and properties
4. Transport processes involving the types of contaminants found in the composi-
tional analyses, from laboratory tests
5. Transport and fate of contaminants (emanating from the surface discharge) in the
subsoil, using predictive models and test information on partitioning of contami-
nants and transmissivity characteristics of the contaminants
6. The environmental and biotic receptors and how they will be impacted
7. Source-path-receptor relationships
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