Environmental Engineering Reference
In-Depth Information
Figure 3.3
Macroscale: Hazardous waste site showing spatial heterogeneity of
contamination.
bioremediation at a site. Table 3.2 lists the phenomena influencing bioreme-
diation at each level of observation. It is important to note that observations
made at one scale may not apply to another scale. For example, field-mea-
sured half-lives tend to be longer than laboratory-measured values. This
variance may be caused by the impact of any or all of the limiting factors at
each level of observation on the overall system. For example, the microscale
may be limited by a low concentration of degrading microorganisms,
whereas at the mesoscale, a low-porosity soil (such as a tight clay) may limit
the ability of the microorganisms to reach the contaminant. Furthermore, the
heterogeneity of the site (e.g., multiple types of contaminant and the inter-
jection of clay lenses in a silty sand) may be the limiting factor at the mac-
roscale. Therefore, it is necessary to consider each scale of observation prior
to developing a full-scale remediation design.
3.7 Conclusions
For a remediation design to be successful, the limiting factors at each scale
must be identified so that their impacts can be minimized as much as pos-
sible. This evaluation involves an iterative process. However, sometimes a
limiting factor cannot be changed; e.g., the presence of multiple types of
contaminants or the optimization of a limiting factor may cause another
parameter to become limiting. The iterative process can demonstrate
whether a treatment technology, such as
in situ
bioremediation, is cost effec-
tive for a site. It is easier to tailor a treatment technology to a site rather than
