Environmental Engineering Reference
In-Depth Information
Manipulation of pH can change the nature of the assimilative capacity soils, as stated
previously. It addresses the precipitation of heavy metals in solution (porewater) or disso-
lution of precipitated heavy metals. Changes in pH of the soil-water system will produce
changes in the sign of surface electrostatic charges for those soil materials with ampho-
teric surfaces, i.e., surfaces that show pH-dependency charge characterization. Subsoils
containing oxides, hydrous oxides, and kaolinites are good candidates for pH-dependent
charge manipulation. Changes in surface charge characterization can result in increased
bonding of metals or release of heavy metals from disruption of bonds. Both pH and
Eh
changes will have considerable inluence also on acid-base reactions and on abiotic
and biotic electron transfer mechanisms. Abiotic transformations of organic chemical
contaminants due to acid-base and redox reactions are minor in comparison to biotic
transformations.
10.7.2 NA Treatment Zones for Impact Mitigation
Treatment zones are regions in the subsoil that utilize the NA process tool, and more
speciically, enhanced NA, to attenuate the impact of contaminants during transport
in the subsoil. Since it is rare to ind source discharges conveniently located directly
in a region where the various elements contributing to natural attenuation capabilities
are available, the usual procedure is to provide a treatment zone that would capture
the contaminant plume during transport. A good knowledge of site hydrogeology is
essential for this type of mitigation procedure to function properly. Figure 10.14 shows
Receptors
Enhanced NA as
treatment zone
Contaminant plume
Contamination source
Plan view
FIGURE 10.14
Simpliied plan view of a treatment zone established with enhancement of the natural attenuation capability of
the site subsoil to mitigate impact of contaminants on land environment and to protect
receptors
.
Search WWH ::
Custom Search