Remediation: Techniques and Cost - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 389

Ex situ technologies (515) 53% In situ technologies (462) 47%

Soil vapor extraction (248) 26%

Physical separation (21) 2%

Incineration (on-site) (42) 4%

Bioremediation (60) 6%

Bioremediation
(53) 5% Thermal

desorption (71) 7%

Multi-phase
extraction (46) 5%

Incineration (off-site)
(105) 11%

Solidification/
stabilization (44) 5%

Solidification/
stabilization (173) 18%

Chemical
treatment (20) 2%

Other ex situ (43) 4%

Flushing (17) 2%

Chemical treatment - 9
Neutralization - 7
Soil vapor extraction - 7
Soil washing - 6
Mechanical soil aeration - 4
Open burn/open detonation - 4
Solvent extraction - 4
Phytoremediation - 1
Vitrification - 1

Thermal treatment (14) 1%

Other in situ (20) 2%

Neutralization - 8
Phytoremediation - 6
Mechanical soil aeration - 3
Vitrification - 2
Electrical separation - 1

FIGURE 11.13
Soil remediation techniques at 978 CERCLA Superfund sites. (From USEPA, Treatment Technologies for Site
Cleanup: Annual Status Report , 12th edn. EPA-542-R-07-012. Office of Solid Waste and Emergency Response.
Washington, DC, 2007.)

The three most important controlling factors governing the selection of the most efficient
soil remediation technologies employed are (1) cost, (2) the geological environment where
the contaminants reside, and (3) the physical chemistry of the contaminants. Another
important factor is whether a mixture of different types of contaminants and geology
exists. If the geology, contaminant type, and distribution are straightforward (e.g., they
lack synergy), selecting an appropriate soil remedial technology is a simpler task. It is also
important to evaluate whether the contaminants are classified from a regulatory perspec-
tive as hazardous or nonhazardous because this distinction routinely plays an important
role in the selection of a remedial technology. For instance, if a contaminated mass of soil
is classified as hazardous, the disposal cost at a landfill licensed to accept the soil is consid-
erably more than for soil classified as nonhazardous. In this situation, other technologies
would be considered due to the increased cost of transporting and disposing a hazardous
waste.
Figure 11.14 shows the relationship between uniform geology, soil remediation technol-
ogy, and hazardous and nonhazardous classification for VOCs (Rogers et al. 2009). As
indicated by the horizontal dotted line, if the soil volume is less than 5000 tons, soil exca-
vation is the preferred remedial option. When soil volumes are greater than 5000 tons, the