1. Classification of remediation for contaminated soil
The contamination of soil and groundwater is said to be accumulating incessantly. Unless the contaminants are completely degraded or removed in situ, the pollution state is not solved. As measures for the remediation of soil contamination, various technologies are currently being developed and applied in practical use, including the investigation technique. However, the procedures need more time and bigger budget. Conversely, soil and groundwater remediation has already been materialized as a form of business in Europe and America. As estimated based on the results of the investigation technique and from the remediation records in Japan, it is likely to cost trillions to 10 trillions yen on the market scale.
Innovative remediation technology has been developed centering on the superfund sites, especially in the U.S. The pioneering technology has been introduced to Japan and the technology suitable for local scenario and social economic situation of the country has been developed. Recently, manuals and laws in relation to soil and groundwater contamination have been approved. Simultaneously, they boost the development of technology for the remediation of polluted soil and groundwater.
The occurrence of soil and groundwater pollution varies and depends greatly on the process of soil formation or by different areas. The contaminants follow the course of water movement, which is dependent on the geology or the particular chemical properties of the substances. Therefore, an absolute remediation technology does not exist. Furthermore, a single technology is not enough to treat the same polluted spot from the early to the final stages.
Under such circumstance, the countermeasure technology, which has been utilized for the soil and groundwater contaminated places in Japan, can be classified in general into five elemental technologies shown in Fig. 1. The technology shown in Category A confines contaminants in situ or stabilizes them using certain medication. Although it prevents contaminants from diffusing into water, they remain in situ. Category B is the technology wherein contaminants are degraded chemically and biologically in situ. Meanwhile, Category C is the removal of contaminants in-situ by extracting the soil gas containing volatile contaminants and subsequently siphoning groundwater.
On the other hand, Category D is the technology in which contaminants is excavated and the 3 phases of soil, soil gas, and soil water are removed simultaneously. Even though this technology can be classified into the remediation technology like Category B or Category C, it is necessary to remove contaminants from the excavated soil or to detoxify the soil. The technology of treating contaminants extracted by these measures is classified under Category E. In like manner, various technologies are also developed according to the properties of the contaminants or the grade of contamination.Examples of such technologies are decomposition by solidification and stabilization, vitrification, thermal treatment, redox, and ex situ biotreatment.