Soil and Groundwater Contamination Survey and Countermeasure Technologies
| Category of Tchnology | Survey | Soil Gas Survey Method | |
| Media | Soil Gas | ||
| Contaminants |
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| Applied (Demonstrated) Substances | Volatile Chlorinated Organic Compounds | ||
| Scope | Concentration Range | Detecting sensibility is better than 1 ppmv. | |
| Hydrogeological Conditions |
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| Chemical Soil Properties | |||
| Other Remarks | Individual substances cannot be identified by this method, which reduces volatile chlorinated organic compounds such as trichloroethylene to hydrogen chloride for analysis. | ||
| Technology Description | Classification | ||
| Status |
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| Outline of Technology | Gas detection tube method is widely used as a simple method to detect gas leakage. Generally, 100 ml of the subject gas is sampled via a gas detection tube containing detecting agents. The concentration of the subject substance in the gas is read on-site from the change in the color of the detecting agents, measured lengthwise in the tube. In surveying surface soil gas, gas detection tubes are inserted almost to the bottom of small dug holes to obtain the gas via such tubes and to measure the concentrations of contaminants such as trichloroethylene in the gas. | ||
| Required Pre- and Post-treatment | |||
| Enhance Effectiveness through Combination | The soil-gas survey method is used in the line survey method for surveying the plume containing contaminated groundwater and for searching the contaminant source. | ||
| Case History | A survey time per spot ranges from a few to scores of minutes. Although this is a simple, instant survey method, the low detective sensitivity (about 1 ppmv) failed to detect contaminants at spots only about 5 m away from the source of contamination in the recent tests in two areas. In order to detect such contaminant sources, the measuring intervals need to be reduced to about 1/20 of those set for mobilab method or finger-print method that are more sensitive. | ||
| Application Examples | This method has been put to use for examining the soil gas at plants, etc., where the gas is highly contaminated. | ||
| Limitations | A greater part of survey time is used for digging holes, because the concentrations in the gas can be measured on-site. However, due to the low detecting sensitivity, a fairly larger number of spots must be surveyed to get results comparable to those obtained via high sensitivity methods. | ||
| Properties of Treated Soil |
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| Schematic Flow Process | 
Gas Sampling Device and Gas Detection(Takashi Komatsu, Work Environment, Section 6 (5), 1985) |
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| Applicability | In Situ Applicability | Possible | |
| Ground Structures | Applicable even if Ground Structures are Present * | ||
| Required Excavation | Small-diameter (2 cm to 3 cm) holes must be dug to the depth of about 1 m to sample soil gas. | ||
| Groundwater Extraction | None | ||
| Required Space | Space for soil gas sampling work. | ||
| Operational Time |
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| Installation Time | Survey time per spot ranges from a few to scores of minutes if holes are dug easily. | ||
| Maintenance and Control Requirements |
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| Additional Remarks | * Concrete floors must be dug separately by cutters. | ||
| Secondary Impacts to Environment | Secondary Treatment Required? |
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| Effects on Living Environment | |||
| Additives |
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| Possibility of Contaminant Spreading | None | ||
| Secondary By-products |
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Soil Environment Management Division, Water Environment Department, Environmental Management Bureau, Ministry of Environment
Tel: +81-3-5521-8319
E-mail: MOE@env.go.jp
