Institute for Rural Engineering, NARO

Labor saving water sampling method for groundwater dating

-Time required for water sampling is reduced, equipment can be simplified and lightened-

NARO has developed a technique to collect groundwater in a labor-saving manner using a commercially available water sampler for wells in order to measure the age of groundwater. In the dating method with the concentration of sulfur hexafluoride (SF6) as an index, which is a dissolved gas in groundwater, the time required for sampling can be reduced by up to 60 to 70%. Also, this method does not use a pump, hence the survey equipment can be simplified and lightened thereby reducing the burden on investigators.


In order to properly manage groundwater resources in rural areas, we need not only the location information of where the resources such as rainwater infiltrates and converts to groundwater, where it flows and springs, but it is also important to know how much time the groundwater has flowed over. Shallow groundwater used in agriculture and groundwater flowing on slopes in hilly and mountainous areas are characterized by relatively short residence times (few years to around a decade). The method using sulfur hexafluoride (SF6) is effective for dating such young groundwater. While collecting groundwater for dating using this method, in order to avoid the high-concentration of SF6 in the atmosphere from dissolving in the sample water, the water is generally collected with a device such as pump so that the water does not come into contact with the atmosphere. But this method consumes much time to collect water, which caused inefficiency in the survey.

NARO has developed a labor-saving water sampling method using a commercially available water sampler for wells. The time required for sampling can be reduced up to 60 to 70% by this method. In addition, since this method uses the well sampling device and the sampling rope alone, the equipment used can be simplified and lightened, and the work load on the investigator can be reduced. In this method, the sample water comes into contact with the atmosphere during sampling, but the dating accuracy is almost same as the conventional method.

Technical data (PDF format) that summarizes the points to note for this method can be downloaded from the NARO website. This method is useful for efficiently understanding the abundance of groundwater resources in rural areas and the groundwater flow status in sloped areas (landslide areas, etc.) in mountainous areas.

Dating groundwater with sulfur hexafluoride (SF6) using labor-saving sampling method

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Reference Information

Fig.1 Changes in sulfur hexafluoride (SF6) concentration in the atmosphere of Japan
Fig. 2 Water sampler for wells

Fig 3. Water sampling procedure using well water sampler

Fig. 4 Comparison of SF6 concentration and residence time
in groundwater collected by conventional and labor-saving method

Fig.5 Effect of reduction of sampling time by using labor-saving method