November 27, 2003
The Ministry of the Environment has put together the results of groundwater quality monitoring conducted by the national and local governments in FY 2002 pursuant to the Water Pollution Control Law.
The Water Pollution Control Law provides that the governor of a prefecture shall monitor the quality of groundwater. In accordance with the groundwater quality monitoring program prepared annually by each prefecture, the national and local governments monitor the quality of groundwater.
1. Results of general monitoring survey
The overall condition of groundwater pollution is evaluated based on the result of the general monitoring survey. In FY 2002, the survey was conducted on 5,269 wells in 1,768 municipalities.
Table 1 shows the monitoring results. Among the 5,269 wells surveyed, 351 wells have one or more items exceeding the environmental quality standards (EQSs). The proportion of wells exceeding the EQSs is 6.7% (7.2% in FY 2001). In terms of the substances most commonly found to exceed the EQSs, nitrate nitrogen and nitrite nitrogen is the highest at 5.9% (5.8% in FY 2001). It is followed by arsenic at 1.5% (1.3% in FY 2001) and fluorine at 0.4% (0.7% in FY 2001). No wells are found exceeding the EQSs of the other 13 items including cadmium.
Table 2 shows the changes in the rate of exceeding the EQSs in general monitoring surveys conducted after establishment of the EQSs.
2. Items with the high rate of exceeding the EQSs
Fig.1 shows the transition of the rate of exceeding the EQSs regarding five items with the highest rate. Compared to other items, nitrate nitrogen and nitrite nitrogen shows the higher rate of exceeding the EQS. Arsenic and fluorine can sometimes be detected in groundwater due to natural causes such as elution from rocks and soil. Trichloroethylene and tetrachloroethylene, whose main pollution sources are factories, show a downward trend in the rate of exceeding the EQSs.
When a well supplying drinking water is found to be polluted, the local government provides guidance to well users in order to prevent health damages.
3. Pollution of groundwater by nitrate nitrogen and nitrite nitrogen
Nitrate nitrogen and nitrite nitrogen is designated as one of the monitoring items in 1993. The EQSs of it was set in February 1999. Surveys of these items have been conducted since FY 1999 in accordance with the Water Pollution Control Law. Since then, it has shown the high rate of exceeding the EQSs. Table 3 shows the survey results of nitrate nitrogen and nitrite nitrogen by prefectures in the general monitoring survey. While there are relatively many wells in Hokkaido and Kanto region that exceed the EQS, no wells in Hokuriku and Chugoku regions exceed the EQS.
|Note:||The monitoring items are substances that may affect human health, but water quality survey results of public waters do not indicate a need for immediate establishment of the environmental quality standards (health item). It is recognized, however, that further accumulation of information on the substance is required.|