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Press Release

Monitoring Results of Groundwater Quality in FY 2004

December 20, 2005

The Ministry of the Environment (MOE) announced the results of groundwater quality monitoring conducted by the national and local governments in FY 2004 pursuant to the Water Pollution Control Law. The 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.

1. Number of municipalities and wells surveyed
In FY 2004, the survey was conducted on 11,851 wells (11,862 in FY 2003) in 1,898 municipalities (2,100 in FY 2003) (Table 1).

2. Result of general monitoring survey
The overall condition of groundwater pollution is evaluated based on the result of the general monitoring survey which aims to hold the overall condition of the local groundwater. Table 2 shows the monitoring results. Among the 4,955 wells (5,129 in FY 2003) surveyed, 387 wells (421 in FY 2003) have some items exceeding the environmental quality standards (EQSs). The proportion of wells exceeding the EQSs is 7.8% (8.2% in FY 2003).

Among the substances most commonly found to exceed the EQSs, nitrate nitrogen and nitrite nitrogen have the highest ratio, 5.5% (6.5% in FY 2002), followed by arsenic, fluoride and tetrachloroethylene. For other 13 substances including cadmium, no wells are found exceeding the EQSs.

When a well is found to be polluted, whether it is supplying drinking water or not, in order to prevent health damages, the local government provides guidance for drinking (usage) to well users including the shift to water supply sources.

3. Number of municipalities in which wells exceeding EQSs are existing
Number of municipalities having wells exceeding the EQSs more than once was 849, out of which nitrate nitrogen and nitrite nitrogen was found in 565 municipalities, followed by arsenic, fluorine, tetrachloroethylene, and trichloroethylene. (Fig. 1)

4. Chemicals of which the EQS exceeding rate is higher
Fig. 2 shows the changes in the EQS exceeding rate regarding top five items. (i.e., nitrate nitrogen and nitrite nitrogen, arsenic, fluorine, tetrachloroethylene, and trichloroethylene). Although tetrachloroethylene and trichloroethylene, which main pollution sources are factories, showed a downward trend since the introduction of underground infiltration prohibition in FY 1989, their ratio is leveling off in several years. For worse, new contamination is still detected. Arsenic and fluorine can sometimes be detected in groundwater due to natural causes such as elution from rocks and soil.

Nitrate nitrogen and nitrite nitrogen is designated as one of the monitoring items in 1993, and added to the list of substances for which EQSs are set in 1999. Compared to the other items, their EQS exceeding rate has been higher, and approximately 200 wells are found to be exceeding EQS. Fig. 3 shows that the pollution has become explicit, since the number of wells surveyed and those exceeding the EQS revealed by regular monitoring survey conducted to the wells that had been found contaminated by the previous year have increased.


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