Spread of Groundwater Contamination and Countermeasures - Mito City, Ibaraki Prefecture, Changes from 1997 to the 2020s

Spread of Groundwater Contamination and Countermeasures - Mito City, Ibaraki Prefecture, Changes from 1997 to the 2020s

### Beginning of the 1990s
In 1997, groundwater contamination became serious throughout Japan. Particularly in the Kanto Plain, contamination was noticeable around former factory sites and industrial waste disposal sites. Major contaminants included hexavalent chromium and chlorinated organic compounds such as trichloroethylene and tetrachloroethylene, which raised concerns about health hazards. In the Tama area of Tokyo, a survey was conducted to identify the source of contamination, and it was found that more than 70% of the pollution originated from illegal waste. In addition, Kumamoto City installed a groundwater monitoring system and began regular analysis of heavy metals and organic compounds. Air stripping and activated carbon adsorption methods were introduced as purification technologies, and a 5 billion yen purification project was implemented in the Chubu region.

### Development in the 2000s
In the 2000s, measures to deal with groundwater contamination spread nationwide, and purification technology advanced. 2004, in Tajimi City, Gifu Prefecture, the concentration of hexavalent chromium exceeded 0.3 mg/L (six times the standard value), and purification work was carried out. In this project, soil cleaning technology and bio-remediation (purification using microorganisms) were combined, and the concentration was reduced to below the standard level in about three years. Also in 2008, trichloroethylene contamination in Nagoya's Minato Ward drew attention, and facilities were installed to treat 100,000 tons of groundwater per year. The number of observation wells nationwide has also been expanded to more than 2,000, enabling real-time monitoring.

### Innovations and International Expansion in the 2010s
The 2010s saw further innovations in groundwater contamination control: in 2013, electrochemical decomposition technology was employed to treat benzene contamination in Numazu City, Shizuoka Prefecture, reducing the concentration to 0.02 mg/L (below the standard value) in just one year. In Kumamoto City, PFAS (perfluoroalkyl compounds) were also detected, and a new advanced purification facility was constructed. In this facility, activated carbon adsorption and reverse osmosis (RO) membranes were introduced, achieving a removal rate of over 99%. Furthermore, Japanese purification technology has been applied overseas, and a groundwater purification project was initiated in Surabaya, Indonesia. The project has successfully reduced the concentration of heavy metals detected in local factory wastewater to below the standard value.

### Current Status and Prospects for the 2020s
In the 2020s, contamination countermeasures were further strengthened: In 2021, the concentration of hexavalent chromium in Mito City, Ibaraki Prefecture, was 10 times the standard value (0.5 mg/L), and a large-scale soil excavation and chemical injection cleanup was conducted. The project, which cost a total of 1.5 billion yen, resulted in an improvement to below the standard value by 2023. In Nagoya, a trichloroethylene concentration of 3 mg/L (15 times the standard value) was found to be contaminated, and improvement was confirmed after five years of treatment in a 2 billion yen cleanup project. In addition, more than 3,000 observation wells have been installed nationwide, and real-time monitoring of groundwater is evolving. On the technical side, electrochemical degradation and bio-remediation have evolved, and purification costs have been reduced by 30% compared to conventional methods.

### Summary
From 1997 to the 2020s, groundwater contamination remediation has evolved through technological innovation and enhanced monitoring. In particular, the selection of remediation technologies that meet local challenges has contributed to solving problems, and efforts continue to overcome contamination as a side effect of industrial activities. With climate change and new chemical risks emerging, further technological development and international cooperation are required.