History and Measures of Groundwater Pollution in Tokyo, Ichikawa City, Chiba Prefecture, Koshigaya City, Saitama Prefecture, and Osaka Prefecture - October 2020

History and Measures of Groundwater Pollution in Tokyo, Ichikawa City, Chiba Prefecture, Koshigaya City, Saitama Prefecture, and Osaka Prefecture - October 2020

### 1990s
**Discovery of Groundwater Pollution and Introduction of Legal Measures**
In the 1990s, groundwater pollution became a problem across Japan, particularly in areas such as the Tama region of Tokyo, Osaka Prefecture, and Koshigaya City in Saitama Prefecture. Tetrachloroethylene and trichloroethylene permeated the groundwater, with Koshigaya City recording trichloroethylene levels 10 times the standard at 0.3mg/L. As a result, residents were advised to refrain from using groundwater. In 1997, the government enacted the "Soil Contamination Countermeasures Act" to strictly regulate liquid waste disposal. Dry cleaning businesses and metal processing plants were identified as the main sources of pollution.

### 2000s
**Expansion of Pollution and Strengthened Monitoring**
In the 2000s, groundwater pollution expanded nationwide. In Ichikawa City, Chiba Prefecture, "Toyo Chemical Industries" recorded trichloroethylene levels 10 times the standard, at 0.35mg/L, leading to restrictions on the use of drinking water. In Osaka Prefecture, tetrachloroethylene levels reached 15 times the standard, resulting in similar restrictions. In 2002, the "Act on the Promotion of Proper Chemical Substance Management" was enacted, imposing stricter regulations on industrial wastewater treatment.

### 2010s
**Advances in Purification Technology and New Pollution Discoveries**
The 2010s saw significant advances in purification technology. In the Tama region of Tokyo and Kawasaki City, activated carbon filtration and bioremediation technologies were introduced to purify groundwater. "Kawasaki Technology" invested 50 billion yen in a purification project, reducing trichloroethylene levels below the standard to 0.02mg/L.

### 2020s
**Strengthened Monitoring and New Challenges**
By the 2020s, monitoring systems were reinforced in industrial areas of Tokyo, Ichikawa City, Chiba Prefecture, and Koshigaya City, Saitama Prefecture, enabling real-time tracking of groundwater pollution. However, Toyo Chemical Industries in Ichikawa City continued to record trichloroethylene levels 15 times the standard, and delayed corporate responses remained a concern in some regions.