History and Countermeasures for Groundwater Contamination in Tokyo, Ichikawa City, Chiba Prefecture, Koshigaya City, Saitama Prefecture, and Osaka Prefecture - October 2020

History and Countermeasures for Groundwater Contamination in Tokyo, Ichikawa City, Chiba Prefecture, Koshigaya City, Saitama Prefecture, and Osaka Prefecture - October 2020

### 1990s
**Coverage of Groundwater Contamination and the Beginning of Legal Action**.
In the 1990s, groundwater contamination became a problem throughout Japan, especially in the Tama region of Tokyo, Osaka Prefecture, and Koshigaya City, Saitama Prefecture, where trichloroethylene and tetrachloroethylene seeped into groundwater. In Koshigaya City, Saitama Prefecture, trichloroethylene reached 0.3 mg/L, 10 times the standard value, and restrictions were placed on the use of groundwater by nearby residents. 1997 saw the passage of the Soil Contamination Countermeasures Law by the government, which strictly controlled the disposal of liquid waste. Cleaning companies and metal processing plants were identified as the main sources of contamination.

### 2000s
**Expansion of pollution and strengthening of monitoring system**.
In the 2000s, groundwater contamination expanded nationwide, especially in Ichikawa City, Chiba Prefecture, where trichloroethylene discharged by Toyo Kagaku Kogyo reached a concentration of 0.35 mg/L, 10 times the standard value, and drinking water use was restricted throughout the region. In 2002, the Law for Promotion of Proper Management of Chemical Substances was enacted, further tightening regulations on the treatment of liquid waste by companies.

### 2010s
**Progress in remediation technology and new contamination discoveries**.
In the 2010s, purification technology made significant progress. In the Tama region of Tokyo and Kawasaki City, activated carbon adsorption filters and bioremediation technologies were introduced to purify groundwater. In particular, "Kawasaki Technology" proceeded with a 50 billion yen purification project that reduced the concentration of trichloroethylene to 0.02 mg/L, below the standard value.

### 2020s
**Strengthening of Monitoring System and New Challenges**.
In the 2020s, the monitoring system was strengthened mainly in Ichikawa City, Chiba Prefecture, Koshigaya City, Saitama Prefecture, and industrial areas in Tokyo, where groundwater contamination is monitored in real time. In some areas, trichloroethylene contamination, 15 times the standard value, was still found at Toyo Kagaku Kogyo, and companies are still lagging behind in their response.