The Environment of Tokyo 2008

• Foreword
• The Master Plan Layout
• The Revised Ordinance
• An Olympic Games with Its Top Priority on The Environment
• Two 10-Year Projects

◎ Rivers in Tokyo are Becoming Cleaner

There are about 120 rivers flowing through Tokyo, including the Tama River, the Edo River, and many smaller ones. Although the water quality of these rivers significantly deteriorated during the period of high economic growth, there has been a remarkable improvement since the early1970s, thanks to the control of sources such as factories, and improvements to the sewage system. Since then, river water quality has improved or remained unchanged.

According to a study conducted in fiscal 2006, the percentage of water areas meeting the Biological Oxygen Demand (BOD^*1) requirement, an index of environmental quality indicating pollution levels, was as high as 96%.

◎ Condition of Seawater —“Red Tide” An Algal Bloom in Tokyo Bay—

Compared with the early 1970s, the water quality of Tokyo Bay has significantly improved. However, it suffers chronically from the condition of eutrophication, leading to algae bloom, mainly on hot summer days, which affects the water quality of the bay.

As for the water quality of inner Tokyo Bay,^*2 the value of Chemical Oxygen Demand (COD^*3) improved steadily to 1980 and leveled off thereafter.

Tokyo Metropolitan Government (TMG) is taking various actions to prevent water pollution of rivers and Tokyo Bay including sewage improvement in addition to regulating and giving guidance on factories and sewage plants.

◎ Wastewater Regulations for Factories and Business Facilities

TMG regulates the concentration of poisonous substances such as cyanide and mercury in wastewater, while controlls the total amount of COD, nitrogen, and phosphorus based on relevant laws and the Tokyo Metropolitan Environmental Security Ordinance. TMG sets stricter standards by the Ordinance than national standards to regulate water quality, and gives guidance on improving wastewater quality based on these standards. Factories and business facilities located in the drainage basin flowing into Tokyo Bay discharging more than 50m³ of wastewater per day are required to comply with the standards for the total pollutant load control assigned for each factory or establishment.

These efforts have contributed to a steady improvement in water quality, returning fish and aquatic life to rivers and the sea.

Continuing urbanization has increased the ground coverage rate while more rainwater is flowing into sewers and rivers. This hampers the creation of a healthy water cycle and causes deterioration of the waterfront environment. Tokyo Metropolitan Government (TMG) has taken various measures to restore a healthy water cycle by utilizing leaked groundwater and conserving natural springs, and also by promoting groundwater conservation.

◎ Waterfront Environment

To preserve about 700 natural springs in Tokyo, TMG has formulated the Tokyo Metropolitan Guidelines for Natural Spring Conservation and Recovery in fiscal 2002 to conserve and recover natural springs in collaboration with municipal governments.

In fiscal 2002, TMG designated 57 natural springs as “Tokyo Superb Natural Springs” at the recommendation of the residents of Tokyo and local municipalities.

Also, advanced sewage treatment water and leaked groundwater is channeled to urban rivers with particularly low water levels to aid recovery of the waterfront environment.

◎ Recovering Clean Streams

The Nobidome waterway, the Tamagawa channel, and the Senkawa channel that had been left dry were restored in 1984, 1986, and 1989, respectively, by channeling advanced sewage treatment water from the Tamagawa Joryu Water Reclamation Center. Clean water has been maintained in these waterways ever since.

In addition, Shibuya River, Furukawa River, Meguro River, and Nomi River have been channeled advanced sewage treatment water from the Ochiai Water Reclamation Center since 1995.

◎ Ground Subsidence Abated

In Tokyo, the ground has significantly subsided due to excessive drawing off of groundwater, mainly in lowlands, since the early Taisho period. In some areas cumulative subsidence has reached 4.5 meters. To date, ground subsidence has caused various types of damage, such as the distortion of buildings and the deformation and breakage of underground piping, leading to a requirement for measures to prevent damage by flooding and high tides.

TMG has now controlled the drawing off of groundwater through applicable laws and the Tokyo Metropolitan Environmental Security Ordinance, and as a result, further ground subsidence has now abated. However, subtle subsidence still continues in many areas.

◎ Groundwater Recharge

Groundwater levels in Tokyo are rising in lowlands in the ward area, while they are unchanged or rising very slightly in other areas. Accordingly, in addition to restrictions on drawing off groundwater under the Tokyo Metropolitan Environmental Security Ordinance and others, TMG formulated its Rainwater Infiltrating Guide in July 2001 and is promoting installation of rainwater infiltration facilities to recharge and conserve the groundwater.

◎ Increase of Hot Springs

In recent years, there has been an increasing amount of hot spring drilling in Tokyo mainly at depths exceeding 500 meters. TMG imposes restrictions on the amount of pumping and the distance between hot springs in accordance with the Hot Spring Law and criteria independently determined by TMG in an effort to prevent ground subsidence and the depletion of hot spring resources caused by the increase in the pumping of hot spring water.

Furthermore, in view of the accidental explosion at a hot spring facility, TMG developed guidelines on safety measures for works from drilling to abolishing hot springs to ensure safety.