ENG-2007 — Page 341

The Environment 285

granite. Igneous activity ceased 60 million years ago. Layered rocks now seen on Ping Chau Island are younger sediments, which settled in a lake on the edge of a desert.

During the last two million years, the Quaternary Period, several major glaciations affected the polar regions. These caused successive lowering of world sea levels of up to 120 metres, which resulted in present day Hong Kong being as far as 130 kilometres from the coast. During the interglacial periods, such as the present time, global sea level returned to its present position and marine sediments were deposited.

The geology of Hong Kong is depicted in a series of fifteen 1:20 000-scale geological maps and six accompanying geological memoirs that were produced by the Hong Kong Geological Survey unit, a part of the Geotechnical Engineering Office of the Civil Engineering and Development Department. The Hong Kong Geological Survey unit has also published two summary memoirs and a set of 1:100 000-scale geological and thematic maps that synthesise current interpretations of the geology of Hong Kong.

Energy

Gas

Towngas and liquefied petroleum gas (LPG) are the main types of fuel gas used in Hong Kong for domestic, commercial and industrial purposes. LPG is also used as a fuel by some taxis and light buses while natural gas is used for electricity generation and production of towngas.

Hong Kong has about 2.3 million gas customers in the domestic, commercial and industrial sectors. In 2007, Towngas accounted for 82 per cent of total fuel gas sold, while LPG accounted for the remaining 18 per cent.

Towngas is manufactured at plants in Tai Po and Ma Tau Kok, the former using natural gas and naphtha as dual feedstock and the latter using naphtha as feedstock. They have output capacities of 9.66 and 2.6 million cubic metres per day, respectively. Towngas is supplied through an integrated distribution system to about 1.6 million customers. The mains network extends throughout Hong Kong via a 140-kilometre high-pressure pipeline and some 3 100 kilometres of distribution mains.

LPG is imported into Hong Kong by sea and stored at five terminals on Tsing Yi Island before being distributed to approximately 690 000 customers and 58 LPG filling stations.

Natural gas is imported from the Yacheng 13-1 gas field off Hainan Island in southern China via a 780-kilometre submarine pipeline to the Black Point and Castle Peak Power Stations for electricity generation. The liquefied natural gas (LNG) terminal in Shenzhen supplies natural gas through a 93-kilometre submarine pipeline to Lamma Power Station for electricity generation. The LNG terminal also supplies natural gas through a 34-kilometre twin submarine pipeline to Tai Po plant for production of towngas.