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China challenge

As water is impounded behind China's Three Gorges Dam, a massive $500M wastewater interception and treatment project is under way at upstream Chongqing.

Chongqing municipality is home to more than 30M people. Development in recent years has been rapid, especially so since 2000 when the Chinese government introduced its Western Development Strategy which dramatically increased investment towards China's western provinces.

But infrastructure development has fallen far behind the burgeoning growth in industrial and commercial sectors. Less than 8% of industrial and domestic wastewater is currently collected and treated before being discharged to either the Yangtze or Jialing rivers which meet in the heart of Chongqing City.

Around 600 outfalls - many highly visible - currently discharge untreated effluent into the rivers.

Also requiring attention is the impending river level rise following closure of the Three Gorges Dam. In the two weeks from 1 June, the water level at the dam site had risen by 75m, just the first of three level rises that will affect even Chongqing, 650km upstream of the dam site. Since this will reduce water velocity and alter flow regimes, the river water quality will need to be maintained at an environmentally sustainable standard.

One of the new dam's key functions is to allow all-year access to Chongqing's harbour for 10,000t freighters, bringing economic benefits to the city. Although raising the minimum dry season river levels at Chongqing City, the dam will not significantly affect the maximum wet season levels in the city.

These and other environmental issues in Chongqing's urban centres are the focus of the ambitious Chongqing Urban Environment Project which involves wastewater collection and treatment, water supply and solid waste collection and disposal.

Of the total $500M cost - being funded with the help of a $200M World Bank loan - $300M is needed for new wastewater infrastructure, the project's largest single component. This involves the construction of 70km of primary interceptor sewers, including box culverts and more than 30km of drill and blast tunnel, plus two wastewater treatment plants with a total initial capacity of 0.9M. m 3/day discharging via two wastewater outfalls. A transfer pumping station of 16m 3/s capacity will be built, while an inverted siphon requires construction of a 5.4m diameter tunnel under the Yangtze River.

As many as 60 contracts make up the wastewater component which is being engineered and managed for client Chongqing Municipal Drainage Company by a team from UK consultant Mott MacDonald and French firm Sogreah, both involved since 1996 in masterplanning, feasibility studies and preliminary and detailed design phases.

Since Chongqing has virtually no wastewater collection system, extensive construction is having to take place in the main urban areas. 'This brings a host of challenges ranging from land issues to all the logistics problems of carrying out such major construction adjacent to existing buildings and structures, ' says Chris Preston, Mott MacDonald's project manager in Chongqing. 'At the same time we've got to ensure we meet the tight contract programmes and achieve the required levels of construction quality.'

Adding to the complexity is that Chongqing's development continues apace, with other infrastructure being built on the same sites. Several major roads are under construction along the banks of both the Yangtze and Jialing rivers where interceptor sewers are being built, for example.

'This means co-ordinating closely with the contractors for all these other projects as well as managing the interfaces on the dozens of our own contract packages, ' says Preston. Mott/ Sogreah are having to manage the numerous design changes needed to accommodate them, he adds.

'There have been plenty of surprises too, ' Preston says.

One was discovery of underground shelters dating back to the Second World War, which interrupted tunnelling for a major sewer on the Yangtze's north bank.

Construction of the wastewater elements is now well advanced and several of the initial batch of interceptors are nearing completion. Tenders have been invited for the civil works and equipment supply contracts for the two large wastewater treatment plants, Jiguanshi and Tangjiatuo, with construction due to commence later this year.

Around the same time site work is due to get under way on the major pumping station at Taipingmen and the 5.4m diameter inverted siphon tunnel running 925m beneath the Yangtze.

Chongqing municipal government has set an ambitious target of the end of 2004 for completion of all the works for the wastewater component, which will deliver wastewater collection and preliminary treatment.

A parallel project to provide primary and secondary treatment, funded by the Japan Bank for International Co-operation to the tune of $98M, is due for commissioning at the same time.

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