A $2.1 billion sewage plant which opened yesterday will only be able to function at a quarter of its capacity because of delays by contractors, according to government engineers. The treatment works, a key to stage one of the Strategic Sewage Disposal Scheme, are designed to treat 1.7 million cubic metres of waste a day from urban Kowloon and northeast Hong Kong. Chemically enhanced primary treatment will reduce by 70 per cent the amount of sewage pouring into Victoria Harbour. But Director of Drainage Services John Collier admitted he was disappointed with progress on the scheme, which was delayed after contractors downed tools last year, saying two of the tunnels were leaking dangerously. The Government would try to recover the cost of completing the project from the original contractors but was now considering bids from other companies. The first contract will be awarded in July but the Stonecutters Island plant will not reach full capacity until late in 2000, he said. Low flow through the plant means the interim outfall which runs 1.7 kilometres from Stonecutters into the Western Harbour approaches cannot be used and effluent will be discharged only 100 metres from the plant. A joint Hong Kong mainland environmental impact study is under way to determine the location of the controversial deep-sea outfall and the level of treatment - stage two of the Strategic Sewage Disposal Scheme. Secondary or biological treatment would be expensive but had not been ruled out, he said.