BOTCHED maintenance work together with a leaking sewage pipe are the possible causes of the fatal Kwun Lung Lau landslip two weeks ago, according to a preliminary government report published yesterday. The initial investigation by the Geotechnical Engineering Office (GEO) shows that the rainwater drainage system had been improperly connected to the underground sewage pipe at some time since the estate was built in 1965. This increased the amount of water flowing through the drainage network and the amount draining away through leaks in the pipe. Plans of the sewer network show that 300 millimetre diameter pipes ran between a series of manholes. One of these manholes was in the slope that collapsed. Some of the earth around the pipes and manholes had turned black where water had leaked out. ''We have checked the sewer connections when the estate was built in 1965 and it is exactly as it was supposed to be on the original plan. So we believe the surface drainage connection was made some time after, but we do not know how, when or who did it or even if it was approved under the Buildings Ordinance,'' said acting Principal Government Geotechnical Engineer John Massey. He said checks so far with Drainage Services and other government departments had not yet uncovered any information about how the two systems became linked. This increased the chances contractors had wrongly connected the two networks. Engineering experts would not normally have checked whether the two systems were linked. A proper check could have been done only when it was raining, when an analysis of the waste water would have revealed a higher concentration of clear water, or by using a special dye. ''We cannot understand why the sewage pipe was carrying storm water,'' said the Acting Director of Civil Engineering, Dr Andrew Malone. He said a detailed assessment of the landslip revealed that water had penetrated the soil behind the slope and retaining wall. And although the most likely cause of this was the leaking or broken sewage pipe, Dr Malone said it could have also been because the cement screen on the slope was cracked and broken or from naturally occurring underground water. Copies of the report have already been sent to the Housing Society, legislators and district board members. A copy has also gone to Professor Norbert Morgenstern, the independent expert who was appointed a week ago to carry out his own investigation into the landslip, which killed five people. The report also makes clear that the Housing Society's consultant, Mott Connell, recommended eight maintenance measures in a study of the retaining wall and slope done on June 15. The Housing Society was just about to invite construction tenders for the work when the tragedy happened. Asked if the consultants' recommendation exonerated the firm from any blame, the Secretary for Works, James Blake, said it was too early to tell. The GEO is urgently checking its records to see if there are other retaining walls and slopes in Hong Kong with the same features as those at Kwun Lung Lau Estate. It is likely to be several months before the final report on the accident is ready. Meanwhile, legislators yesterday called for the immediate release of the June report. They were amazed that nothing had been done to prevent the disaster. United Democrat legislator Albert Chan Wai-yip said he was ''shocked''. ''Why were no immediate measures taken when weak material was discovered?'' he asked. ''Is it the fault of the consultants or the Housing Society?'' He urged the Government to set up an independent judicial inquiry to look into the issue. He will seek to set up a select committee to launch an independent inquiry at the Legislative Council lands and works panel meeting next week.