On-site wastewater management system design and performance is significant in assessing landslide risk in areas with potential for slope instability. Much of the development in Pittwater, NSW, local government area is on steep coastal land which has a history of slope instability. Concern over cases of poorly performing or failing on-site wastewater systems and the recognition that these and newly designed systems could be contributory to slope instability has been a factor in Pittwater Council, NSW, requiring that landslide risk assessment be undertaken for new and amended on-site wastewater management systems in potentially unstable areas.

This paper describes the wastewater management system design and landslide risk assessment undertaken at Pittwater Youth Hostel in accordance with the Australian Geomechanics Society's Geotechnical Risk Management procedure to comply with the Pittwater Policy. The work completed illustrates both necessary and effective interaction of the wastewater and geotechnical professions to achieve a successful outcome for the client. It is likely that this professional interaction will be increasingly common along the NSW coast and elsewhere.

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