PART A The Hoppers Crossing Pumping Station is one of the principal components of the Western Trunk Sewer Project which replaces the 90 year old Main Outfall Sewer and will convey 60% of Melbourne's sewage flow from Brooklyn to the Board's Farm at Werribee. Part A of this paper deals with the geotechnical investigations carried out to confirm the pumping station location and acceptability together with subsequent ground investigations which enabled a geotechnical model of the site to be developed. This included soil and rock properties and type, a rock defect survey, ground water studies and the sinking of two adjacent shafts required for complementary tunnelling works. A number of methods were considered for assessing the design loads in both the clay and the rock zones of the pumpwells. The final ground support system adopted included rock dowels, rock bolts, shotcrete and mesh for the basalt and concrete encased steel ring beams for the basaltic clays. As the support system was based on a geotechnical model it was important to monitor ground movements to be able to ensure a safe and stable excavation. A monitoring system comprising extensometers, shear strips and face monitoring points was Installed.