Western Australia Chapter

Wastewater Treatment Plant at Christmas Island

Stuart Masterson

The population of Christmas Island has trebled in recent years following the arrival of asylum seekers arriving in boats from Indonesia. Designing a WWTP for a largely itinerant population has presented a serious challenge to Water Corporation engineers. The project comprises upgrade of the existing WWTP at Smith Point, a new pumping station at North West Point, and a new pipeline from NW Point to Smith Point.

The geotechnical design issues included:

  • the presence of deep vertical fissures in karstic limestone formation;
  • rearrangement of the plant layout due to a large blowhole fissure at the clarifier tank;
  • cutting into the vertical limestone cliff to accommodate the sludge drying beds;
  • foundation design to span a narrow fissure intersecting with clarifier tank no. 2;
  • discharge of the treated wastewater into a narrow fissure within the site; – rockfall risk assessment for WWTP and pipe rack;
  • pump station and overflow storage tanks founded on fill and pinnacle limestone; and
  • surface drainage for pump station facilities into a local doling.

The talk will cover the geotechnical investigation techniques used by the Water Corporation and others as well as presenting photographs of the geotechnical features.

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.