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.

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