Lessons Learnt From Retrofitting Existing Wastewater Catchments With Vacuum Sewer Systems Post-Earthquake

During the infrastructure rebuild after the Christchurch earthquakes in 2010 and 2011 as part of the Stronger Christchurch Infrastructure Rebuild Team (SCIRT) alternative wastewater systems were considered as a resilient alternative to replace the existing gravity systems in areas that were badly damaged by the earthquake.

During the concept stage of design, Vacuum Sewer Systems (VSS) were considered along with Pressure Sewer Systems as a resilient alternative to conventional gravity systems to replace the badly damaged existing gravity systems. Two existing gravity wastewater catchments in Shirley and Aranui servicing approximately 700 properties and 3000 properties respectively, were recommended to be replaced with a VSS due to their lowest whole of life cost, which included an indicative cost for the expected resilience of the systems against expected future earthquakes.

Pre-Christchurch earthquake there was limited industry knowledge of VSS in New Zealand, with only one VSS existing in Kawakawa Bay, south of Auckland, and no known international experience of retrofitting an existing gravity system that has been badly damaged by an earthquake with a VSS. As such, many lessons have been learnt during the design, construction, commissioning and operation stages that can be applied to future projects where considering utilising VSS. This paper looks at the lessons learnt during these stages.