Pressure Sewer Applications in Commercial Developments

The application of pressure sewer technology has been increasingly used in Christchurch following the earthquakes of 2010/11. In general, these applications have been limited to residential applications, through the rebuild of damaged infrastructure in highly liquefaction prone areas or the replacement of septic tanks in small communities on Banks Peninsula. Pattle Delamore Partners (PDP) were engaged by a large commercial land developer to investigate options for servicing of approximately 40 Ha of industrially zoned land in south west Christchurch. The investigation incorporated developing concept designs for gravity reticulation and pressure sewer reticulation options. A significant challenge associate with pressure sewer was the requirement that the proposed network would be able to service the maximum permissible density of development under the City Plan zone rules. This was approximately 6 times the density of development envisaged by the developer at completion of the development. A flexible pressure sewer design concept was devised by PDP which would meet the require design parameters for both the minimum and maximum possible design density scenarios. This was achieve which still meeting the key criteria with respect to self-cleansing velocities and residence times in the reticulation network for moth the maximum and minimum development scenarios. The proposed concept was a “win-win” for both Christchurch City Council (CCC) and the developer. CCC would save considerable annual operation and maintenance costs associated with the operation of a conventional wastewater network for the development, while the developer saved approximately $1 million in capital construction costs.