Cost-effective and Reliable Inflow-Infiltration Reduction – Have They Got It Right Down-Under?

Up until 2010, due to extreme drought conditions in much of Eastern Australia arising from a predominantly El Nino weather cycle in the Pacific Ocean over the preceding decade, Inflow and Infiltration(I/I) management practices in Australia had not progressed or been implemented to an great extent further from the initial implementation work done in this field, mainly in Sydney in the 1990s. However, over this same period, due mainly to very different climatic conditions, there has been a significant amount of work done throughout New Zealand in I/I management.With the onset of the wetter, predominantly La Nina patterns and the associated end of the drought in the 2008-2010 period, the management of wet weather flows in wastewater systems is now receiving more focus than at any time in the past 15 years in both Australia and New Zealand.The Water Services Association of Australia (WSAA) is an industry membership organization that represents the 25 largest water companies/authorities in Australia and New Zealand. To respond to the evolving market need of its member organizations, WSAA recently engaged GHD, in association with local consulting partner Urban Water Solutions (UWS) to develop a Best Practice Guideline Document on I/I Management.The initial part of this project aimed at determining the range of current I/I management practices in use across Australia. These practices and the resulting I/I reduction outcomes were compared and benchmarked with known and researched practices in New Zealand, USA and South East Asia.Using the practices implemented in the identified examples of successful project outcomes, a Good Practice I/I Management Guideline Document for Australian and New Zealand water utilities was developed. This document is has now become the industry guideline document for I/I management programs across Australia and New Zealand.Comparison with various practices in I/I reduction and management in the USA carried out in the study indicated a range of processes were being used in different jurisdictions in the USA and a broad range of outcomes were being achieved. Given the initial drivers for the WSAA project, this suggests that the findings of the WSAA work are potentially also very relevant in the USA and Canada. What the WSAA work found was that from the significant number of projects whose outcomes have now been analysed, there is now a robust knowledge base upon which to make far more reliable and informed predictive estimates of I/I reduction levels achieved from different levels of system rehabilitation. The work in New Zealand has evolved to a point where a predictive model of the likely level of I/I reduction that can be achieved from existing levels for different extents of system rehabilitation now exists.This is considered to represent a significant advancement worldwide in the planning of wastewater system improvement and management programmes.Of greatest value to the wastewater systems industry is that the work gives wastewater planners and managers a far more robust basis upon which to undertake I/I reduction programmes through system rehabilitation with the expectation of certain outcomes for a given financial investment.Some useful analysis and calculation tools to consistently support this methodology and also guidance on realistic targets and likely outcomes provide particular added value.Hence its contents can be used to more reliably plan works of this type and their associated capital budgets, reducing the risk of failure that has plagued such programs in the past. This outcome therefore removes many of the perceived risks associated with the implementation of I/I management programmes in the past.This paper will be of interest to the wide range of delegates challenged by the issue of infiltration and inflow in the effective management of their wastewater systems.