Australian Water Management Review Vol. 1 2014 | Page 11

Wsaa
WasteWater
systeM
infloW and
infiltration
ManageMent
Steve carne, GHD Limited, auckland, New Zealand
Neil moody, urban water Solutions, melbourne, australia
Dr Jaimie Hicks, water Services association of australia

Introduction
With the recent La Nina weather cycles increasing
rainfall along most of eastern Australia and New
Zealand, the management of rainfall dependent
inflow and infiltration (I/I) as a means of reducing
wastewater overflows is now firmly back on the
agenda of wastewater system managers on both sides
of the Tasman. Responding to a clear need to fill
knowledge gaps in this area amongst its membership,
the Water Services Association of Australia (WSAA)
has commissioned the development of a Good
Practice Guideline document.
This project effectively represents the definitive
research work into I/I management practices. The
resulting Good Practice Guideline Document can
now be used by wastewater system managers
to more confidently implement I/I reduction
programs as a means of better managing
wastewater system overflows.
Methodology
Survey questionnaires were sent out to all
WSAA participant organisations to develop an
understanding of current and intended approaches
and practices related to I/I management. The
results of these surveys were used to provide an

understanding of the current practices in place
and to define the scope and required outputs for
the subsequent stages of the project works.
Research was conducted on best practice works
in Australia, New Zealand, the USA and Singapore
which indicated that while progress has been
limited in Australia in this area robust assessment
and management practices have continued to
evolve over this time in New Zealand and some
jurisdictions in the USA.
Features of the project’s output documentation
include the following –
• A comprehensive step by step guideline to
identify and quantify levels of I/I, guidance on
the likelihood of success of different mitigation
measures for different circumstances, direction
on the need for and approach for post
remediation analysis
• Definition and adoption of a consistent set of
I/I key performance indicators
• Discussion of the contentious issues
associated with the responsibilities for removal
of I/I entering the system through privatelyowned house laterals

• Detailed information on the quantification,
identification and removal of saline
groundwater reduction and seawater intrusion,
both of which impact on the useability of
treated effluent for irrigation
• Predictive guidelines and models for estimating
the levels of I/I reduction that can be achieved
for various levels of system rehabilitation.
• Advice regarding potential risks and failure
points in implementing a successful I/I
reduction programme.
Conclusion
The recently completed WSAA I/I Project
represents a significant piece of research of
wastewater system I/I management practices
throughout the world. It has produced a Good
Practice Guideline document which is now being
adopted by water agencies across Australia and
New Zealand.
It should be of significant value to wastewater
system managers around Australia and New
Zealand who are considering I/I reduction as
a potential successful and reliable means of
improved management of their wastewater system.

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