In 2005, Solid Energy New Zealand Limited obtained
non-notified consent for the disposal of 1Mt of coal ash at the Rotowaro
minesite, forming part of a coal supply agreement with the Huntly Power Station.
The consenting of major mine site activities has historically required wide
consultation and involves notification of the application.

The risk and cost associated with consultation can be
significantly reduced via a non-notified process. A non-notified consenting
process necessitates environmental effects to be shown to be less than minor',
which requires the combination of robust science and a pragmatic approach to
design, assessment of environmental effects, and consenting
issues.

Key issues examined included consideration of how to
practically operate a significant disposal project within the confines of an
operating mine, minimising the costs, civil and geotechnical design and
practical issues associated with traditional disposal. Environmental issues
specifically related to the coal ash, led to a site specific performance driven
approach to management rather than relying on conventional prescriptive
approaches. Environmental issues of concern include the leaching of boron and
aluminium from ash into groundwater and mine water management systems where both
boron and aluminium can occur at elevated levels.

Coal ash exhibits unusual geochemical characteristics
reflecting the primary coal composition and the combustion process. The dominant
coal type combusted at the Huntly Power Station is derived from Rotowaro and the
resulting ash is cementitious and has a high alkalinity. As a result the
disposal design is based on the characteristics of the ash itself rather than
the material into, or onto which the ash is disposed. Non-notified status was
able to be achieved through consideration of these key characteristics of the
ash, ensuring that the dimensions of the disposal site and each location was
designed to minimise the flow of groundwater through the ash and demonstrating
that the physical ash disposal effects are less than minor compared to the
consented mining operation.