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.
A non-notified resource consent was sought which necessitated that environmental
effects be shown to be less than minor', and resulted from robust science and a
pragmatic approach to design. As part of the assessment of environmental
effects, there was a need to understand the effects of boron concentrations on
aquatic organisms (ie algae, plankton, plants and invertebrates) in the
receiving environment. Boron is a naturally occurring element that is found in
the form of borates in the oceans, sedimentary rocks, coal, shale, and in some
soils but Waikato coals and ashes have particularly high boron
content. Boron is an essential micronutrient for higher plants with interspecies
differences in the levels required for optimum growth. As aspects of the ANZECC
(2000) derived boron limits are based on toxicity of aquatic algae and plants to
boron it was important to assess these components in the environment. The
effects on the receiving environment of the Awaroa Stream were assessed using
predicted water chemistry and comparing actual boron concentrations in a
comprehensive and multifaceted reference-condition approach of catchment
ecological indicators. In addition a toxicological-based assessment of boron and
a re-calculation of the ANZECC trigger levels were undertaken and applied to the
ecological indicators. The reference-condition approach revealed that habitat
and overall water quality attributes at and between sites was more influential
in determining the aquatic biotic communities than boron concentrations alone.
There was no evidence of any gradient of changes in ecological indicators with
changing boron concentrations, nor evidence of any residual effect of high
historic boron concentrations on the aquatic biota.