The WWTP was upgraded in 2008 to remove phosphorus from the
discharge in a bid to reduce the growth of algae, bacteria and
microbes (periphyton) downstream thereby reducing the impact on the
macroinvertebrate community - mayflies.
Last year concerns were raised after river sampling found a
decline in the quality of the macroinvertebrate community
downstream of the discharge.
PNCC and HRC agreed on a joint monitoring programme and engaged
Opus International's principal environmental scientist Keith Hamil
to help investigate the concerns and it's his peer reviewed report
that is being publically released today.
The report has found periphyton grew three-times faster at a site
800m downstream of the WWTP discharge than upstream and that this
has a significant adverse effect on the macroinvertebrate community
during long dry periods.
Water and waste services manager Rob Green says work carried out
in 2008 to improve the discharge has not been as effective as
expected when the resource consent was granted.
Mr Green says, "the report has eliminated most of the causes of
the growth in periphyton and council staff acknowledge it is clear
nutrients emanating from the WWTP discharge are the likely
However, he says further investigations are required into river
sediments, ammonia levels and macronutrients to pinpoint the exact
"We are committed to working proactively with HRC to ensure
solutions are found. A work plan is currently being prepared and it
will be work-shopped with Councillors before being formally
reported back to Council."
The work plan is expected to include
changes - trial: increased alum dosing around long dry
investigation - of river sediments
monitoring - of periphyton levels and the macroinvertabrate
Both Councils have also agreed that a resource consent review
should occur and work is expected to begin on that shortly.
PNCC acting chief executive Ray Swadel says PNCC is committed to
improving the situation and ensuring the discharge meets the
consent conditions in the timeframe provided.
Next week Councillors will receive the joint report and staff
recommendations for consideration.
"At this stage it's too early to say how much the project will
cost," says Mr Swadel. "Initially it will be carried out from
within existing budgets however it is anticipated that at some
stage staff will need to go back to Councillors to seek further
funding to continue the project."