Monitoring of individual drain flows and quality will continue during the closure period. It is expected that individual drains will be piped to the Ohinemuri River and Ruahorehore Stream once monitoring indicates that the discharge will not have a significant adverse effect on the receiving waters.

Newmont Waihi Gold will provide sufficient funds to the post closure trust to allow it to carry out monitoring of the drains and the receiving waters in the long term. The Water Treatment Plant will be gifted to the Trust to allow water to be treated in the unlikely event that this becomes necessary. For further information see Closure and Post Closure.

A number of scenarios were looked at to determine what would happen if, for instance, the underdrains, upstream cutoff drains, initial toe drains and gully drains became blocked, and seepage was able to bypass the underdrainage system (bypassed seepage). A computer model was used to model seepage through the embankments and the underlying foundations. Modelling of the effects of seepage on both the Ohinemuri River and the Ruahorehore Stream was carried out. This took into account varying infiltration rates through the capping layer.

It was found that the upward movement of groundwater provides a significant constraint to seepage out of the embankments. In the event that bypassed seepage should occur in the long term, the modelling demonstrated that it would not have any significant adverse effects on the Ohinemuri River or Ruahorehore Stream.

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