Discharges of Treated Wastewater to the Ruamahanga River

Stuff asked if the Council discharges of treated wastewater to the Ruamahanga River complied with its consent. The following information was provided:

In summer, the Council only discharges treated wastewater to the river when it is above median flow, which is 12.3 m3/sec. (In the winter, the limit is half this - 6.15 m3/sec).

We also have a requirement to ensure that the dilution rate is at least 30:1.

The river is currently running at 17.6 m3/sec, so we are able to discharge within the consent limits. We are however discharging at only 194 l/s, which is a 90:1 dilution.

Generally, we aim to only discharge when the river is running over 20 m3/sec, and at a dilution rate of at least 40:1, but this is not always possible

At present, are operating at the consent limits, due in part to the high rainfall events we have experienced in the last few weeks, which have increased the inflow into the treatment plant. We need to discharge to stay ahead of the flows and the flow rate of 194 l/s allows us to do this.

The discharge will reduce and then stop as the river level continues to drop. At that point, we will switch to purely land-based irrigation of the treated wastewater.