Consenting Of The North East Sub- Regional Wastewater Scheme

Watercare currently operates two wastewater treatment plants (WWTPs) at Warkworth and Snells Beach, both of which required new consents to discharge. There were many factors to be considered in applying for new consents. This paper outlines some of the major drivers for the project and how they were addressed in developing the proposed scheme. These drivers include population growth, environmental constraints, short and long term effects, and the impact on the local community.

The existing plants service a combined equivalent population of approximately 10,000. The Auckland Unitary Plan forecasts significant growth in the area of consideration, particularly in and around Warkworth. Over the 35 year term of the consent sought, the population was projected to increase to a total of approximately 30,000 with 80% located in Warkworth. This represented a 6-fold increase in capacity requirement for Warkworth WWTP.

Warkworth WWTP currently discharges into the Mahurangi River. The Mahurangi estuary is classified as a degraded waterway. Within the estuary, there are oyster farms which could be affected by wastewater discharges if they are not of a very high quality. The existing wastewater treatment plant provides a high level of treatment, producing relatively low nutrient and bacteriological concentrations in its discharge. To maintain, or reduce the loads discharged, for the projected increased flows would be very difficult with existing technology. These factors combined give technical, environmental and social drivers for stopping the discharge of wastewater to the Mahurangi River.

Snells-Algies WWTP is an oxidation pond system which discharges to the coastal marine area via an ocean outfall. There is capacity at the plant to service the local population if the same discharge standards were retained. However, with pressure to improve the discharge quality upgrades would have been required for improved ammonia removal and disinfection.

A scheme was identified to transfer the wastewater from Warkworth to Snells Beach. A new wastewater treatment plant will be constructed at Snells Beach WWTP site producing a very high quality effluent. The existing ocean outfall will be replaced to enable a larger discharge flow for the combined scheme. Consents were applied for and granted, for the discharge to the coastal marine area, construction of the new outfall, land use at proposed pump station locations emergency discharges from the pump stations. This has paved the way for the implementation of the North East Sub-Regional Wastewater Scheme.