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Heavy Rainfall Discharges - Introduction

The Moa Point Wastewater Treatment Plant occasionally discharges a mixture of fully and partially treated sewage through its ocean outfall pipe into Cook Strait - approximately 1.8 kilometres from shore.

This only happens during heavy rainfalls when sometimes the amount of sewage coming to the plant exceeds the capacity for the secondary stage of the treatment process.

Discharge Map (45Kb PDF)

Environmental Effects

In 2003, Wellington City Council commissioned the Cawthron Institute to investigate the potential environmental effects of these occasional mixed discharges. The study concluded that these discharges posed minimal risk to public health, shellfish gathering and recreational activities.

In general, Regional Public Health have the following recommendations:

Do not swim near urban areas for 48 hours after heavy rains, due to the potential health effects of contaminated urban stormwater.
Do not gather shellfish for consumption at any time from coastal locations near urban areas.

Resource Consent

On 20 September 2004, Wellington City Council received consent under the Resource Management Act for these occasional discharges.

Consent only applies when the quantity of wastewater arriving at the Moa Point Wastewater Treatment Plant exceeds 3,000 litres per second (the plant's capacity for the secondary stage of treatment).

The consent expires on 8 January 2008 when the overall resource consent for discharges from the ocean outfall pipe will expire. At that time all aspects of the ocean outfall pipe discharges will be reviewed and a new consent sought.

Reporting & Monitoring

Under the terms of the consent the Council must monitor and record the details of any mixed discharge from the Moa Point plant and make these available to the public.

In addition to making the information available online, the Council also posts notification signs - two at Lyall Bay and one at Tarakena Bay. These signs explain the location and nature of the discharge and the potential risk to public health from bathing or collecting shellfish in the vicinity. These signs remain in place for seven days after the discharge ends.

Coastal Water Quality Improvements

The Council spends over $20 million annually on improving water quality in the inner harbour and along the south coast. In the past few years the Council has:

extended the network which delivers sewage to Moa Point treatment plant
reduced sewage overflows
closed the sewage outfall near Owhiro Bay.

Future Plans

The Council is investigating options to further improve the city's sewerage system and dispose of sewage in an economical, environmentally friendly way. These options include:

increasing the treatment capacity of the Moa Point Treatment Plant
increasing storage within the sewerage system to reduce peak flows
doing more targeted inflow and infiltration studies.