Restoring the Health of Kawakawa Bay

Kawakawa Bay is a small coastal settlement on the south eastern coast line of the Auckland Region, 35kms east of the Manukau CBD. The Bay contains approximately 270 dwellings and has a population in the order of 600 predominantly permanent residents, although the population increases significantly during the summer period. Until 2012 wastewater treatment and disposal was by on site systems, mainly septic tank and soakage trench. 

Since 1997 and until recently, numerous water quality investigations in local streams and along the Kawakawa Bay foreshore indicated that the existing septic tank systems were causing contamination of stormwater, groundwater and in the Bay. 

In 2002, as public health concerns were increasing, the then Manukau City Council implemented short term health protection measures for the community, which included erecting signs in the area warning people of the risks associated with bathing and shell fish gathering and offering hepatitis inoculation to residents as well as regular pumping out of septic tanks. A moratorium on further residential development within the Bay was also put in place until the sewage disposal issue was resolved. 

In December 2004, Council called for design-build-operate (DBO) tenders for the implementation of a wastewater scheme. Following the evaluation of tenders Council awarded (2005) the DBO contract to Fulton Hogan whose designer for the project was Harrison Grierson. The contract period was extended by nearly 3 years largely due to issues relating to the granting of some resource consents for the project. The sewerage scheme was handed over to the client, Watercare Services Limited following the successful completion of the 3 month proving period followed by the 18 month operations period, in March 2013. 

The offer was based on a vacuum collection system and a 4 stage Bardenpho (nitrogen removal) wastewater treatment plant with the final aeration tank converted into a membrane bioreactor (MBR) that provides improved treatment efficiencies and disinfection of the treated effluent. 

This paper will describe the how the implementation of the sewerage scheme at Kawakawa Bay has conserved, improved and is now preserving the local environment and has removed the public health risk from the community that enjoys the intrinsic value of the coastal ecosystem.