Independent biological consultants sample in the mixing zone to ensure that marine life is not being adversely affected. Following a review of the substantial amount of data gathered from 1985 to 2003, which shows a continuous decline in metals, the ARC reduced the monitoring requirement to biannually from 2003.
The water quality standards set for the wastewater discharge to the Waiuku Estuary were derived following consideration of the potential for adverse effects on marine organisms and possible accumulation of metals in sediments within the mixing zone. Monitoring of metals in sediment and shellfish provides a sensitive indicator of the degree of contamination by metals in the marine ecosystem. The monitoring results for shellfish and sediments within the mixing zone are forwarded to the Auckland Council. The Council also conducts surveys in the Waiuku Estuary and wider Manukau Harbour.
