A rigorous monitoring programme has been established by the water quality and the receiving environment and includes:
- Daily grab sampling
- Flow proportional composite sampling
- Biological monitoring in the mixing zone (the area where the discharged water mixes with estuary water)
- Continuous turbidity sampling
Daily Grab Samples
The quality of wastewater is controlled and monitored as it leaves the wastewater treatment plants. Each day New Zealand Steel laboratory staff take samples of the wastewater before the discharge enters the Waiuku Estuary. The onsite laboratory tests these samples and the results are reviewed to ensure that discharges continue to comply with resource consent conditions. The results are reported to the Auckland Council each month, and the Community Environmental Committee four monthly.
The composite sample is done on a 24 hour flow proportional basis. That means at the Northside Outfall, for every 100 tonnes of water discharged from the steel mill a sample of water is abstracted into the day's sample container. After 24 hours, these samples are taken to the laboratory for analysis. The results are electronically transmitted to operations and environmental staff who compare the results with the conditions set by the resource consent.
Discharge Water Quality Standards
On the northside and southside outfalls, the elements which are analysed in the laboratory and the frequency of sampling are listed below. These are specified in the resource consents held by New Zealand Steel.
• temperature • pH (acidity scale) • suspended solids • dissolved oxygen
• oils • iron • zinc • chrome • lead • nickel
In addition a continuous turbidity (clarity) meter operates on the separate ironsand dewatering plant discharge, where the only potential contaminants are clay minerals derived from the ironsand deposit.
Biological Monitoring in Mixing Zone
Where the wastewater discharges into the Waiuku Estuary there is an area in which the wastewater mixes with the water of the Estuary. This is referred to as the New Zealand Steel 'mixing zone'. 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.
Monitoring Air Quality in the Community
New Zealand Steel has an air monitoring programme in place to assess air quality at the boundary of the industrial site and in the community. Continuous monitoring of the effect of Glenbrook's operations is an essential part of the company's commitment to minimise emissions. Special studies have also been commissioned by the company to consider the effect of emissions on the community and agricultural activity in the surrounding area.
The regular monitoring programme includes:
- Measuring total suspended particles in the air, at six sites in the community
- Measuring particle matter and chemicals in stack emissions
The objectives of the monitoring programme are to:
- Observe trends and patterns in ambient air quality over time
- Make sure that the company complies with its consent conditions
- Obtain data about background levels of air pollutants
- Confirm that air pollution control equipment is cleaning air emissions effectively
Air quality monitoring equipment is stationed around the outskirts of the mill to measure the quantity of dust particles in the air. Samples are collected weekly for evaluation by the company's environmental staff and are compared with nationally accepted standards. The air emissions discharged via stacks are also monitored regularly. Sampling equipment is inserted inside the stack and a sample is taken to measure the volume of dust emitted from the stack, or hydrogen chloride levels in the case of the pickling line, where acid is used in the process.