Introduction

Recently, an Aluminium Smelter underwent expansion adding a new potline to the existing operational potlines. The expansion was designed to massively increase the production capacity of the plant. To accommodate this increase in production capability, other sections of the plant had to be modified and/or expanded.

A principle environmental noise requirement of the project was that the new potline and expanded facilities were not to cause an increase in the existing background noise level in the surrounding community, and that the new development was not to hinder the ongoing noise reduction programme of the existing potlines and associated facilities. A second requirement was that within the new potline and upgraded facilities, the internal noise levels were not to exceed the proposed Occupational Health and Safety noise limits of 85dB(A) when in full production.

Project Management

The acoustic brief covered all phases of project/acoustic interactions.

The construction company was supplied with extensive engineering advice on the building constructions, machinery designs, machinery layouts, and machinery selections. The acoustic requirements were most economically incorporated into their designs and specifications.

Seperate acoustic specifications were prepared and issued to equipment suppliers, detailing information requirements and noise limits. The details included information format and measurement procedures to be used by suppliers in providing the necessary information. Where an equipment supplier was unable to supply specification details, the supplier's own noise information was used to modify the overall design to accommodate these variations. As designs and constructions progressed, ongoing changes were introduced to accommodate variations which occurred within large projects. Each sub-contractor was required to submit noise guarantees. Following installation of equipment, the contractors had to provide certification confirming that they had achieved the guaranteed noise limits in accordance with the standard test procedures set down in the specifications. All this information had to be submitted for verification by the accredited acoustic engineers.

Environmental Noise Monitoring

At the same time, the smelter environmental group commissioned "before and after" computerised noise emission simulations of the Smelter, and an assessment of the likely noise intrusions into the surrounding residential areas.

All equipment and buildings on the site were measured and the determined sound power levels were entered into a computerised acoustic model of the site and surrounding areas. This exercise was repeated and included the proposed new expansion which at that stage had not been constructed.

Typical noise values obtained from the existing plant and from construction information was used to model the expansion. This exercise permitted the smelter noise contributions to be extracted from the existing background levels as part of the smelter operator's ongoing commitment of complying with the requirements of the Environment Protection Authority.

In conjunction with the computerised modelling, an extensive automated field noise monitoring program was undertaken over a large area and continued over an extended period of time. Following the processing of the automated noise monitoring results to remove extraneous noise data, the computerised acoustic simulations were found to be accurate to within ±1dB(A) at all residential locations monitored.

The computerised acoustic model permitted the clear identification of both meteorological conditions and noise sources responsible for the noise levels measured in the local community. The computerised acoustic model provided a full ranking of noise sources within the site by component contribution to each monitoring location.

This approach has proven to be a valued tool in the smelter operator's long term strategic planning for noise reduction to meet the legal requirement of Environment Protection Authority.

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