Draft National Wind Farm Development Guidelines - July 2010

Undertake unattended monitoring to assess compliance with noise level limits
• Approach to sound indices
Establishing noise level limits requires review of measured LA90,T noise levels, a process
which may be repeated during the post-construction noise monitoring phase to
demonstrate actual compliance with noise level limits. Concurrently, noise emission
predictions are carried out typically using sound power level data described in terms
of LAeq. This may have caused some confusion in previous noise impact assessments.
These Guidelines recommend an approach as follows.
The direct measurement of LAeq from the wind farm, which is outlined in
Methodology 2 in Section 7.4 of AS4959–2010, may be a difficult and time
consuming process due to the varied amount of extraneous noise. For this reason
the method discussed below in Monitoring at the background noise level
monitoring location, which is comparable to Methodology 1 in Section 7.3 of
AS4959–2010, is intended to be a simple method and is likely to be conservative.
A minimum of 1.5dB needs to be added to the LA90 noise levels to obtain the LAeq
noise levels.
• Monitoring at the background noise level monitoring location
Unattended monitoring should be carried out as detailed in Section 7.3 of AS4959–
2010. While the Standard does not consider this monitoring to be required in every
circumstance it is the recommendation of these Guidelines that, in most cases,
unattended monitoring should be carried out for a sufficient period to demonstrate
compliance with noise level limits across a range of weather conditions which, in the
least, includes the worst case conditions where the margin between wind farm noise
emission and noise level limits is at a minimum.
If not specified, for example, in planning permit conditions, the proposed length of
post-construction noise monitoring should be agreed with the relevant authority prior
to commencement of monitoring. Indicatively, at least several months of monitoring
may be required to clearly demonstrate compliance with noise level limits. The costs
of monitoring should be borne by the operator.
Monitoring data should be used for analysis and assessment according to Sections
7.3.4 and 7.3.5 of AS4959–2010.
Where compliance with the noise level limits is demonstrated through the proposed
monitoring period without significant issue, further unattended monitoring is unlikely to
be required.
With unattended measurements it is generally only ever possible to demonstrate
compliance with assessment criteria. In the case that measurements suggest noncompliance
there will be doubt as to whether the measured levels are dominated by
wind farm noise emission or some other source.
One particular scenario when this is likely is where the background noise environment
at the monitoring location, in the absence of wind farm noise emission, has become
louder. This may be a result of new trees having been planted around the monitoring
location, or an increase in foliage on trees relative to when the original background
noise monitoring was carried out.
Where results of unattended monitoring are unclear and it is suspected that the
background noise environment at the monitoring location, in the absence of wind
farm noise emission, may have become louder unattended monitoring at a
secondary location is recommended, as discussed below.
In other cases where results of unattended monitoring are unclear, particularly if they
indicate non-compliance with noise level limits, attended monitoring will be required,
Draft National Wind Farm Development Guidelines – 2 July 2010 Page 57