Principia Scientific International — February 12, 2014
Comments on the SA EPA Waterloo Wind Farm
Environmental Noise Study 2013
The following document is an analysis of the recent “Waterloo Wind Farm Environmental Noise Study” conducted by the South Australian Environmental Protection Agency (SA EPA). Overall, the report is well- written and reflects awareness of current international guidelines on low frequency noise and infrasound.
The use of specialised low frequency microphones and multi-layered windshields (in some cases) indicates that attempts have been made to ensure that the infrasound and low frequency noise is measured as accurately as possible. The inclusion of local weather station data, indoor measurement data and noise diary entries shows that there has also been an attempt to surpass the baseline requirements of the EPA guidelines. Finally, the large amount of information in the report has been succinctly summarised in tables and figures.
On the other hand, the EPA found “no evidence linking the noise from the wind farm to adverse impacts on residents” and there are several reasons why this conclusion may have been reached erroneously. These include certain limitations of the current guidelines as well as aspects of the study that could have been improved. In some cases, interpretation of the data has led to generalisations that are not well backed up by the supporting figures.
It is clear that the study undertaken by the EPA was comprehensive and complex. There are many ways of analysing and interpreting the data and the comments below are intended only to indicate the areas where I believe the analysis and interpretation could be improved.
The intention of my comments is to offer alternative interpretations of the data that I believe are valid and that do not result in the same conclusion of “no significant noise impact” that was reached by the EPA.
1. General Comments
1.1. Noise criteria
While there is significant discussion in the EPA report of the low frequency indoor limit proposed by the Danish guidelines as well as the third-octave indoor limit recommended by DEFRA, compliance is nevertheless determined based on the 40 dB(A) outdoor limit specified in the EPA guidelines (2009). It is not clear whether the EPA has used LAeq values or LA90 to determine compliance as this has not been explicitly stated. Wind farm noise can be significantly underestimated using LA90 levels due to the unsteady nature of the noise. The peaks that are associated with unsteady effects such as amplitude modulation are not present for 90% of the time and hence their disturbance potential is never evaluated.
Compliance is determined based on a regression analysis that effectively “averages” the range of noise levels for a given wind speed. This means that a considerable number of 10-minute-average data points may lay above the regression line of best fit even though the wind farm is still considered to be compliant. This is particularly problematic if those instances occur at night time during stable atmospheric conditions when the contrast between wind farm noise and ambient noise is greatest (Van den Berg, 2004). At night time, annoyance and sleep disturbance effects are also likely to be most critical. The reliability of the regression analysis could be improved by separating the results into daytime and night time and plotting separate regression curves.
A further limitation in the guidelines can be seen by comparing Figure 18 (a) and (b) for the “North East” residence. Plotting the measured sound pressure level (SPL) against wind speed at hub height shows compliance (Figure 18 (b)) whereas plotting against local wind speed shows non-compliance (Figure 18 (a)). However, it is often the case that the wind behaviour at hub height and in the vicinity of the residence bear no relation to one another, therefore Figure 18(a) appears to be the better choice for determining compliance. This argument is further supported by the better curve fit which has been attained in Figure 18 (a) compared to Figure 18 (b).
It should be noted that the SA EPA guidelines contain many references to work that was carried out in the late 1990s and the most recent reference was published in 2004. Hence, it is reasonable that these guidelines could be reviewed to take into consideration research work done since then and current international best practice guidelines.
There were a total of 6 shutdowns during the measurement period. All shutdowns occurred during the day with the exception of one from 5:10 am to 6 am. For the purpose of evaluating the impact of the wind farm on the community, I believe that it would have been more appropriate for the shutdowns to have occurred between the hours of 12 am and 5 am. During the night, people are trying to sleep and this time also represents the greatest contrast between ambient noise and wind turbine noise, due to the absence of other sources such as traffic and farming machinery. This would give more confidence that any excess noise above the background noise would be due to the wind farm. Moreover, it was mentioned that many files that were obtained during shutdown had to be discarded due to indoor noise sources not associated with the wind farm. For example, at the “North East” and “South East” residences, 4 out of 6 files could not be relied upon due to indoor interferences. Between the hours of 12 am and 5 am, it would be expected that indoor noise would be at a minimum since most people are sleeping during this time. Read full article here….