The Environment Protection Authority issued a report 31 January 2013 on the Infrasound levels near windfarms and in other environments. The report is another nail in the coffin of anti-wind propaganda down under.
Below is a summary of the report’s findings. See the report for details on the acoustic study they undertook and the techniques they used.
Urban environments
The following findings have been drawn from the measurements conducted in the locations in urban areas:
- Infrasound levels of between 60 and 70dB(G) commonly occur in the urban environment.
- Infrasound levels were typically 5 to 10dB(G) higher during the day than at night time.
- Noise generated by people and associated activities within a space was one of the most significant contributors to measured infrasound levels, with measured infrasound levels typically 10 to 15dB(G) higher when a space was occupied. Infrasound levels up to approximately 70dB(G) were measured in occupied spaces.
- Traffic may also influence the infrasound level in an urban environment, with measured levels during the daytime periods typically 10dB(G) higher than between midnight and 6 am, when traffic would be expected to be at its lowest.
- At two locations, the EPA offices and an office with a low frequency noise complaint, building air conditioning systems were identified as significant sources of infrasound. These locations exhibited some of the highest levels of infrasound measured during the study.
Rural environments
The measurements conducted within rural environments included simultaneous measurements of outdoor and indoor infrasound. It was found that the outdoor infrasound levels were similar to or marginally above the indoor infrasound level.
The following findings have been drawn from the measurements conducted in the locations in rural areas:
- Infrasound levels at houses adjacent to wind farms (Locations 8 and 9) are no higher than those at houses located a considerable distance from wind farms (Locations 10 and 11). For example, the outdoor infrasound levels at Location 8 are significantly lower than those at Location 11, despite the house being located much closer to operational wind turbines (1.5 kilometres compared to 30 kilometres).
- Infrasound levels in the rural environment appear to be controlled by localised wind conditions. During low wind periods, levels as low as 40dB(G) were measured at locations both near to and away from wind turbines. At higher wind speeds, infrasound levels of 50 to 70dB(G) were common at both wind farm and non-wind farm sites.
- Organised shutdowns of the wind farms adjacent to Location 8 and Location 9 indicate that there did not appear to be any noticeable contribution from the wind farm to the G-weighted infrasound level measured at either house. This suggests that wind turbines are not a significant source of infrasound at houses located approximately 1.5 kilometres away from wind farm sites.
From an overall perspective, measured G-weighted infrasound levels at rural locations both near to and away from wind farms were no higher than infrasound levels measured at the urban locations. Furthermore, both outdoor and indoor infrasound levels were typically below the perception threshold by a significant margin. The most apparent difference between the urban and rural locations was that human activity and traffic appeared to be the primary source of infrasound in urban locations, while localised wind conditions are the primary source of infrasound in rural locations.
An additional analysis of the frequency content of the measured infrasound levels was conducted for each location. At both of the wind farm sites, peaks in the frequency spectrum corresponding to the turbine blade pass frequency and related harmonics (0.8Hz, 1.6Hz and 2.5Hz) were identified that may be attributable to the wind turbines. However, these peaks were only detectable during periods of low wind speed and therefore ambient infrasound at the residences. The peaks in the spectrum were found to be no higher than infrasound levels measured at these frequencies at both rural and urban locations away from wind farms, and also significantly (at least 50dB) lower than the threshold of perception for these very low frequencies.
Summary of results
The range of measured Leq,10min infrasound levels at each of the measurement locations is presented in Figure 1 on the following page, with the lines corresponding to the minimum, 25th percentile, median, 75th percentile and maximum infrasound levels from left to right.
It is clear from the results that the infrasound levels measured at the two residential locations near wind farms (Location 8 near the Bluff Wind Farm and Location 9 near Clements Gap Wind Farm) are within the range of infrasound levels measured at comparable locations away from wind farms. Of particular note, the results at one of the houses near a wind farm (Location 8) are the lowest infrasound levels measured at any of the 11 locations included in this study.
This study concludes that the level of infrasound at houses near the wind turbines assessed is no greater than that experienced in other urban and rural environments, and that the contribution of wind turbines to the measured infrasound levels is insignificant in comparison with the background level of infrasound in the environment.
