Pacific Hydro releases Cape Bridgewater Wind Farm acoustic study
21 January 2015
Pacific Hydro has today released the report ‘The Results of an acoustic testing program – Cape Bridgewater Wind Farm’, following a noise monitoring study conducted by The Acoustic Group at the Cape Bridgewater Wind Farm near Portland, Victoria.
While the Cape Bridgewater Wind Farm is compliant according to the noise standard adopted by the Victorian Government for the assessment and measurement of sound from wind turbine generators (New Zealand Standard 6808), Pacific Hydro decided to go beyond its compliance obligations in an attempt to better understand a number of concerns raised by nearby residents.
An important part of the study was the participation of six residents who agreed to keep observation diaries in which they were asked to record their awareness levels of noise, vibration and a new concept of ‘sensation’.
The report points to some preliminary findings which do not fall under the New Zealand Standard and go beyond guidelines set by the World Health Organisation. The findings are based on the acoustic study of low and infrasound frequencies using a narrow band analysis (of frequencies). It is generally accepted that the level of infrasound in proximity to wind farms is unable to be heard by the human ear.
The study featured an on-off testing component that showed there is a pattern of infrasound frequencies at the Cape Bridgewater Wind Farm when it is operating, and also at the three residences involved in the study. The report also states that there is a trend between the existence of these infrasound frequencies and the higher severity levels of ‘sensation’ as recorded by the residents in their observation diaries. It should be noted that the study found no correlation for noise or vibration with respect to the operation of the wind farm and residents’ observations, but found correlation of the noise with the wind speed.
Commenting on the study, Andrew Richards, Executive Manager External Affairs, Pacific Hydro, said: “While we acknowledge the preliminary findings of this report, what they mean at this point in time is largely unclear. In our view, the results presented in the report do not demonstrate a correlation that leads to the conclusion that there is a causal link between the existence of infrasound frequencies and the ‘sensations’ experienced by the residents.
“At the same time, the report states that further, scientifically robust study on these findings is required, given that the study was based on a small sample, and that there are inherent difficulties in previous acoustic studies of infrasound frequencies with respect to reliable instrumentation/frequency response.
“Pacific Hydro conducted this study to see whether we could establish any link between certain wind conditions or sound levels at Cape Bridgewater and the concerns of the individuals involved in the study.
“Steven Cooper shows in his report, for the limited data set, that there is a trend line between discrete infrasound components of the blade pass frequency (and harmonics of the blade pass frequency) and the residents’ sensation observations, based on his narrow band analysis of the results. However, we do not believe that the data as it currently stands supports such a strong conclusion.
“We would like to thank Steven Cooper and his team at The Acoustic Group for their exhaustive efforts in conducting this study and the development of the report.
“We would also like to thank the six residents for the valuable contribution they have made to the study.”
The report has been sent to a range of stakeholders, including government departments, Members of Parliament, environmental organisations and health bodies.
The report is available here.