The Ambient Sound Level in AUC Rule 012
A revised version of Rule 012 came into effect on August 1, 2019. The revised version includes a new section (section 2.6) that deals with the ambient sound level in Alberta. The ambient sound level is used in NIA reports to establish the permissible sound level. Applicants are now required to assess the ambient sound level as part of an NIA, particularly in noisy or pristine environments. In section 2.6 “Pristine” is defined as areas where the nighttime ambient sound level might be less than 35 dBA. In the appendix to Rule 12 however a pristine area is defined as “A natural area that might have a dwelling but no industrial presence, including energy, agricultural, forestry, manufacturing, recreational or other industries that affect the noise environment”. Rule 012 does not provide guidance on how an assessment of the ambient sound level should be conducted. During the consultation for this revision of Rule 012 and the presentation of the revised Rule 012 by the AUC, dBA Noise Consultants Ltd and other practitioners commented on the proposed changes, including the requirement to include an assessment of the ambient sound level. It was also brought to the attention of the Commission that this requirement might give rise to discussions about the ambient sound level assumed in NIA reports.
In Decision 24401-D01-2019 of December 20, 2019 (Sharp Hills Wind Project Amendments) the Commission had the first opportunity to interpret the amendments in the 2019 version of Rule 012. The decision addresses challenges to the use of the assumed ambient sound level of 35 dBA in NIA reports. dBA Noise Consultant's Henk de Haan acted as expert witness for a group of concerned interveners. The NIA provided by the applicant did not include an assessment of the ambient sound level, and a nighttime value of 35 dBA was assumed. Based on both a desktop study and a 24 hour measurement survey at several interveners dBA Noise Consultants established a nighttime ambient sound level of approximately 27 dBA, considerably less than the 35 dBA assumed in table 1 of Rule 012.
Summarized, the Commission ruled that:
- Neither AER Directive 038 or previous versions of Rule 012 prohibited interveners from challenging the use of an assumed ASL when determining PSLs in a project area;
- The Commission's use of assumed ambient sound levels for rural areas is intended to provide a reasonable, consistent and practical mechanism for predicting and assessing cumulative sound levels;
- A proponent's obligation under section 2.6, under 5 of Rule 012 to demonstrate the reasonableness of using the assumed ambient sound level in rural areas where agricultural and/or Oil & Gas activities take place can be satisfied by documenting the presence of such activities.
- The Commission acknowledges that including different definitions of “Pristine" in section 2.6 and the glossary may cause confusion. The decision recommends referring in section 2.6 to the definition included in the glossary.
- Nonetheless, it remains open to interveners to challenge the use of assumed ambient sound levels by providing compelling evidence as well as measurement data in support of a Class A2 adjustment.
- A 24 hour survey is typically insufficient to characterize the ambient sound level in areas where it is not particularly noisy. The commission indicates that the appropriate duration for ASL surveys is case specific.
Readers are encouraged to read the full decision (24401-D01-2019) for themselves. It can be found on the AUC's website.