PROSPECTIVE NOISE IMPACT ASSESSMENT OF EXTERNAL NOISE SOURCES
– Are you planning a new highway and want to assess the noise impact on the local environment?
– Are you looking to reduce noise within the borough and need technical support?
– Are you planning a new external amenity area and want to assess the best measures to reduce noise?
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Did you know that in 2010 in Portugal over 811k individuals were exposed to noise levels above the limits for sensitive areas such as residential areas, schools or hospitals?
Environmental noise impact assessments can be typified in the following phases (might not all be requires depending on the purpose of the assessment):
1. Description of the existing local acoustic environment;
2. Identification of assessment criteria;
3. Prediction of impacts;
4. Impact assessment;
5. Noise reduction measures.
1. Description of the existing local acoustic environment
Noise monitoring is required for the description of the existing scenario. The index for monitoring external noise is the equivalent continuous noise level, LAeq,T expressed in dB(A). The monitoring periods are chosen such that all major changes in noise emission and noise transmission are included. The best monitoring location, focusing on the sensitive receivers, is chosen on a case by case basis depending on the distribution of noise levels throughout the area. The project area of influence depends on its characteristics, being recommended that a cartographic characterization of the existing situation is done. A few hundred meter radius from the proposed development boundaries should be sufficient for most fixed installations. The most relevant existing noise sources should be identified (traffic noise, railway noise, aircraft noise, industrial noise, etc.) as well as sensitive occupations (residential, schools, hospitals, amenity areas used by the local population for resting).
2. Identification of assessment criteria
The assessment criteria are determined from the adaptation of the legal requirements set in the RGR for noisy activities and for transport facilities, and from the application of the environmental impact concept. The installation and operation of permanent noise producing activities in areas classified as sensitive is not allowed; small commercial and services facilities that do not operate during the night-time period and that are destined to serve the local population are excluded. During the construction phase, construction works can be classified as temporary noisy activities – in accordance with n.º 14 of the RGR such activities are blocked in several situations.
3. Prediction of impacts
The assessment critical path is the prediction of noise levels. The most relevant feature to take into account is that, in open space, noise propagation decreases with the distance to the noise source. Basically, two types of noise source should be considered, the point source and the line source, for which the propagation of noise waves is semi-spherical or semi-cylindrical, respectively.
4. Impact assessment
The comparison between the predicted noise levels with the identified assessment criteria allows for the determination of the development impact magnitude. A development may only be approved if its environmental noise impact is within the noise pollution legal requirements. Where the assessment indicates a risk of the legal requirements to be breached, it is concluded that there will be a significant noise impact. Critical situations must be clearly identified and are required to be subject to mitigation measures. Boundary situations should also be object of special attention, particularly due to the uncertainties of prediction methods.