November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

3 Determining existing noise levels3.1 Determining background noise forthe intrusiveness criterionThe background noise level is defined here as ‘theunderlying level of noise present in ambient noisewhen all unusual extraneous noise is removed’.Sound levels contributing to background levels caninclude sound from nearby traffic (see Section 3.1.3),birds, insects, animals, machinery and similarsources if these sounds are a normal feature of thelocation. The background noise level is consideredto be represented by the L A90,15 minutedescriptor. Incomparison, the rating background level (as definedin Section 3.1.2) is the single-figure backgroundnoise level derived from monitoring L A90, 15 minutesovera representative period of time. The rating backgroundlevel is used for assessment purposes.Background noise levels need to be determinedbefore intrusive noise can be assessed. The backgroundnoise levels to be measured are those thatare present at the time of the noise assessment andwithout the subject development operating. Hence,for the assessment of modifications to an existingdevelopment, the noise from the existing developmentshould be excluded from background noisemeasurements.When assessing a new development, it is importantto undertake sufficient monitoring of backgroundnoise to allow intrusive noise to be assessed adequately.However, when assessing noise levels inresponse to complaints, the background noise levelduring the period of the complaint is of interest, andmonitoring over a shorter length of time may beappropriate.Before embarking on a noise-monitoring program,the potential for the development/ activity to causenoise annoyance, and the need for accurate noiseassessment, should be considered. Two measurementregimes are presented below. The first is adefinitive method to be used when assessing developmentswith the potential for significant noiseimpact. The second is a shorter method that can beused for complaint-assessment purposes.3.1.1 Methods of determining backgroundnoiseTable 3.1 summarises the two procedures for determiningbackground noise: the long-term method tobe used at the planning and approval stage, and theshort-term method for complaint and complianceassessment purposes. The long-term method involvesa two-step process to determine the ratingbackground level. The short-term method involvesonly one step. Appendix B gives a detailed descriptionof instrumentation requirements, and proceduresfor measurement and analysis for eachmethod.The long-term method for determining backgroundnoise (summarised in Table 3.1) is designed toensure that the criterion for intrusive noise will beachieved for at least 90% of the time periods overwhich annoyance reactions may occur (taken to beperiods of 15 minutes).Definitions and technical considerations to helpusers interpret and apply the methods are set downin the following sections.3.1.2 Definitions to support methodologiesExtraneous noise—noise due to activities that arenot typical of the area. These activities might includeconstruction, changes in road, rail or air traffic dueto holiday periods, and special events such asconcerts or sporting events. Normal daily roadtraffic and other transportation noise are not consideredto be extraneous noise. Where an industry in anindustrial estate wishes to extend its operations, themeasured background noise level may include thegeneral hum of industries nearby, but should notinclude any noise from the site itself—or noise fromany intrusive sources nearby that could affect theL A90,15 minutevalue. As a reasonable guide, any extraneousnoise present for at least half of a 15-minutemonitoring period, and having the potential to affectthe L A90,15 minutevalue, should be excluded.NSW industrial noise policy22