November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

4 ‘Modifying factor’ adjustments4.1 IntroductionWhere a noise source contains certain characteristics,such as tonality, impulsiveness, intermittency,irregularity or dominant low-frequency content,there is evidence to suggest that it can cause greaterannoyance than other noise at the same noise level.On the other hand, some sources may cause lessannoyance where only a single event occurs for alimited duration. This section outlines the correctionfactors to be applied to the source noise level at thereceiver before comparison with the criteria specifiedin Section 2 to account for the additional annoyancecaused by these modifying factors. The correctionfactors listed below were determined followinga review of Australian and overseas practices andthe relevant literature.The modifying factor corrections should be appliedhaving regard to:• noise from all sources, individually and incombination, that contribute to the total noiseat a site; and• the nature of the noise source and itscharacteristics.Table 4.1 sets out the corrections to be applied. Thecorrections specified for tonal, impulsive, intermittentand low-frequency noise are to be added to themeasured or predicted noise levels at the receiverbefore comparison with the criteria.4.2 Definitions to support themodifying factor correctionsTonal noise—containing a prominent frequencyand characterised by a definite pitch.Low-frequency noise—containing major componentswithin the low frequency range (20 Hz–250Hz) of the frequency spectrum.Adjustment for duration—applied where a singleeventnoise is continuous for a period of less thantwo and a half hours in any 24-hour period. Theacceptable noise level may be increased by theadjustment shown in Table 4.2. This adjustment isdesigned to account for unusual and one-off events,and does not apply to regular high-noise levels thatoccur more frequently than once per day.Maximum adjustment—the maximum correction tobe applied to the criteria or the measured levelwhere two or more modifying factors are present.The maximum adjustment is 10 dB(A) where thenoise contains two or more modifying factors(excluding the duration correction).4.3 Applying the modifying factorsThe modifying factors are to be applied to the noisefrom the source measured/predicted at the receiverand before comparison with the criteria. The modifyingfactor correction is applied as follows (K iisequal to the modifying factor correction (from Table4.1)):CriterionMeasured orPredictedCompareCriterionValueIntrusiveness L Aeq, 15 minuteplus K iRatingbackgroundlevel plus 5Amenity(including hightraffic criterionSection 2.2.3)L Aeq, periodplus K iAcceptablenoise levelWhere two or more modifying factors are present,the maximum correction is limited to 10 dB.Impulsive noise—having a high peak of shortduration or a sequence of such peaks.Intermittent noise—the level suddenly drops to thatof the background noise several times during theassessment period, with a noticeable change innoise level of at least 5 dB.NSW industrial noise policy28