November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

Table B1. Method for determining the tenth percentileStep 1Step 2Step 3Sort the L A90,15 minutedata in each assessment period in ascending order.Work out the tenth per cent position of the number of samples in the assessmentperiod. This can be calculated by multiplying the number of L A90, 15 minutevalues in theassessment period by 0.1.Determine the tenth percentile (essentially the lowest tenth per cent value):If the tenth per cent position (from Step 2) is an integer, then the tenth percentile isdetermined by taking the arithmetic average of the value of the L A90, 15 minuteat the tenthper cent position and the next highest value.If the tenth per cent position (from Step 2) is not an integer, then the tenthpercentile is the next highest L A90, 15 minutevalue above the value at the tenth per centposition.Examples:1. For a data set of size 40, the tenth per cent position is 4 (i.e. 0.1 x 40). As this isan integer, the tenth percentile is the average of the values at the 4th positionand the 5th position, counting from the lowest value of the sorted data (fromStep 1).2. For a data set of size 44, the tenth per cent position is 4.4 (i.e. 0.1 x 44). As thisvalue is not an integer, the tenth percentile is the value at the 5th positioncounting from the lowest value of the sorted data (from Step 1).2. Determine an assessment background levelfor each day (0700 to 1800), evening (1800 to2200) and night (2200 to 0700), using thetenth percentile method (essentially representsthe lower tenth percent value). Thetenth percentile method may be determinedautomatically using a spreadsheet package,or manually by applying the method shownin Table B1.3. Determine the rating background level to beused for assessment purposes. This is takento be the median value of the correspondingday/evening/night assessment backgroundlevels. For example, for a week’s worth ofmonitoring, the evening rating backgroundlevel is the median of the seven eveningassessment background levels—that is, thefourth highest (or lowest) value. Where thislevel is found to be less than 30 dB(A), therating background level is set to 30 dB(A).B2Short-term background noisemethodThe short-term method is the more appropriatebackground noise monitoring technique for:• establishing the difference between thebackground noise level and the source beingmeasured• checking the noise compliance of adevelopment• determining the effect of background noise ona source-noise measurement.B2.1 Instrumentation requirements andsitingTo measure background noise levels, use a soundlevelmeter that meets the specifications of a precision(Type 0 or 1) or general-purpose (Type 2)sound-level meter as stated in the AS 1259. Fit awindshield over the microphone before taking anymeasurements. If equipment other than a soundlevelmeter is used, the resulting measurementshould be at least as accurate as a measurementmade with a sound level meter as specified above.The equipment should have a current laboratorycalibration certificate or label in accordance withthe calibration requirements outlined in AS1259and AS2659. Equipment should also be calibratedin the field in accordance with the standards. Use aportable sound-level calibrator (in current calibration)for field-checking purposes.Wind speed during monitoring should be less than5 m/s (equivalent to number 3 on the Beaufort windscale—that is, leaves and small twigs in constantmotion; wind extends small flag).NSW industrial noise policy70