November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

Appendix EMethods for determining the frequencyof temperature inversionsE1BackgroundAn important part of the assessment of noiseenhancement due to inversions involves determiningwhether inversions occur frequently enough towarrant inclusion in the assessment. It is consideredunreasonable to expect a development tocomply with noise limits under inversion conditionsif inversions occur infrequently.The frequency of occurrence of temperature inversionsmay be determined either by direct measurementof inversion parameters, or by using indirectmethods that allow the prediction of wind andtemperature profiles to within a moderately narrowrange using readily available meteorological data.The direct-measurement method will result inactual temperature gradients and drainage-flowwindspeeds from which the percentage occurrenceof inversions may be determined. The indirectmethods, on the other hand, allow the susceptibilityof an area to inversions to be determined throughthe use of the relationship developed by the USAtomic Energy Commission between atmosphericstability categories and inversions. The relationshipshown in Table E1 outlines the range of temperaturegradients that can be expected within each stabilitycategory. Hence, if a stability category is known,then the range of possible temperature gradientsmay be inferred.A positive temperature gradient signifies a temperatureinversion; hence, from the table below, inver-Table E1. Stability categories based onDT/DZStabilitycategoryRange of vertical temperaturegradient ( o C/100 m)A DT/DZ < –1.9B –1.9 ≤ DT/DZ < –1.7C –1.7 ≤DT/DZ < –1.5D –1.5 ≤ DT/DZ < –0.5E –0 .5 ≤ DT/DZ < 1.5F 1.5 ≤ DT/DZ < 4.0G4.0 ≤ DT/DZsions occur during E, F and G stability categories.These three categories are considered to representweak, moderate and strong inversions respectively.For noise-assessment purposes, only moderate andstrong inversions are considered significant enoughto require assessment.Three basic schemes may be used to determine theoccurrence of different stability classes at a particularsite based on the following combinations ofmeteorological parameters:1. Direct measurement of temperature lapse rateover the height interval range of 1.5 to 10 mand 50 to 60 m, and wind speed at 10 mheight.2. Cloud cover, wind speed and solar elevation(Pasquill-Gifford scheme and Turner scheme).3. Measurements of sigma-theta (the standarddeviation of wind direction), wind speed andtime of day.All methods involve analysing three months ofmeteorological data collected in winter—the seasonduring which most inversions occur. Wind measurementsare to comply with AS 2923, Ambient Air—Guide for measurement of horizontal wind for air qualityapplications.E2Direct measurement oftemperature lapse rateThis method involves the measurement of temperaturegradient and wind speed at hourly intervalsover the three winter months. The temperaturegradient measurement involves measuring temperatureat two elevated levels (1.5 to 10 m and 50 to 60m) over a 50-m height interval to determine thetemperature difference. The temperature gradient isthen the temperature difference (that is, the temperatureat the higher elevation minus the temperatureat the lower elevation) divided by the height difference.The wind speed should be measured at aheight of 10 m. Care should be taken to ensure thatmeasurement procedures comply with relevantstandards.NSW industrial noise policy78