November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

E3.1 Pasquill-Gifford schemeThe Pasquill-Gifford scheme, outlined in Table E3,essentially determines Pasquill stability categoriesbased on hourly or three-hourly wind-speed andcloud-cover measurements. Once these are known,the percentage frequency of temperature inversionsover the three winter months may be predictedusing the relationship in Table E1. The followingdata are required for the analysis collected over thethree winter months:• hourly or three-hourly wind speed anddirection at 10 m (the wind direction is notrequired to determine the Pasquill Stabilitycategory but is required for the noiseanalysis)• hourly or three-hourly cloud covermeasurements• times of sunrise and sunset recorded on adaily basis (these times are required to definethe night-time period) or assumed to be 7 amand 6 pm, respectively.The required data may be obtained from the Bureauof Meteorology from data collected at the closestmonitoring station. The parameters needed areavailable from selected Bureau of Meteorologystations across NSW. Wind speeds and winddirections are subject to considerable local variation.However, cloud cover is generally not subject tosuch strong spatial variations and, consequently,data from a station some distance away may beacceptable. Whether or not data apply to a particularsite needs to be critically assessed. For cloudcover, distance from the coast and ground elevationwill have an important bearing on the cloudiness. Ingeneral, data collected from weather-monitoringstations are considered relevant for a radius of30 km from the station, provided the surroundingarea is in the same topographical basin as thestation.If representative cloud data are not available from anearby station, it is advisable to use the sigma-thetamethod outlined in Section E4 instead to determinestability categories. This is because the numerousindividual observations needed to measure cloudcover for the Pasquill-Gifford method are often notfeasible.E3.1.1 Determining the frequency of occurrence ofinversionsOnce the stability categories have been determinedfor all the data collected during the period from6 pm to 7 am, the percentage occurrence of moderateand strong inversions occurring during F and Gstability categories, respectively, may then bedetermined. The percentage occurrence requiredhere is the total percentage occurrence for thenight periods over the three months of winter. ThePasquill-Gifford scheme assumes that moderateand strong inversions do not occur during thedaytime hours (considered here to be from 7 am to6 pm).Where the sum total of F and G inversions occur forat least 30 per cent of the total night-time in winter,the project area is considered to be significantlyaffected by inversions warranting noise assessment.Default values to be used when assessing theimpact on noise caused by temperature inversionsduring F and G stability conditions are presented inSection E6. The F-category default values are to beused in noise prediction where a combination of F-and G-category inversions is predicted. The G-category default values are to be used in noiseprediction only where G-category inversions arepredicted for at least 30 per cent of the total nighttimein winter.E3.2 Turner schemeThe Turner scheme recognises that stability near theground depends mainly on net radiation and windspeed, with net radiation being a function of cloudcover and the height of the cloud ceiling. Thisscheme determines stability categories based onhourly or three-hourly wind measurements of cloudcover, cloud-ceiling height, wind speed and winddirection. As with the previous scheme, the percentageoccurrence of temperature inversions over thethree winter months may be predicted using therelationship in Table E1. The following data need tobe collected over the three winter months for analysis:• hourly or three-hourly wind speed anddirection at 10 m (wind direction is notrequired to determine the Pasquill Stabilitycategory, but is required for the noiseanalysis)• hourly or three-hourly cloud covermeasurementsNSW industrial noise policy80