November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

which is from 10 pm to 7 am.) Winter is selected asthe appropriate season in which to determinewhether temperature inversions are significant, as itrepresents the season with the highest frequency ofoccurrence of temperature inversions.Default values for temperature inversions anddrainage-flow wind speed are provided for use inassessing impacts where inversions are present forat least 30% of the total night time during winter.Alternatively, actual inversion strength and windspeed values based on on-site measurements may beused instead of the default values.A brief description of the main components of theprocedure for assessing noise increases due toinversion effects is presented below. Details of thefull procedure are presented in Appendix C.Step 1:Do initial screening testsTo assess the level by which noise is increased as aresult of inversion effects, it is generally necessary toanalyse meteorological data from the area in question.However, before doing any detailed analyses,the potential for temperature inversions to increasenoise impact should be determined. Detailedanalyses of meteorological data are not requiredwhere there is little or no potential for impact, as inthe following cases:• where the development in question does notoperate during the night-time hours. Astemperature inversions are usuallyprominent during night-time hours, there isno need to consider their effects for adevelopment that does not operate at night(10 pm to 7 am)• where, by using the default values, (seeAppendix C Table C1 for screening test defaultvalues), it can be shown that there would beno significant additional noise impactsduring inversion conditions (for example,less than a 3-dB increase). In this situation,no further analysis of inversion effects isrequired. Situations where this could occurinclude:—areas that experience only a slight increasein noise due to inversions—areas where the most-affected premisesmay be located close to the development,thus negating the effects of inversionsStep 2:(which focus noise at relatively largedistances).Determine the significance oftemperature inversionsWhere screening tests (Step 1) indicate that inversionscould have a significant impact on noise, theproponent may want to do further analyses toconfirm whether the occurrence of temperatureinversions at the locality is significant. This wouldinvolve determining the percentage occurrence ofmoderate and strong inversions during winter,based on existing meteorological data and usingany one of the methods outlined in Appendix E.(Weak inversions are not included, as they are notconsidered to have a significant impact on noise.)Where inversion conditions are predicted for atleast 30% (or approximately 2 nights per week) ofthe total night time in winter, then inversion effectsare considered to be significant and should be takeninto account in the noise assessment.In NSW, the Hunter region has been identified as anarea often affected by temperature inversions. Forthis reason, the Hunter has been studied in detail,and the percentage occurrence of temperatureinversions has been determined for the entire regiondown to a 2-km grid-square resolution. (See AppendixF.)Step 3:Decide on inversion parametersto useThere are two options: use the default parametersspecified, or use parameters determined by directmeasurement.A. Using default inversion parametersDefault values for inversion strength and windspeed have been specified for use in the noiseassessment to avoid the need for potentially costlyon-site monitoring. These default values have beenchosen based on the analysis of available field data.Essentially, the following default parameters arespecified for non-arid and arid areas:Non-arid areas (annual average rainfall greater than500 mm):Moderate (F-class stability category) inversions• 3 °C/100 m temperature inversion strengthfor all receivers, plus a 2 m/s source-to-NSW industrial noise policy33