November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

• hourly or three-hourly cloud ceiling-heightmeasurements• daily records of time of sunrise and sunset(needed to define the night-time period) orassumed to be 7 am and 6 pm, respectively.Similarly, the required data may be obtained fromthe Bureau of Meteorology from data collected at theclosest monitoring station. (See Section E3.1 considerationsrelating to the applicability of data to a site.)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 large numberof individual observations needed to measure cloudcover for the Turner scheme may not be feasible.Table E4 gives the stability class as a function ofwind speed and net radiation. The net radiationindex for the night period ranges from –1 to –2(negative radiation is radiation directed away fromthe earth). Note that the Turner scheme assumesthat moderate and strong inversions do not occurduring daytime hours (considered here to be theperiod from 7 am to 6 pm).Note also that, in the specifications for this scheme,cloud-cover data are assumed to be available in1/10 ths . Usually data from the Bureau of Meteorologyare reported in 1/8 ths , so some conversion willneed to be done.Table E4. Stability class as a function ofnet radiation and wind speedWind speedNet radiation indexknots m/s 0 –1 –20–1 0–0.7 D F G2–3 0.8–1.8 D F G4–5 1.9–2.8 D E F6 2.9–3.3 D E F7 3.4–3.8 D D E8–9 3.9–4.8 D D E10 4.9–5.4 D D E11 5.5–5.9 D D D≥ 12 ≥ 6.0 D D DThe net radiation index to be used in Table E4 is:1. If the total cloud cover is 10/10 and theceiling is less than 7000 feet, use net radiationindex equal to 0 (whether day or night).2. For night-time (from 6 pm to 7 am):—If total cloud cover ≤ 4/10, use net radiationindex equal to –2.—If total cloud cover >4/10, use net radiationequal to –1.Follow the procedure outlined in Section E3.1.1 todetermine the percentage occurrence of temperatureinversions once the stability-category classificationshave been made.E4Use of sigma-theta dataThe sigma-theta method, developed by the US EPA,refers to observations of sigma-theta, wind speedand time of day. With this method the Pasquillstability categories may be determined by using arelationship between stability categories and thestandard deviation of the horizontal wind directionfluctuations (σ Ain degrees). The scheme is appliedin one step to determine the daytime stabilitycategory and two steps to determine the night-timestability category as follows:• the daytime (from 7 am to 6 pm) stabilitycategory may be determined directly from σ Adata using Table E5• the night-time (from 6 pm to 7 am) stabilitycategory may be determined in two steps:—determine the stability category from σ Adata using Table E5.—modify this stability category based onprevailing wind speed using Table E6.Sigma-theta data may be measured on an hourly orthree-hourly basis and should be collected asspecified in Australian Standard AS–2923.NSW industrial noise policy81