Comparison of methods for measurement of dust deposition in South African mining sectors

Abstract

Dust particles in the atmosphere are a key cause of nuisance, health and other environmental problems. The mining sector is a major source of airborne particulate matter caused by operations like terrain clearing, drilling, blasting, tipping and loading and the passage of vehicles on unpaved roads. The nuisance effect of airborne dust can be measured by using dust buckets and/or directional dust deposition gauges. Dust buckets are used to determine vertical dust deposition rates and directional dust deposition gauges are used to determine the direction of the sources. Traditionally the measurement of the vertical flux of dust, or dust deposition has been used as to indicate the nuisance caused by coarse suspended particulate matter. Several countries have produced standards for permissible dust deposition rates. Although alternative deposition measurement methods have been proposed, ASTM D1739 has remained the method most often used in the South African mining and industrial sectors to measure dust deposition. In addition, a number of non-standard directional dust deposition gauges have been used. SANS 1929:2005 (South African National Standards, 2005) prescribes the use of ASTM D1739:98 for measuring dust deposition. However, for historical reasons the previous version, ASTM D1739:70 (re-approved as ASTM D1739:82) is still widely used and in the recently promulgated South African Dust Management regulations the use of this version is prescribed. In order to determine the difference in the results obtained by the two versions, ASTM D1739:82 and ASTM D1739:98 were used to measure dust deposition levels arising from a coal mining operation in the Mpumalanga Province and a gold mining operation in North-West Province. In order to determine whether a correlation exists between vertical dust flux (dust deposition) and horizontal dust flux, standard directional horizontal dust flux gauges according to BS 1747 part 5 were also set up at both sites. The measurement of dust deposition using three dust deposition gauges (i.e. ASTM D1739:82, ASTM D1739:98 and BS 1747 part 5, directional dust deposition gauges) was undertaken monthly over a period of fourteen (14) months at the two sites. The findings of the study indicate that the dust deposition rates for an opencast coal mine are generally higher than the dust deposition rates for an underground gold mine. ASTM D1739:98 was shown to be a more efficient dust deposition collection method than ASTM D1739:82, with the ratio between the mean values slightly more than 2. The addition of water to the dust bucket does not make a statistically significant difference to retention of dust in the bucket. There is a weak correlation between results for the vertical dust gauges and horizontal dust flux. It is recommended that the South African mining sector continue dust deposition monitoring and reporting using the more recent version of ASTM D1739, as high deposition levels may indicate a potential health impact from PM10 thoracic dust.