Azura-Edo Independent Power Plant Environmental Impact ... - IFC

The USEPA state that precipitation of greater than 0.2 mm/h will affectively
attenuate dust and wind speeds of >5.3 m/s are typically required to lift dust
from open surfaces. This will be lower for dust generated by mechanical
means (ie during excavation and due to the movement of vehicles over
unpaved surfaces), at around 3 m/s. Taking this into account, the following
can be concluded:
• At all but the most extreme wind speeds, dust will typically travel a
maximum of 200 m from source before falling from the air column (IFC,
2007);
• At the highest wind speeds, dust is unlikely to travel more than 500 m
from source; and
• Precipitation will effectively attenuate dust, with rainfall of >0.2 mm/h
likely to effectively attenuate dust emissions.
The assessment of the potential for significant dust nuisance to arise is
undertaken with due consideration of these weather factors, the proximity of
receptors to dust sources and the duration of dust generation activities. On the
basis of these factors the risk matrix set out in Table 7.7 has been developed.
Table 7.7
Dust Nuisance Assessment Matrix
Likely magnitude of
impacts
Likely major significant
impact
Likely moderate significant
impact
Likely minor significant
impact
Conditions
• Dust generating activities for >12 months
• Receptor within 200 m of dust source
• Downwind for >10 percent of the year where wind and
rainfall conditions promote dust generation
• Dust generating activities for 10 percent of the year where wind and
rainfall conditions promote dust generation
• Dust generating activities for 12 months
• Receptor within 500 m of dust source
• Downwind for 2-5 percent of the year where wind and
rainfall conditions promote dust generation
Insignificant impact • Receptor > 500 m of dust source
• Receptor 200 m – 500 m from dust source
• Downwind for