Our Environment - Mining and the Environment: From Ore to Metal - page 296

TABLE 7.1
Human Reaction to Increases in Sound Pressure Levels - Absolute sound level is not the only determinant of
effect; increases in sound pressure level above ambient levels at the chosen point of sound reception are equally important

Increase in Sound Pressure (dB) Human Reaction

Under 5 Unnoticed to tolerable

5-10 Intrusive

10-15 Very noticeable

15-20 Objectionable

Over 20 Very objectionable to intolerable

Source:
Down and Stocks (1978)

one sound has twice the energy but lasts half as long, the two sounds would be character-
ized as having the same equivalent sound level. Equivalent Sound Level is considered to
be directly related to the effects of sound on people since it expresses the equivalent mag-
nitude of the sound as a function of frequency of occurrence and time. By its derivation
Leq does not express the maximum or minimum sound pressure levels that may occur in a
given time period. These maximum and minimum sound pressure levels should be given
in the noise analysis. The time interval over which the Leq is measured should always be
given. It is generally shown as a parenthetic; Leq (8) would indicate that the sound had
been measured for a period of eight hours.
It is important to have an understanding of the way noise decreases with distance. The
decrease in sound level from any single noise source normally follows the 'inverse square
law'. That is, sound pressure level changes in inverse proportion to the square of the dis-
tance from the sound source. Moisture, temperature, and wind all influence the propaga-
tion of sound levels, but their influence is minor and time dependent, usually neglected in
environmental assessment.
Most humans find a sound level of 60 to 70 dB(A) as beginning to create a condition of sig-
nificant noise effect (USEPA 550/9-79-100, November 1978). However, absolute sound level
is not the only determinant of effect; increases in sound pressure level above ambient levels at
the chosen point of sound reception are equally important. Increases ranging from 0 to 6 dB
should have no appreciable effect on receptors ( Table 7.1 ). Sound pressure increases of more
than 6 dB may require a closer analysis of impact potential, depending on existing sound
pressure levels and the character of surrounding land use and receptors. Sound pressure level
(SPL) increases approaching 10 dB result in a perceived doubling of SPL. The perceived
doubling of the SPL results from the fact that SPLs are measured on a logarithmic scale.

Most humans fi nd a sound level
of 60 to 70 dB(A) as beginning to
create a condition of signifi cant
noise effect.

7.2 THE LITHOSPHERE - GEOLOGY, LANDFORM,
AND EARTH RESOURCES

The ores that we exploit are all located in the upper part of the Earth's crust - the litho-
sphere. Accordingly the nature of the land is of fundamental importance to any mining
project. Geology, landform, soils, land quality, and land use all represent important char-
acteristics which influence mine development and may be affected, temporally or perma-
nently, by project operations.

The nature of the land is of
fundamental importance to any
mining project.