Page 240 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Obtaining a Construction Permit 213

Compliance Assessment
Once all of the technical analyses and assessments are complete, the applicant can pro-
ceed to conduct a regulatory compliance assessment. This assessment provides a more
detailed explanation of how the CHP project can be expected to comply with applicable
regulations. It takes into account the equipment selection, operating schedule and emis-
sions inventory. It also takes into account any additional analyses that may be required,
such as the air quality impact analysis and health risk assessment.
As the CHP project is further detailed and its operations better defined, various anal-
yses are conducted, and regulatory compliance is assessed. Accordingly it is likely that
certain additional mitigation measures may be needed to offset the project’s impacts.
Mitigation measures may include purchasing emission reduction credits to offset
increases from the project, the addition of emission control systems, voluntary reduc-
tions in operating hours or operating load, and the installation of higher-than normal
exhaust stacks to aid in exhaust plume dispersion. These measures should be anticipated
in planning for the regulatory analysis. In most cases both voluntary and mandatory
mitigation measures will be specified in permit conditions to ensure that the permitting
agency can enforce the project’s compliance with local regulations and policies.

Noise
Noise considerations are also critical to CHP projects. The permitting agency will typi-
cally have to ensure that the project does not result in noise levels that exceed local
ordinances or building codes, and that the CHP project does not otherwise cause a
nuisance to local residences and businesses. Combustion sources such as gas turbines
and reciprocating internal combustion engines can be significant sources of noise at a
CHP plant because large volumes of mixed air and engine or combustion turbine are
transported at a high velocity through the exhaust system to ambient. The mechanical
functions of engine or combustion turbine operation also add to projected ambient
noise. Ancillary devices such as compressors, pumps and air handling systems can also
contribute to higher ambient noise levels.
Noise Characteristics
Sound pressure, the acoustical energy emitted by the sound source, is the component of
noise that is measured and regulated. Sound pressure is measured in decibels (dB) and
reflects the force of the sound wave on a surface perpendicular to the sound. The
decibel scale is logarithmic with sound intensity increasing by a factor of 10, so small
increases in decibel represent much larger increases in sound intensity. Ten decibels is
10 times more intense than 1 dB, but 20 dB is 100 times more intense than 1 dB. While
the decibel system is an objective measurement of sound pressure, human perception
of sound (loudness) is subjective and is also restricted by sensitivity to particular
frequencies. To the human ear, each 10-dB increase in sound pressure generally seems
only twice as loud.
Table 12-3 summarizes the sound levels and effect of several typical sources. A
sound level of 10 dB is barely audible to the human ear. The noise from a source is
considered intrusive at a level of 60 dB, which is about the same level of noise that is
emitted by an air-conditioning unit. Extended exposure to sounds at 90 dB (the level
that is experienced near heavy vehicle traffic), can cause hearing damage. Pain and
irreversible hearing damage can occur if exposed to higher noise levels above 120 dB.