Page 242 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Obtaining a Construction Permit 215

residential neighborhood, then the permissible noise level is 60 dB. If both the source
and the receptor are located in an industrial area, then the permissible noise level is
70 dB. The Seattle ordinance also specifies noise thresholds for residential receptors
during critical evening and weekend hours that are approximately 10 dB lower than the
thresholds that are enforced during daytime hours.
Local regulations may also address critical period noise by specifying a daily
weighted average noise threshold, in addition to identifying a peak daytime noise
threshold. The daily weighted average threshold may account for source activities over
a 24-hour period, but place a higher weighting value on those activities that occur
during critical evening and early morning hours. The county of San Diego, California
enforces a noise ordinance that limits peak noise exposure in a mixed-use land applica-
tion to 50 dB from 7:00 a.m. to 10:00 p.m. and 45 dB for the remainder of the day on a
1-hour average, but also specifies a 24-hour weighted average limit of 10 dB for some
locations. Because of the 24-hour weighted average limit, plants that are operated con-
tinuously would have to be designed to more stringent standards than similar plants
that operate only a few hours per day.

Noise Mitigation
Engine manufacturers can provide various levels of silencing systems that significantly
reduce noise levels. Exhaust stacks of gas turbines can also be designed with noise
silencing features. The height of gas turbine exhaust stacks also helps to lessen the impact
of turbine combustion-related noise on ground-level receptors. Exhaust devices alone
may not successfully abate noise impacts. Other components of CHP systems such as
pumps, compressors, fans, and air handling equipment also contribute to noise levels.
The project engineer must also consider these sources when designing the plant. Ensuring
ample distance between sources and receptors is critical to mitigating noise levels. Enclo-
sures or other noise barriers may also be needed to comply with local noise limits.

Hazardous Material Transport and Storage
CHP plants that rely upon liquid fuel, such as diesel fuel or liquid propane gas, will also
rely upon the transportation and on-site storage of these fuels. Some CHP plants will
utilize SCR to reduce NO emissions. If the CHP system utilizes a gas turbine, the SCR
x
system may use aqueous ammonia as a reactant that will have to be transported to the
facility and stored until it is used. CHP facilities also utilize other hazardous materials
such as solvents, lubricants, and coatings. The project engineer or developer should be
aware of the potential environmental risks of transporting and storing these materials
and address these concerns during the application process.

Liquid Fuel Storage
While diesel fuel has a relatively low flash point and does not pose significant risk of
explosion, it does pose a risk to water resources, should it be spilled. A risk manage-
ment plan may be required to ensure that secondary containment will be incorporated
into the storage system to ensure that if a spill occurs, it can be recovered and will not
otherwise enter the surface or groundwater systems. Impervious pavement may also be
required at the point where fuel transfer occurs to prevent transfer to aquifers. Facility
grades and rainwater collection systems also have to be designed to prevent contami-
nated storm water runoff to surface water systems.