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Some gases
in the atmosphere affect the Earth’s heat balance by absorbing infrared radiation.
These layers of gas in the atmosphere can
prevent the escape of heat in much the same way as glass in a greenhouse. Thus, global warming is often referred to as
the “greenhouse effect.” The gases most responsible
for global warming are referred to as greenhouse gases (GHG). It is becoming more widely accepted that continued
increases in GHGs will contribute to global warming, although there is uncertainty
concerning the magnitude and timing of the warming trend. Combustion of fossil fuels during a gas project
construction and operation will result in the emission of the following GHGs: carbon
dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Emissions of GHGs are typically expressed in terms
of CO2 equivalents (CO2e), where
the potential of each gas to increase heating in the atmosphere is expressed as a multiple of the
heating potential of CO2, or its global warming potential.
GHG emissions,
expressed in terms of CO2e, typically must be estimated for both compressor station
operation and construction. The proposed
Project is not subject to the newly revised PSD regulations applicable to GHGs.
Known as the “Tailoring Rule”, this regulation
sets a higher major source threshold than other pollutants. Typically, the estimated potential GHG emissions
are less than the threshold amount.
Another new
regulation which specifically targets GHGs is the Mandatory Reporting Rule, codified
under 40 CFR Part 98. As a natural gas transmission
compressor station, the station may potentially be applicable to Subpart C (stationary
combustion) and Subpart W (Oil and Natural Gas Systems) of the rule. Subpart C covers fuel combustion in the compressor
turbines (the two Solar Centaur 50 turbines) and the fuel gas heater. All compressor stations (at least the new
ones) include emergency generators. The emergency
generator is not included in the emission calculations, as it is used as an emergency
unit. Subpart W covers venting of the compressor
turbines, venting of condensate storage tanks, station blowdown venting, and equipment
leaks from piping components. The rule requires
monitoring and reporting if an applicable source emits greater than actual emissions
of 25,000 metric tons of GHGs from certain source categories.
Construction
Emissions
Construction
of the Gas Compressor Station will result in temporary increases in emissions of
some pollutants due to the use of construction equipment powered by diesel or gasoline
engines. Construction activities will also
result in the temporary generation of fugitive dust due to disturbance of the surface
and other dust generating actions. Indirect
emissions during the construction period will be associated with delivery vehicles
and construction worker commuting.
The quantity
of fugitive dust generated depends on the size of area disturbed and the intensity
of construction activity and also on the silt and moisture content of the soil,
the wind speed, and the speed, weight, and volume of vehicular traffic. Fugitive dust emissions will be mitigated, as necessary,
by spraying water to dampen the surfaces of dry work areas. Worst-case fugitive particulate matter emissions
for PM10 and PM2.5 were calculated based on EPA AP-42 recommended emission factors
for heavy construction activities along with estimates of the extent and duration
of active surface disturbance. The use of
the heavy construction emission factor from AP-42 is meant to be general in nature
to cover a wide range of construction operations. This may overestimate potential fugitive dust generated
by the proposed construction project. The
estimated emissions are summarized in tables and supporting calculations are
provided in the appendices.
Emissions
of NOx, CO, PM10, PM2.5, SO2, VOCs and Greenhouse Gases (GHGs) from construction
equipment engines used during Project construction have been estimated based on
the anticipated types of non-road and on-road equipment and their levels of use.
Emission factors for diesel and gasoline
on-road vehicles were obtained using EPA’s MOBILE6.2 model (SO2) and from New York
State Department of Transportation (NYSDOT)
tables developed using MOBILE6.2
(NOX, CO, VOC,
PM10, PM2.5).
Emission factors
for diesel and gasoline non-road equipment engines were obtained using EPA’s NONROAD
model documentation. Emission factors using
Tier 2 diesel engine standards have conservatively been assumed to apply to construction
equipment engines during 2012 and do not reflect the anticipated phasing-in of more
stringent emissions and fuel standards. A Table typically presents these emission estimates
by major construction activity for the entire construction period for all construction
activities, respectively. The assumptions,
data, and emission factors used to estimate emissions from construction equipment
engines and vehicles are provided in Appendices, along with more detailed listings
of emissions estimates.