RANDOM BACKGROUND ON PSD
BACKGROUND

The Clean Air Act (CAA) established the PSD permit program to prevent areas that
currently have clean air from significant deterioration. The PSD permit program
limits emissions by requiring permits for major stationary air pollution sources.

The CAA created three air quality area classifications for air quality protection
programs: Class I, Class II, and Class III, and establishes allowable pollution
“increments” that may be added to the air in each area while still protecting air
quality.

Specific increments exist for particulate matter, nitrogen oxides, and sulfur dioxide.
The increments vary depending upon the pollutant and classification of an area.

The PSD permit program requires that available increments are not exceeded by
major stationary sources. The minor source baseline date is established by the first
major source permit application significantly affecting a baseline area. Once the
minor source baseline date is established, minor sources begin consuming increment.

After the minor source baseline date has been established, major stationary sources
must consider minor source growth in each baseline area and states must track minor
source increment consumption.

The state must design and implement a control plan if minor sources violate the
increment in a baseline area.

Section 107(d) of the Clean Air Act allows Governors to submit a list of areas designated
as either nonattainment, attainment, or unclassifiable for air quality planning purposes.
For example, areas designated as nonattainment require air quality control plans or
“SIPs” for the protection of public health and welfare because air quality standards have
been violated. Areas designated as attainment / unclassifiable are those areas generally
considered to meet or exceed air quality standards. Descriptions of these areas are
published in 40 CFR Part 81 as a matter of public record.

Congress directed EPA to promulgate rules to protect attainment / unclassifiable areas
from deteriorating into nonattainment areas. EPA developed a permitting program
called Prevention of Significant Deterioration, or “PSD”. The PSD permitting
program limits allowable increases in pollutant concentrations above certain levels
called ‘increments’. Allowable increments vary by location across the state. Areas
characterized as Class I, i.e., National Parks and Wilderness areas, allow less
incremental pollution growth; while areas characterized as Class II allow more.
States are required to track increment consumption to maintain PSD program
compliance.
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
For increment tracking purposes, the PSD permitting program creates “baseline
areas,” which are those areas of modeled 1µ/m3 impact for a major stationary source
locating in an attainment / unclassifiable area. States are required to track increment
consumption in these baseline areas. EPA interprets baseline areas as those defined
as attainment / unclassifiable in 40 CFR Part 81 i.e., “Rest-of-State” designations.

A baseline area is defined as an area located in an attainment / unclassifiable area in
which a proposed major stationary source or modifications has a 1µ/m3 impact.
MAJOR SOURCE BASELINE DATES: Actual emission increases from major
stationary sources occurring after the dates below are considered to consume available
increment. Actual emissions occurring before these dates are not considered to consume
increment, but are captured as ‘background.’
Reference 40 CFR 52.21 (14) (i).
PM-10 and SO2 --> January 6, 1975;
NO2 --> February 8, 1988.
MINOR SOURCE BASELINE DATES: Actual emission increases from minor
stationary sources and other types of sources such as vehicle tailpipe, road dust,
agricultural, etc. are not considered to consume increment until the major source baseline
date is triggered for an area.
The definition of ‘trigger’ is the date at which increment tracking must begin in a
baseline area. The minor source baseline date is triggered by the first complete PSD
permit application for a source which locates in, or significantly impacts a baseline area.
This is determined by the first major source PSD application received by the state after
the following federal baseline dates:
PM-10 and SO2 -> August 7, 1977;
NO2 -> February 8, 1988.
NATIONAL IMPORTANT DATES:
Increased emissions from major stationary sources occurring after the dates set
forth below consume increment. These are dates established by rule 40 CFR 52.21
(a)(14)(i):
Pollutant
PM-10
Major Source Baseline Date
January 6, 1975
SO2
January 6, 1975
NOx
February 8, 1988
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Emissions from minor sources consume increment after the date of submission of
the first complete PSD permit application following the dates set forth below. These
are dates established by rule 40 CFR 52.21 (a)(14)(ii):
Pollutant
PM-10
Minor Source Baseline Date
August 7, 1977
SO2
August 7, 1977
NOx
February 8, 1988
MONTANA IMPORTANT DATES:
The major source permit submissions that established the minor source baseline
date are set forth below:
Source
MPC - Colstrip
Pollutant
PM-10
Permit Application Date
March 26, 1979
MPC - Colstrip
SO2
March 26, 1975
NOx
NOx
January 10, 1990
INCREMENT BY CLASS
The following shows the increments allowed over baseline concentrations in Class I
areas (40 CFR 52.21):
Pollutant
Increment
PM-10
Annual arithmetic mean
4
8
24 hour maximum
SO2
Annual arithmetic mean
24 hour maximum
3 hour maximum
NOx
2
5
25
2.5
Annual arithmetic mean
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The following shows the increments allowed over baseline concentrations in Class II
areas*:
Pollutant
Increment
PM-10
Annual arithmetic mean
17
30
24 hour maximum
SO2
Annual arithmetic mean
24 hour maximum
3 hour maximum
NOx
20
91
512
25
Annual arithmetic mean
*NOTE: Class II areas are areas not listed as Class I areas or nonattainment areas.
The following shows the increments allowed over baseline concentrations in Class
III areas:
Pollutant
Increment
PM-10
Annual arithmetic mean
34
60
24 hour maximum
SO2
Annual arithmetic mean
24 hour maximum
3 hour maximum
NOx
40
182
700
50
Annual arithmetic mean
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