mpared to locations further inland. During the winter months, the Pacific High weakens and
migrates to the south allowing Pacific storms into California. At Pismo Beach, which is approximately
15 miles southeast of DCPP, the average annual rainfall is just over 17 inches, most of which occurs
between October and April (WRCC, 2004).
The DCPP site is within the coastal climate zone, where the oceans influence is significant. The prevail-
ing climate is semi-arid to arid. Low-level temperature inversions (from 1,000 to 2,500 feet) occur fre-
quently over the coastal area. This tends to limit vertical dispersion of pollutants and can lead to increased
concentrations of pollutants inland where prevailing winds carry the air. Prevailing onshore winds in
the area of DCPP are from the northwest, which is the prevailing daytime wind direction for the entire
county. The winds are also greatly influenced by local topography. At night, as the sea breeze dies,
weak drainage winds flow down the coastal mountains and valleys to form a light, easterly land breeze.
Occasional winter storms and offshore flows reverse the sea breezes so that winds flow from the east.
Existing Air Quality
Criteria Air Pollutants. With the assistance of the San Luis Obispo County Air Pollution Control
District (SLOAPCD), the California Air Resources Board (CARB) compiles inventories and projections
of major pollutant emissions and monitors air quality conditions in the region. Air quality conditions
are tracked for both criteria air pollutants and toxic air contaminants.
Criteria air pollutants are a group of pollutants for which regulatory agencies have adopted ambient air
quality standards and region-wide pollution reduction plans. Criteria air pollutants include ozone,
carbon monoxide (CO), nitrogen dioxide (NO
2
), sulfur dioxide (SO
2
), particulate matter, and lead.
Toxic air contaminants (TACs) refer to a category of air pollutants that pose a present or potential
hazard to human health, but which tend to have more localized impacts than criteria air pollutants.
Reactive and volatile organic compounds and gases (VOC) and nitrogen oxides (NOx) are also regu-
lated as criteria pollutants because they are precursors to ozone formation. Certain VOCs may also qualify
as TACs. Two subsets of particulate matter are inhalable particulate matter less than ten microns in
diameter (PM
10
) and fine particulate matter less than 2.5 microns in diameter (PM
2.5
).
Ambient Air Quality. Historically, violations of federal and State ambient air quality standards for
ozone and particulate matter have occurred in San Luis Obispo County. In spite of population growth
and increased motor vehicle miles traveled, substantial progress has been made toward controlling these
pollutants. Although air quality improvements have occurred, violations of ambient air quality standards
for ozone and particulate matter can occur. The frequency of the violations and the current air quality con-
ditions are summarized for ozone, PM
10
, and PM
2.5
in Table D.2-1. Refer to Section D.2.2 for details
on the Applicable Regulations, Plans, and Standards.
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Table D.2-1. Local Ambient Air Quality Monitoring Data

Ozone
Ozone
Ozone
PM
10
PM
10
PM
10
PM
2.5
PM
2.5

Monitoring Locations
Year
Days Over
1-hr State
Standard
Max
1-hr
(ppm)
Max
8-hr
(ppm)
Days Over
24-hr State
Standard
Max
24-hr
(�g/m
3
)
Annual
Average
(�g/m
3
)
Max
24-hr
(�g/m
3
)
Annual
Average
(�g/m
3
)
1999 0 0.086
0.069 0 42.0 17.0 20.0
8.2
2000 0 0.068
0.057 0 44.0 19.0 28.2
N/A
2001 0 0.067
0.061 0 39.0 18.7 25.5
N/A
2002
0 0.067
0.058 0 44.0 17.3 20.1
N/A
San Luis Obispo County
2003 0 0.074
0.062 1 59.0 17.3 21.8
7.5
Source: Air Quality Data Website (CARB, 2004a).
Notes: State Standard: California Ambient Air Quality Standard (CAAQS)

ppm: parts per million

�g/m3: micrograms per cubic meter; days over PM
10
CAAQS is calculated based on monitoring every sixth day.

Station Locations: Grover City data for ozone and San Luis Obispo data for particulate matter.
Existing Emission Inventory
Emission sources in San Luis Obispo County are dominated by mobile sources, including on-highway motor
vehicles, railroad locomotives, and marine vessels. CARB compiles regionwide emission inventories that
include planning and forecast estimates for all groups of sources. The existing inventory shows that nearly
50 percent of all NOx emissions in the region are from on-road motor vehicles, and more than 10 per-
cent of NOx emissions in the county are from construction-type equipment. Dust from construction activity
in the county accounts for more than 10 percent of all PM
10
. Relatively minor stationary sources are in
use at DCPP for supporting routine operation of the power plant. The daily emissions from electric
utilities, dust from construction activity, off-road equipment used during construction, ships, and all on-
road motor vehicles are shown for inventory year 2003 in Table D.2-2.

Table D.2-2. Daily Emissions within San Luis Obispo County (2003)
NOx
VOC
PM
10

CO SOx
Source
Category
(ton/day) (ton/day) (ton/day) (ton/day) (ton/day)
San Luis Obispo County totals
26.47
28.38
32.42
170.67
10.90
Source Category Subtotals





Electric
utilities
/
cogeneration
0.89 0.11 0.15 2.67 0.01
Construction and demolition dust ---
---
4.06
---
---
Off-road equipment
(all construction and mining)
2.57 0.31 0.18 1.83 0.01
Ships and commercial boats
(all vessels)
1.26 0.08 0.10 0.24 0.18
On-road motor vehicles
(all on-road vehicles)
12.28 7.89 0.33 75.58 0.08
Source: 2003 estimated source category emissions from Almanac Emissions Data (CARB, 2004b). DCPP Steam Generator Replacement Project
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Draft EIR
D.2.2 Applicable Regulations, Plans, and Standards
Ambient Air Quality Standards
Air quality is determined by measur-
ing ambient concentrations of crite-
ria pollutants, which are air pollutants
for which acceptable levels of expo-
sure can be determined and for which
standards have been set. The degree
of air quality degradation is then com-
pared to the current National and Cal-
ifornia Ambient Air Quality Stand-
ards (NAAQS and CAAQS). In gen-
eral, the CAAQS are more stringent
than the corresponding NAAQS. The
standards currently in effect in Cali-
fornia are shown in Table D.2-3.
Air quality standards are designed to
protect those people most susceptible
to respiratory distress, such as as-
thmatics, the elderly, very young chil-
dren, people already weakened by
other disease or illness, and people en-
gaged in strenuous work or exercise.
Attainment Status
Geographic areas are designated by either the U.S. Environmental Protection Agency (USEPA) or CARB
as a nonattainment area if violations of the ambient air quality standards are persistent. San Luis Obispo
County is classified as a moderate nonattainment area for the State ozone standard, and like many areas
in the State of California, it is a nonattainment area with respect to the PM
10
CAAQS. The area is des-
ignated as an attainment area for all other standards. A summary of the air quality status relative to the
standards is provided in Table D.2-4.

Table D.2-4. Attainment Status of San Luis Obispo County
Ozone Particulate
Matter
CO NO
2
SO
2

Air Basin
State Federal State Federal
State
Federal State Federal State Federal
San Luis
Obispo
Moderate
Nonattainment
1-hr: A
8-hr: A
PM
10
: N
PM
2.5
: A
PM
10
: A
PM
2.5
: A
A A A A A A
Note:
A: Attains Ambient Air Quality Standards; N: Nonattainment.
Source: CARB,
2004c and USEPA, 2004.
Table D.2-3. National and California Ambient Air Quality Standards
Pollutant
Averaging
Time
California
Standards
National
Standards
1-hour
0.09 ppm
0.12 ppm
Ozone
(O
3
)
8-hour
0.08
ppm
24-hour 50
�g/m
3
150
�g/m
3

Respirable particulate matter
(PM
10
)
Annual mean
20 �g/m
3
50
�g/m
3

24-hour
65
�g/m
3

Fine particulate matter
(PM
2.5
)
Annual mean
12 �g/m
3
15
�g/m
3

1-hour
20 ppm
35 pm
Carbon monoxide
(CO)
8-hour
9.0 ppm
9.0 ppm
1-hour 0.25
ppm
Nitrogen dioxide
(NO
2
)
Annual mean

0.053 ppm
1-hour 0.25
ppm
24-hour
0.04 ppm
0.14 ppm
Sulfur dioxide
(SO
2
)
Annual mean

0.03 ppm
Notes: ppm: parts per million; �g/m3: micrograms per cubic meter; : no standard
Source: CARB Ambient Air Quality Standards Table, 2003. DCPP Steam Generator Replacement Project
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Air Quality Plans and Regulations
The federal Clean Air Act, as amended, and the California Clean Air Act both require that air quality
management plans be formulated demonstrating how the ambient air quality standards will be achieved
in nonattainment areas. These laws also provide the basis for the implementing agencies to develop mobile
and stationary source performance standards.
The SLOAPCD is the primary agency responsible for planning, implementing, and enforcing federal and
State ambient standards within the County. In order to demonstrate how the area will eventually meet
the standards, the SLOAPCD maintains the regional Clean Air Plan, most recently revised in 2001.
The Clean Air Plan is a compilation of measures and regulations that govern how the region will man-
age ozone precursors (NOx and volatile organic compounds or VOCs) to eventually attain and maintain