Imperial County PM10 SIP:Update

Imperial County APCD

SIP Workgroup Meeting

September 24, 2008

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Agenda

Ambient air quality, NAAQS exceedences, and design value

Emissions inventory and Significant Sources

Attainment demonstration– For potential “but-for” exceedences:

“But-For” attainment demonstration guidance Proposed methodology: the 5 technical approaches and weight-of-evidence determination

– Other exceedences, if any: Attainment and 5% demonstration (including effect of control strategy)

Next Steps

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Exceptional Events Update September 8, 2006 Westmorland – data invalid

due filter sample problem April 12 and June 5, 2007 – comments from EPA

incorporated into revised Exceptional Events documentation, resubmitted to ARB/EPA– “traditional” high-wind events

September 2, 2006 – comments from ARB being incorporated into Exceptional Events documentation

– This is a “Class 3” exceptional event – mesoscale event and thunderstorm activity

– Greater documentation challenges

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Remaining Exceedences

Remaining exceedences are in Calexico– March 11, 2005: 169 g/m3 in Calexico-Grant, very

low wind speeds, strong southerly component

– December 12, 2005: 211 g/m3 at Grant, 188 g/m3 at Ethel, very stagnant conditions, strong southerly component

– December 21, 2006: 171 g/m3 at Grant, very stagnant conditions, strong southerly component

– December 25, 2006: 248 g/m3 at Grant, very stagnant conditions, extremely high PM10 throughout Mexicali

Design value: 248 g/m3 on December 25, 2006– Per discussion with EPA

– All exceedences will be evaluated (see later slides)

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Agenda

Ambient air quality and NAAQS exceedences

Design value

Emissions inventory

Attainment demonstration– For potential “but-for” exceedences:

“But-For” attainment demonstration guidance Proposed methodology: the 5 technical approaches and

weight-of-evidence determination

– Other exceedences, if any: Attainment and 5% demonstration (including effect of

control strategy)

Next Steps

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Inventory Status

ENVIRON has received latest information from IC Public Works on local unpaved roads– relatively small changes the total mileage of roads with ≥

50 ADT and < 50 ADT– Will include information on currently treated road mileage

IID has reviewed canal access and maintenance unpaved road mileage and daily trip information– Minor change from 2005 BACM analysis (being confirmed

for each road type – possible double-counting of American Canal roads, no roads with > 20 ADT)

Inventory for Draft SIP will be finalized after remaining information on unpaved roads is incorporated

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Significant Sources for PM10

Source categories contributing ≥ 5 g/m3 to ambient PM10 concentrations must be controlled by BACM

De Minimis (DM) value is emission threshold in tpd

DM = total emissions ×

Draft Peak County 24-hour DM:– Emissions (tpd): 549 – Ambient (ug/m3): 230– DM (tpd): 11.9

Significant sources (Draft):– Windblown dust (open areas)– Unpaved roads

(entrained and windblown)

5 g/m3

ambient PM10 air concentration

Source Categories PM10 Emissions (tpd)

Significant (≥ DM value)

Windblown Dust from Open Areas 157.35

Unpaved Roads (Entrained and Windblown) 91.99

Windblown−Non-Pasture Agricultural Lands 10.81Farming−Tilling Dust 7.10

De Minimus ≥ 1 tpd

Paved Road Dust 4.19

Industrial Processes 2.79

Cattle Feedlot 2.77

Waste Burning 2.77

Construction 1.95

From the 2005 BACM Analysis(annual controlling DM=5.0 tpd):

May be slightly updated with new EI

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Agenda

Ambient air quality and NAAQS exceedences

Design value

Emissions inventory

Attainment demonstration– For potential “but-for” exceedences:

“But-For” attainment demonstration guidance Proposed methodology: the 5 technical approaches and

weight-of-evidence determination

– Other exceedences, if any: Attainment and 5% demonstration (including effect of

control strategy)

Next Steps

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Attainment Demonstration

Attainment demonstration – Design value: 248 g/m3 at Calexico-Grant– 4 remaining Calexico exceedences in 2005-2007 (assumes

other exceedences are confirmed as Exceptional Events)

EPA attainment demonstration guidance– August 1997 Federal Register, pp. 41998-42017– Includes guidance on Clean Air Act Section 179B (“but-for”)

attainment demonstrations– Includes guidance on Serious Area SIP requirements, including

BACM implementation, and a 5% plan with attainment demonstration

At this time, no ‘but-for’ demonstration has been completed for any Calexico exceedence

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Calexico Exceedences

Documentation to include:– Description of each exceedence– Federal Register “But-For” Approaches– Weight-of-evidence summary for each exceedence

to determine if a specific exceedence is a “But-For” exceedence

Description for each exceedence– Imperial and Mexicali PM10, including spatial plots– Meteorological data– Back trajectories– Wind rose– Any special considerations (e.g., Christmas holiday

activity in Mexicali for certain exceedences)

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“But-For” Attainment Demonstration

USEPA guidance (August 1994 FR) describes 5 ‘example’ approaches to a ‘but-for’ attainment demonstration1. “Evaluate and quantify .. changes in monitored PM10

concentrations [in the U.S., near the border] with predominant wind direction.” Analyze wind speed and direction.

2. “Demonstrate that local U.S. emissions … [do] not cause the NAAQS to be exceeded.” Include analysis of background PM10 levels without Mexico emissions.

3. “Analyze ambient sample filters for specific particles from across the border”

4. “Inventory sources on both sides of the border and compare”

5. “Perform air dispersion and/or receptor modeling to quantify the relative impacts”

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Approach 1 and 2: Overview

PM10Calexico, day i = Yi (impact from US emissions) + Zi (impact from Mexican emissions)

Approach 1 and 2 are designed to determine quantitatively the impact from either Mexican emissions or US emissions for each Calexico exceedence based on statistical analyses described in the next 2 slides– Day-specific concentrations attributable to Mexican

emissions would be subtracted from monitored values and compared to the NAAQS

– Day-specific concentrations attributable solely to US emissions would be compared to the NAAQS

Approach 1 and 2 are complimentary

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Approach 1: Statistical Analysis of Impact of Mexican (Mexicali) Emissions

Statistical analysis using available meteorological data at Calexico stations and PM10 data from Imperial and Mexican monitors– Partition lower-wind PM10 data into meaningful

meteorological (wind speed and direction) “groups”– Analysis quantifies the contribution from Mexico for

each “group”, based on its specific characteristics– Analyze each exceedence based on the

characteristics of its “group”

Analysis quantifies the specific contribution from Mexico for each exceedence, based on day-specific conditions

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Approach 2: Statistical Analysis of the Impact of U.S. Emissions

Goal: Analyze the Imperial County emission inventory distribution and a statistical analysis of non-Calexico and Calexico historical PM10 concentrations to quantify expected Calexico concentrations from US emissions alone

Analysis elements– Spatial distribution of Imperial County emissions– Comparative analysis of non-Calexico stations– Comparative analysis of Calexico stations

Quantitative day-specific analysis of expected PM10 concentrations from US emissions alone

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Approach 3: Analysis of Sample Filters

1992-93 Cross Border Transport Study indicate that 70 to 90% from geological dust, 10-15% vehicle exhaust, others

Fugitive PM10 dust does not typically have “signatures” for specific sources (e.g. unpaved roads, construction sites) or locations (inside or outside of US)

Does not help quantify impact of Mexican emissions

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Approach 4: Emission Inventory Comparison

Previous analysis (2004): Mexicali Calexico

Area (mi2) ~200 ~4

Population >760,000 ~32,500

Emissions* (tons/day)

~260 ~13

Inventory analysis being updated for Mexico and Imperial County

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Approach 5: Modeling Analysis

Previous modeling analysis done in 2001– CALMET/CALPUFF– SCOS (1997) inventory, adjusted– Conservative background concentration– Modeled 4 full years (1992, 1993, 1994, 1999)

Limitations of the 2001 modeling analysis

Implications of 2001 modeling analysis in present ‘but-for’ demonstration– Modeled meteorological conditions cover days of interest– Revised emission inventory for days of interest would be

compared to 2001 modeling inventories– Modeling would indicate if local-only exceedence would be

expected

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“But-For” Attainment Demonstration

Status of analysis of Calexico exceedences – ICAPCD has completed the description of each potential ‘but-

for’ exceedence– ENVIRON has completed an initial analysis for each of the “5

approaches” for each exceedence day– A weight-of-evidence (WOE) summary for each applicable

Calexico exceedence will be prepared– ARB and EPA commenting on the initial exceedence

descriptions and “5-approaches’ analyses– Descriptions and analyses will be revised, per ARB and EPA

comments; WOE summary updated

Draft Chapter 5 (Attainment Demonstration) and Appendix V (Technical Analyses) will be circulated to SIP WG for review and comment for all applicable ‘but-for’ exceedences

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“Traditional” Attainment Demonstration

Any exceedence that is not excluded as an Exceptional Event or does not have a ‘But-For’ attainment demonstration will be subject to a ‘traditional” attainment demonstration analysis

Implement BACM/BACT for all significant sources

Plan to achieve annual reductions in PM10 of no less than 5% based on the most recent inventory, until attainment;– Excess reductions in early years can be carried over to

later years– 5% requirement applies to anthropogenic emissions only

Demonstrate attainment of the NAAQS at the earliest practicable date; and

Adopt contingency measures

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Attainment Analysis

Linear rollback modeling– Project ambient concentrations for future years, based

on projected changes in day-specific emission inventory – Future ambient concentrations:

= background + “historical value” x

Will use modified day-specific analysis– day-specific historical exceedence, if any– Baseline 2005 “day-specific” emission inventory and

background level Technical analysis, if required, will be reviewed

by all three agencies before inclusion in draft PM10 SIP

future year emissionsbaseline year (2005) emissions

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Agenda

Ambient air quality and NAAQS exceedences

Design value

Emissions inventory

Attainment demonstration– For potential “but-for” exceedences:

“But-For” attainment demonstration guidance Proposed methodology: the 5 technical approaches and

weight-of-evidence determination

– Other exceedences, if any: Attainment and 5% demonstration (including effect of

control strategy)

Next Steps

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Next Steps for Release of Draft SIP Finalize event documentation

– 3-agency review and applicable SIP technical appendices

Finalize emission inventory for draft SIP– Future year projections (through 2010)

Complete attainment demonstration (‘but-for’, 5%)– Incorporate agency comments– Circulate Chapter 5 and Appendix V to SIP WG– Finalize documentation for draft PM10 SIP

Finalize conformity analysis– Future year mobile source projects (through 2035)

Release of draft PM10 SIP for comments– SIP Workgroup and then for public review