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Agenda SO2 Data Requirements Rule (DRR) Overview Process to Characterize Ambient Air Quality

• Air Dispersion Modeling • Ambient Air Monitoring• Technical Assistance Documents (TADs)

Implications of Upcoming Modeling and Regulatory Policies• Proposed Appendix W changes

Case Study Questions and Open Discussions

SO2 DRR Overview:Who and When?


Final rule issued August 11, 2015 (40 CFR Part 51, Subpart BB)

Applies to facilities that:1. Emitted 2,000 tons per year (tpy) of actual

emissions during most recent calendar year2. Not located in a nonattainment area3. Discretion to include additional sources

Affected facilities will model or conduct monitoring to characterize ambient air

Who is Subject?


Agencies notify U.S. EPA regional offices on list of SO2 sources by January 15, 2016

Agencies specify whether each source will use monitoring or modeling by July 1, 2016

Air dispersion modeling protocols due by July 1, 2016; analysis due January 13, 2017

Ambient monitoring plans are due by July 1, 2016; monitors operational by January 1, 2017

NOW is the time to react!

When is This Happening?

SO2 DRR How: Air Dispersion Modeling


SO2 Modeling TAD Representative

meteorological data for most recent 3 years

Receptors placed only where an ambient monitor could actually be located

Comparison to Regulatory Modeling

Regulatory Modeling Representative

meteorological data for 5 years

Receptors placed anywhere deemed as ambient air

Rule of Thumb: Maximum ground-level concentration at a distance approximately 10 times stack height in flat terrain


Traditional PSD Receptor Grid


DRR Receptor Grid


SO2 Modeling TAD Actual emission rates

from past 3 years Characteristics can be

varied on an hourly basis

Use of actual (i.e., current) stack heights only

Comparison to Regulatory Modeling

Regulatory Modeling Potential to emit Can vary emissions

rates – but typically not varied hourly (and could result in permit limits)

Use of GEP, not current stack height


Varying emissions data is intensive and time consuming

Intermittent sources (i.e., emergency generators) only evaluated if operated enough to contribute to 99th percentile

Actual emissions can be an improvement over allowable emissions

June – December 2013: 246 monitors across the U.S. did not collect 1-minute meteorological data due to a lack of funding.

Considerations for DRR Modeled Emission Rates


Pros: • Less costly • Can be less time consuming

Cons: • Determining actual emissions can be challenging • Ongoing compliance demonstrations built into the rule• Facility may not be able to demonstrate compliance

with the NAAQS

Pros and Cons of Modeling

Ambient Monitoring for SO2 DRR


A facility may use a combination of the following:1. Perform dispersion modeling to identify location(s)

of maximum SO2 concentrations• Normalized emissions rate• Rank each receptor for concentration and number of days

when that receptor is the highest for the day for all receptors

2. Install temporary ambient monitors at several locations to identify the location(s) of maximum SO2 concentrations

Steps to Determining Ambient Monitoring Locations


Pros: • More realistic view of ambient SO2 emissions• Future compliance requirements may diminish

Cons: • Capital costs (installation and upkeep) • Time consuming• Noncompliance could mean ongoing monitoring

obligations and more stringent future air permitting obligations

Pros and Cons of Monitoring

Implications of Upcoming Policies


Constant maximum emission rate overly conservative• Compounded by combining with observed

monitoring concentrations as background Higher concentrations during periods of SSM

• May 22, 2015 SIP call rule Emission Variability Processor (EMVAP)

• Incorporate varying emissions with Monte Carlo statistical technique; 50th percentile monitored concentration as background

Appendix W proposed changes

Importance of Variable Emissions


What 1-hour background concentration do you add to modeled concentration? • Highest hourly modeled concentration paired with

highest hourly monitored concentration• 3-year average of 99th percentile of maximum daily

(p=0.0001; 1 exceedance every 10,000 days!)• EMVAP and 50th percentile background concentration

Probability of exceedance 0.005; equivalent to 99.5th percentile, compared to 99th percentile form of the standard

Selection of Ambient Air

Case Study


Chemical plant in the southeast Modeling not previously conducted CEMS data for largest SO2 emitting source, limited

emissions data for other sources Relatively flat terrain in rural setting Next door neighbor is utility power plant

Background


2 tasks• Modeling-based evaluation

Cumulative concentration of plant’s sources relative to the NAAQS

• Monitoring-based evaluation Rank normalized modeling results

Project


Recommendations for mitigating elevated concentrations• Balance with future expansion plans with facility,

particularly PSD projects If not possible, recommend ambient monitoring

locations Outcome

• Modeling shows concentrations below NAAQS*• Expanded scope to include other criteria pollutants

and PTE rates in anticipation of future modeling needs such as a PSD project

Compliance Approach

Www.all4inc.com | Philadelphia | Atlanta | Houston | Washington DC SO 2 Data Requirements Rule – A...

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