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It’s a Cluster#$%&…Top Challenges Facing Facilities Subject to SO2 Data Requirements Rule

Posted: September 10th, 2015

Authors: Colin M. 

For a while now ALL4 has been writing about the Sulfur Dioxide (SO2) Data Requirements Rule (DRR), including our most recent update on the final SO2 DRR. For those who are new to the process, the SO2 DRR is the U.S. EPA rule that outlines how State agencies should assess attainment or nonattainment with respect to the 1-hour SO2 National Ambient Air Quality Standard (NAAQS) (for areas that don’t currently have existing State run SO2 ambient monitors) and which facilities need to be directly evaluated as part of the process through either air dispersion modeling or through the installation of new ambient SO2 monitors.  Facilities which emit more than 2,000 tons per year of actual SO2 emissions have three (3) options to demonstrate attainment with the NAAQS:

  1. Conduct air dispersion modeling to show modeled attainment with the 1-hour SO2 NAAQS based on three (3) calendar years of actual emissions; or
  2. Install an ambient monitor or monitors to measure ambient SO2 concentrations for a period of three (3) years.  Often times dispersion modeling will still be used to identify areas of maximum modeled concentrations and therefore where an ambient monitor would be installed.
  3. Take a federally enforceable permit limit to limit facility-wide SO2 emissions to less than 2,000 TPY of SO2.

Facilities should be taking the following actions to evaluate the attainment status and corresponding attainment option for the SO2 DRR:

  1. Begin preliminary discussions with State agencies about their overall approach to the DRR including what role the agency will play in the DRR evaluation process and what information they will expect from your facility.
  2. Gather hour by hour fuel usage, production data, emissions information, and flow rates for the three (3) most recent calendar years of operation for use in air dispersion modeling.
  3. Conduct preliminary air dispersion modeling as outlined in U.S. EPA’s Air Dispersion Modeling Technical Assistance Document (TAD) referenced in the final DRR.

Evaluate SO2 compliance options (i.e., dispersion modeling versus ambient monitoring) from a capital/logistical standpoint.  Note: The sooner facilities start to evaluate their compliance options and engage State agencies, the better.  Decisions about the compliance options need to be made by July 1, 2016 with many State agencies require specific plans for monitoring or modeling in advance of that date.

The reality is that even with a final rule having been issued, there are still a cluster of unknowns related to the rule which can make it increasingly challenging for facilities to navigate a compliance approach.  To complicate the matter, State agencies are in the same position in trying to interpret what will be acceptable to U.S. EPA when NAAQS designation recommendations are submitted.  At ALL4, we have been assisting a number of clients with the SO2 DRR over the last few months and have identified the top challenges facing facilities subject to the SO2 DRR.

1. State agencies are approaching the SO2 DRR differently.

Not all State agencies are taking the same approach in evaluating applicable facilities with respect to SO2 DRR requirements.  Some State agencies are taking a hands on approach with facilities reaching out to facility contacts, scheduling meetings, establishing deadlines, and requesting the results of each step of the process.  Other State agencies are taking the opposite approach, putting the onus on the facilities to figure out for themselves the best approach to take and serving in a review capacity only.  The bottom line is facilities need to be in contact with State agencies to know how they plan to address the SO2 DRR because the approach of an individual State agency will likely impact the way that dispersion modeling is conducted, the decisions on location and number of ambient monitors to be installed, and the information that needs to be presented in the final analysis.

2. Clusters of SO2 emitting facilities could be drug into the SO2 DRR as well.

So you emit less than 2,000 tons per year (tpy) of SO2?  Perfect, the SO2 DRR doesn’t apply to you, right?  Not so fast.  In U.S. EPA’s final SO2 DRR preamble, clusters of SO2 emitting facilities are specifically addressed.  U.S. EPA states that clusters of SO2 sources that as a whole may have impacts similar to singles sources that emit greater than 2,000 tpy, will be evaluated on a case-by-case basis.  Many commenters suggested that U.S. EPA outline specific criteria for evaluating the scenario of clustered sources, but in the final rule U.S. EPA stated only that no specific criteria would be outlined due to the complex number of variables that could impact the significance of these smaller sources.  Sources that emit less than 2,000 tpy should take a hard look at surrounding facilities to determine if they are potentially impacted and start having some preliminary discussions with their State agency.  The last thing you want is to be blindsided that you will be impacted by the SO2 DRR.

3. Going down the monitoring route?  Cost may not be good enough justification for siting an ambient monitor.

If you are planning to install an ambient monitor, chances are you are taking a hard look at the cost associated with procuring the ambient monitoring equipment, accessing the potential monitor site, providing the potential monitor site with electricity, and clearing trees and vegetation to meet monitoring siting requirements and for the access road and potential monitor site itself.  In an ideal world, the location for a monitor is one that requires little capital expense and effort to access.  Of course, this is the real world and the chances are slim that the modeling you are conducting to site your ambient monitor actually works out that way.  In fact, you probably have numerous locations with similarly elevated modeled concentrations relative to other locations.  But be warned, if the model results show that one location clearly has the most significant impact, you may have a hard time arguing that accessing that location is reason enough to exclude that location.  ALL4 has received direct feedback from State agencies that cost is not a sufficient justification to exclude a potential ambient monitor site, especially if it is clearly the location of maximum modeled concentrations.  It is important to identify these possible issues early in the process and evaluate options for other possible monitoring locations.

4. Is one (1) ambient monitor good enough?

This is really “the” question if you choose to go down the ambient monitoring route.  U.S. EPA has made it very clear that at least one (1) ambient monitor must be installed for those facilities electing to utilize ambient monitoring to demonstrate attainment.  U.S. EPA’s example siting an ambient monitoring in the U.S. EPA Monitoring TAD shows one location that is far and away the best location to install an ambient monitor.  The reality is that the modeling results do not always work out cleanly.  Many times, one (1) location isn’t clearly the best choice; there is a large gray area.  In fact, we have seen instances where the worst case impacts are similar and occur on opposite sides of the facility property.  While there are certain arguments to be made justifying the installation of one (1) ambient monitor, facilities need to prepare for the reality that U.S. EPA and State agencies could require multiple ambient monitors and be prepared to counter those requests.  The primary question to ask: ”If I’m installing one (1) ambient monitor, is it protective of the possible concentrations in other locations?”  The answer could be yes and you should be prepared to present that justification for your specific situation.

5. On-site meteorological data is great for Prevention of Significant Deterioration (PSD) modeling, but maybe not for SO2 DRR modeling.

The U.S. EPA Modeling TAD outlines a specific approach for modeling to show compliance with the SO2 NAAQS.  It states that the meteorological data used for modeling should align with the hourly emissions data.  The Modeling TAD also allows for the use of on-site meteorological data if it is available.  But if the on-site meteorological data is historical and does note align with the most recent three (3) years of hourly actual emissions data, ALL4 has recently received feedback that in this scenario the allowable emissions rate should be used in the modeling as opposed to the actual emissions rates.  This certainly hinders the abilities of facilities to model and show compliance with the NAAQS.  Another potential option might be the use of U.S. EPA’s recently proposed (as a part of proposed revisions to 40 CFR Part 51 Appendix W, Guideline on Air Quality Models) Mesoscale Model Interface (MMIF) Program which could be utilized to develop a site specific meteorological dataset for the three (3) most recent years.  Again, this highlights the importance of engaging your State agency early in this process.

6. Hourly fuel usage and production data can be painful to reconcile.

The Modeling TAD states that actual hourly emissions data should be used to conduct modeling which means it’s time to roll up your sleeves and get into the weeds of your data.  Three (3) years of hourly data is a lot of data and now let’s assume you need that information for several SO2 emissions sources.  The amount of data that you need to sort through adds up quickly.  Trying to reconcile hourly fuel usage and production data with process downtime and other process codes is tedious work.  I cannot emphasis enough how this task, specifically, seems to be where much of our effort has focused on with our recent SO2 DRR projects.

All of this heightens the importance of working through issues early.  If you haven’t started evaluating the SO2 DRR and you emit 2,000 tpy of SO2, now is the time to get started.  There are numerous issues to work through before the July 1, 2016 deadlines for submitting dispersion modeling protocols or ambient monitoring plans.  It’s important to start opening the lines of communication with State agencies and U.S. EPA early in the process.  If you can get State agency and U.S. EPA involvement well before the deadlines next year, you can help to minimize the impacts of any surprises.  The last thing anyone wants is to find out two (2) ambient monitors will be required at the 11th hour.

ALL4 is available to assist with any and all aspects of the SO2 DRR.  Contact Colin McCall (cmccall@all4inc.com) at (678) 460-0324 ext. 206 or Chuck Doyno (cdoyno@all4inc.com) at (678) 460-0324 ext. 204 for more information about the ways that we can assist with the SO2 DRR and the SO2 NAAQS implementation process.


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