Ohio EPA No Longer Accepting SCREEN3 Modeling

According to Ohio EPA’s Air Quality Modeling Webpage, effective April 1, 2020 Ohio EPA will no longer accept SCREEN3 results for “state-only” air quality modeling. Facilities must use AERSCREEN or AERMOD for future “state-only” air quality modeling. Ohio EPA is in the process of updating Engineering Guide No 69 (EG 69) to reflect this and other changes. This is great news for consultants and not so great news for industry.

EG 69 is Ohio EPA’s primary guidance on conducting air quality modeling and is written in a question and answer type format. EG 69 was first issued in 2003 and was updated in 2014 and 2018. GT played a significant role in the 2014 and 2018 versions of EG 69, especially maintaining the ability to continue to use SCREEN3 for “state-only” air quality modeling and the improvements to Table 3 – Modeling Standards and Screening Levels.

According to Footnote 1 of EG 69, “This Engineering Guide is not binding, does not have the force of law, is not a “rule” as defined in section 119.01(C) of the Revised Code, and is not a “policy” as defined in section 3745.30(A)(1) of the Revised Code.” So, if EG 69 is not a law, rule, or policy, then what is it? Well, it is Ohio EPA’s non-binding guidance on air quality modeling for “state-only” and federally enforceable modeling projects. If you follow EG 69 to the “T” then your modeling project will more than likely be accepted by Ohio EPA, and if you deviate from it in any significant way, then you take the chance of having your modeling project rejected and the issuance of your permit delayed. If you deviate from EG 69, you also expose your modeling project and resulting permit to lawsuits from US EPA and environmental groups. Ohio EPA does not want EG 69 to have the force of law, rule, or policy because they want the flexibility to allow facilities to deviate from it from time to time without EG 69 becoming the basis for courts overturning permitting decisions made by Ohio EPA.

SCREEN3 and AERSCREEN are both screening models, meaning they are a simplified version of their parent model. ISC3 was released in the early 1990s and is the basis for SCREEN3, which was released in 1995 and most recently updated in 2013. AERMOD replaced ISC3 as the preferred air dispersion model by US EPA in November 2005 and is the basis for AERSCREEN. Both SCREEN3 and AERSCREEN can only model single sources and typically produce higher offsite concentrations than their parent models. Both ISC3 and SCREEN3 are no longer supported by US EPA but can still be found on US EPA’s SCRAM[1] website.

The DOS versions of both SCREEN3 and AERSCREEN can be downloaded for free from US EPA’s SCRAM website. Both SCREEN3 and AERSCREEN are also available within a Graphical User Interface (GUI) environment from several different consulting companies with an annual license subscription. A GUI isn’t really necessary for running SCREEN3, but greatly simplifies data input and model setup for AERSCREEN. Even for the experienced modeler, GT highly recommends the use of a GUI when running AERSCREEN or AERMOD. The table at the end of this article compares the input parameters for SCREEN3 and AERSCREEN. As you can see, SCREEN3 requires very little information to run, while AERSCREEN may require significantly more information, especially if the regulatory agencies require the inclusion of terrain data. The SCREEN3 user guide is 68 pages long and the AERSCREEN user guide is 115 pages long. SCREEN3 does not rely on any other programs to run successfully. AERSCREEN requires the user to download AERSCREEN, AERMOD, and MAKEMET executables from US EPA’s SCRAM website, and the AERMAP and/or BPIPPRM executables are required if terrain files and/or complex buildings inputs are used.

GT believes Ohio EPA will need to include a lot of additional AERSCREEN guidance in EG 69. For example, is terrain data required; when is BPIPPRM required; what min. and max. ambient temperatures should be used; what min. wind speed should be used; what land use type should be used; what surface roughness length should be used; what Albedo value should be used; and what Bowen Ratio should be used? Perhaps Ohio EPA will have to provide this information on a county-by-county basis.

GT believes most environmental managers will have great difficulty running AERSCREEN and as a result will be forced to rely on consultants to run this model. Even some consultants who have not invested in a GUI will be hard pressed to run AERSCREEN cost effectively.

Prior to April 1, 2020, GT’s standard approach was to use SCREEN3 for “state-only” modeling projects involving a single release point or even in some circumstances, projects involving multiple release points. If the SCREEN3 results exceeded the regulatory thresholds, then GT would jump straight to AERMOD. The main difference between AERMOD and AERSCREEN is that AERMOD requires the user to obtain meteorological data and terrain data, while meteorological data is not required, and terrain data is optional in AERSCREEN. Ohio EPA provides AERMET output files for all counties in Ohio, which significantly narrows the gap between AERSCREEN and AERMOD, and obtaining the terrain data is not that difficult if you know where to go and you are using a GUI. For Ohio projects, GT will likely use AERMOD exclusively. For projects outside of Ohio, we may use AERSCREEN if the state agency does not provide AERMET output files like Ohio. So, this means facilities will likely rely on consultants for more of their air quality modeling needs and will likely pay more for the air quality modeling.

GT routinely conducts air quality modeling for sophisticated Prevention of Significant Deterioration (PSD) major new source review permitting projects as well as for minor source permitting projects requiring modeling for air toxics and criteria pollutants.

Please contact Ron Hansen, Owner/Principal Consultant at (614) 794-3570 Ext 121 or rhansen@gtenvironmental.com for more information.