Comment submitted by H. Hammer

I am an environmental scientist with extensive experience as an environmental consultant, primarily related to air quality analysis and review. It is my opinion that this guidance is unclear, incomplete, and creates a problematic precedent for all microscale air quality analysis of local, state, and federal actions. The guidance states that quantified hot-spot analyses should not be performed until EPA issues guidance and requires quantified analyses. Although this rule applies only to transportation conformity, it is interpreted and applied broadly by agencies as a basis for not allowing any quantified microscale analysis of PM2.5 impacts of projects under NEPA and under state (and possibly city/local) review as well, where a determination of the significance of potential impacts is required, as well as the full public disclosure of potential significant adverse impacts. The rules given for qualitative analysis are incomplete and short on details. The examples given in the rules of comparative determination are limited; they include comparing the project to existing projects and/or actual monitored values. The latter case clearly relies on quantified analysis, which is contradictory to the language stating that only qualitative analyses be performed. The main problems with these examples, and therefore with the entire process are: (1) Most projects are not located immediately adjacent to an air monitor, and if they are, would not necessarily have the same area-wide emissions characteristics. In urban areas, ambient air quality monitors are affected by both region-wide and local emission sources, and a single source's impact cannot usually be detected (monitors are usually designed to avoid source-oriented impacts). Therefore, in almost all cases, an existing project could not be used to estimate a future condition for another location. It should also be noted that local impacts would not necessarily be represented by a distant rooftop monitor; if an existing project has a local impact (e.g. at nearby residential buildings), saying that an existing project did not trigger an exceedance of the NAAQS does not necessarily mean that the future project would not have a local impact--which is what a hot-spot analysis is supposed to identify. (2) Based on the EPA guidance and examples, projects located in areas where the standard is currently exceeded have no means to determine whether the increment in ambient pollutant concentrations would be significant, since they are not allowed any quantification. Similarly, it is not clear on what basis the effectiveness of mitigation is determined without any analysis. (3) The examples only include mobile sources. However, there are projects that fall under transportation conformity which have local impacts from nonroad components, such as intermodal, railway, or other similar impacts. Furthermore, the fact that this rule addresses only transportation conformity is contradictory: general conformity would still require quantified emissions analysis to determine if the project is de minimis or not, and if there is a possibility of local impacts, would also require a hot-spot analysis which may be quantified. Since general conformity projects can include mobile sources, and since transportation projects may include non-road sources, there would be two approaches for assessing the same type of impacts. EPA's effort to identify a screening process in which not every project would need detailed quantified analysis is commendable. However, this is not successfully achieved with the current rules and guidance, and the guidance precludes the option of actually estimating the potential for any impacts. Therefore, an agency relying on this guidance to conclude that a project would have no significant adverse impact on air quality, in most cases which are not obviously so, would be vulnerable to legal challenge; however, should they choose to determine that potential significant adverse impacts are possible, there is no analysis to demonstrate what those might be, where they might occur, and what can effectively be done to mitigate it, thus leaving the project with no solution at all. Quantified analysis based on the existing models and guidance, although imperfect, at least give a consistent basis for estimation of the magnitude of predicted impacts, and basis for comparison with local or state de minimis incremental levels which are currently in use.