Most metalcasters do not have PM2.5 limits now, nor will such limits likely


be established unless the facility is modified or replaced.


six states as nonattainment.States will be required to submit plans for these non-attainment areas in 2018 that must provide for attainment by 2020. EPA projects that most areas will be able to meet the new standards based on implementation of federal rules on power plants and diesel engines and that only a few areas will be required to adopt rules for specific sources such as metalcasting facilities.


6


limits likely be established unless the facility is modified or replaced. Limits may be established through rules promulgated by states to meet air quality standards, but these will be rare for metalcasting sources. Generally PM2.5


limits are estab-


lished through permitting require- ments to either • Limit annual emissions below thresholds that would subject a project to the review under either the Prevention of Signifi- cant Deterioration (PSD) or Non-Attainment New Source Review (NNSR) rules.


• Establish limits as either Best Available Control Technology (BACT) under the PSD rules or Lowest Achievable Emission Rate (LAER) under the NNSR rules. Te most common technology


for meeting these requirements is the use of a highly efficient fabric filter baghouse and the limits would include both filterable and condens- able particulate matter.


38 | MODERN CASTING August 2015


Most metalcasting sources do not have PM2.5 limits now, nor will such


Which metalcasting facilities will be subject to PM2.5


limits? 7


sources trigger PSD or NNSR permit requirements? Te PSD and NNSR permit-


Will new PM2.5


required to meet the technology and air quality impact requirements of these rules. Sources can limit emis- sions from new and modified sources to less than 10 tons/year to avoid being subject to these rules through enforceable permit limits. If subject to the PSD rules, the project would be subject to the BACT technology requirement as well as the require- ment to demonstrate that the project would not result in exceedances of the air quality standards or PSD increments. Te air quality assess- ment requirement may pose the biggest challenge for projects subject to the PSD rules. For new and modi- fied sources in non-attainment areas, the NNSR rules require the use of LAER level controls and for sources to obtain offsets from third parties for any emission increases associated with a proposed project. If a proj- ect is subject to either the PSD or NNSR requirements, the time frame for obtaining a permit can extend from three months to a year or more.


ting rules apply to projects where the increase in emissions from the project is expected to exceed certain thresholds. If a location is already a major source under either of these rules, an emissions increase of only 10 tons/year of PM2.5


would be 8


Why is air modeling for PM2.5


a problem? Under the PSD rules an air


quality model is used to predict the ground level concentrations of PM2.5


associated with the proj- emission


M3


ect. The model required under the PSD rule is the AERMOD model that has undergone several modifications since late 2013. The two basic analyses required are an evaluation to demonstrate that the project will not result in an exceedance of the PSD increment and the project plus background air quality levels plus impacts from other nearby sources in the area do not exceed the NAAQS. The PSD increments for PM2.5


are 9 µg/ 4 µg/M3


for the 24-hour standard and for the annual standard.


Lower increment values are used for sources that may construct near Class I areas, which include a number of National Parks. The “increment assessment” may be the limiting analysis, especially for greenfield metalcasting facilities For modified sources, the limit- ing assessment is more often the NAAQS assessment where the modeled value for the source is added to the background air quality value (from a representative moni- tor) as well as impacts from other significant sources near the project site. Typical background values for the 24-hour standard may range from 23 to 31 µg/M3


, leaving very


little room for new sources of PM2.5 since the standard is 35 µg/M3


. Te


recently lowered annual standard of 12 µg/M3


challenge with background levels at or above 11 µg/M3


may pose an even greater in some areas.


Attainment has not been possible to achieve for a number of projects, which either have been shelved or the facilities are continuing to try to find ways to accommodate the specific modeling challenges. Te air quality assessments car-


under the PSD rules


ried out under the PSD permit rules are governed by EPA modeling guidance, which was most recently updated in May 2014. One change in this guidance is that the eighth high (98th percentile) modeled value for the 24-hour standard is used rather than the first high value, which will make it somewhat easier to show the standard will be protected. Also influencing how the modeling assessments are carried out


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