TRC worked closely with GNPD, state and federal agencies, including EPA and the National Park Service, to develop a permit application and supporting studies for a proposed 600 MW CFB mine-mouth power plant to be located in Stark County, ND, approximately 20 kilometers from Theodore Roosevelt National Park (TRNP) – South Unit, a mandatory Federal Class I Area. The challenges faced by the project, in addition to the typical New Source Review, Prevention of Significant Deterioration (PSD) permitting requirements, included requirements to address impacts on Air Quality Related Values, such as sulfur and nitrogen deposition and visibility impacts within the near-field and far-field observer locations within the closest Class I areas. The near-field visibility analyses required the evaluation of potential impacts on visibility due to plume impairment from the project emissions, a demonstration which had rarely been previously attempted for a major source with substantial emissions from a variety of mining sources and power plant sources at the relatively close proximity to a Class I area. Also, due to the proximity of the emission sources to the Class I area, predicted impacts of certain criteria pollutants were determined to be significant at Class I receptors, thus multisource PSD increment analyses needed to be performed.
TRC’s solutions to the challenges presented by the project location and project specific requirements were rooted in a commitment to work together with the permitting agencies, e.g., EPA and NDDH, and the federal land managers for TRNP to identify and resolve technical issues related to modeling of predicted impacts and refine many of the overly conservative assumptions inherent in then prevailing accepted modeling guidance. TRC modeling staff had previously performed a similar evaluation of the model codes of the approved models, including the recommended plume impairment model PLUVUE II, and had developed alternative application recommendations and appropriate model code in the form of postprocessors to address the limiting factors in the modeling analyses. TRC staff, with the assistance of a developer of the original visibility modeling algorithms and methodology, undertook an experiment to further refine the applicability of the visible plume perceptibility thresholds parameters and developed revised thresholds based on plume subtended angles to an observer. The resulting model enhancements and new model application guidance were presented to the National Park Service staff and subsequently in a modeling protocol that was approved by the EPA, FLMs and NDDH permitting staff.
Although the initially proposed project has been modified several times, including consideration of a conversion to a coal gasification project, in response to recent economic, political and environmental pressures the technical basis established for the permitting of the associated emission sources is solid and can be relied upon to support any project air quality and air quality related values permitting challenges for this site. Collateral benefits of the project have been additional advancements in modeling technology, especially for plume impairment analyses, and guidance for modeling major sources in the vicinity of sensitive protected Class I areas that have been recognized by permitting agencies and FLMs and have been successfully applied on other projects.