ARCHIVED REPORTS LEC APPLICATION FOR CERTIFICATION

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5.1 AIR QUALITY Preconstruction Monitoring To ensure that the impacts from the LEC will not cause or contribute to a violation of an ambient air quality standard or an exceedance of a PSD increment,an analysis of the existing air quality in the project area is necessary. If a source is subject to PSD review,PSD regulations generally require preconstruction ambient air quality monitoring data for the purposes of establishing background pollutant concentrations in the impact area (40 CFR 52.21(m)). However,a facility may be exempted from this requirement if the predicted air quality impacts of the facility do not exceed the de minimis levels. Modeled impacts from the LEC are compared with the de minimis levels in Table 5.1-39. Since modeled impacts are below the de minimis levels,the project may be exempted from the requirement. TABLE 5.1-39 PSD Preconstruction Monitoring Exemption Levels Maximum Modeled Exceed Monitoring Pollutant Averaging Period Concentration De minimis Level Threshold? NO2 annual 0.26 Ng/m3 14 Pg/m3 No CO 8-hour average 111 Ng/m3 575 tag/m3 No The purpose of the preconstruction monitoring requirement is to verify that background concentrations are adequately characterized to ensure that the national ambient air quality standards are protected.With EPA's approval, a facility may rely on air quality monitoring data collected at District monitoring stations to satisfy the requirement for preconstruction monitoring. In such a case, in accordance with Section 2.4 of the EPA PSD guideline,the last 3 years of ambient monitoring data may be used if they are representative of the area's air quality where the maximum impacts occur due to the proposed source. The background data need not be collected on site,as long as the data are representative of the air quality in the subject area (40 CFR 51,Appendix W,Section 9.2). Three criteria are applied in determining whether the background data are representative: (1) location, (2) data quality,and (3) data currentness.29 These criteria are defined as follows: Location:The measured data must be representative of the areas where the maximum concentration occurs for the proposed stationary source,existing sources, and a combination of the proposed and existing sources. Data quality:Data must be collected and equipment must be operated in accordance with the requirements of 40 CFR Part 58,Appendices A and B,and PSD monitoring guidance. Currentness:The data are current if they have been collected within the preceding 3 years and they are representative of existing conditions. All of the data used in this analysis meet the requirements of Appendices A and B of 40 CFR Part 58, and thus all meet the criterion for data quality. All of the data have been collected within the preceding 3 years, and thus all meet the criterion for currentness.The location and overall representativeness of the data are discussed further below. 29 Ambient Monitoring Guidelines for Prevention of Significant Deterioration(PSD), EPA, 1987. SAC/371322/082410013(LEC_5.1_AIR_QUALITY.DOC) 5.1-59