6-13 Air

RESPONSE 6-13

The EPA has established the National Ambient Air Quality Standards (“NAAQS”), which are the concentrations of criteria pollutants in the ambient air that have been determined through extensive health studies to be safe for human health and the environment, including the most vulnerable of the population, which a margin of safety.  As required by RIDEM, Invenergy has completed an air quality impact analysis to demonstrate that the ambient air impact concentrations resulting from the simultaneous operation of the CREC emission sources, the emission sources at the Algonquin Compressor Station and the emissions sources at Ocean State Power, when combined with existing ambient concentrations, will not cause an exceedance of any NAAQS. 

The methodology used for this analysis and the results are summarized in the Air Dispersion Modeling Report for the project submitted to RIDEM on October 30, 2015.  The analysis was completed using AERMOD, an EPA refined air dispersion model approved for use by RIDEM.  All emission sources were modeled at full operation and at their worst-case emission rate of each pollutant. The model was run at all hourly meteorological conditions that have occurred over the most recent five-year period for which such data is available, in this case 2010-2014.  A polar receptor grid was established out to 50 kilometers with receptors located at 25 meter intervals out to 1 km, at 100 meter intervals out to 2 km, at 200 meter increments out to 5 km, at 500 meter increments out to 10 km, and at 1,000 meter increments out to 50 km.  The model then predicted the maximum ambient air impact concentrations resulting from all sources operating simultaneously, at each hourly meteorological condition and at every receptor location within the receptor grid to determine the maximum predicted total impact concentration for each pollutant and averaging period.

The results of the project’s NAAQS compliance determination were detailed in Table 15 of the report and are summarized below (all values are in micrograms per cubic meter):

As shown above, CREC will not cause an exceedance of the NAAQS at any location beyond its property line, even when operating simultaneously with the emissions sources at the Algonquin Compressor Station and at Ocean State Power.  Note that the results presented above represent the maximum predicted total impact concentration at a single receptor location at a single hourly meteorological condition for each pollutant and averaging period.  The margin of compliance with the NAAQS will be greater at every other receptor location and during every other hourly meteorological condition, providing further assurance that air quality levels in the area surrounding the facility will be at levels which have been deemed safe by the EPA during CREC operation.

RIDEM has established a list of air toxic compounds and the concentration levels of each air toxic which are safe for public health and the environment (Acceptable Ambient Levels or “AALs”) in RIDEM Air Pollution Control Regulation No. 22.  Invenergy was required to apply the results of the air quality impact analysis described above to its emissions of air toxic compounds.  As detailed in Table 16 of the Air Dispersion Modeling Report, the worst-case emission rates of air toxic compounds from the CREC will not cause an exceedance of any RIDEM AAL beyond its property line. (Table 16 is attached as Exhibit 1.) The results presented in Table 16 are for the single receptor location and hourly meteorological condition at which the highest impacts were predicted for each pollutant and averaging period.  The project impact concentrations will be lower than the values presented in Table 16 at every other receptor location and hourly meteorological condition during CREC operation.

RIDEM has also established the “Guidelines for Assessing Health Risks from Proposed Air Pollution Sources.”  Invenergy was required to complete a multi-pathway human health risk assessment for the CREC in accordance with the RIDEM Guideline.  The results of the assessment are detailed in the CREC Health Risk Assessment Report submitted to RIDEM on January 27, 2016.  As detailed in the report, the results of the health risk assessment completed for the CREC project met all of the applicability criteria of the RIDEM Guideline, demonstrating that any short or long term health risks which could be associated with exposure to the all of the pollutants that could be emitted from the project are within the acceptable levels established by RIDEM to be protective of human health.