Unlike any other consulting firm, CPP promotes cutting edge techniques to alleviate excessive conservatism in permit modeling to a reasonable level that still protects public health.
With experience dating back to the inception of the Clean Air Act, our experts do more than run the models. We understand the theory and know where the models work and where they don’t. However, unlike any other consultant in the industry, we have unique tools to overcome the areas where the models don’t work. This difference will save you time and money.
CPP uses verified methods to reduce excess conservatism that lead to highly unrealistic results, while meeting NAAQS requirements and protecting air quality. Some of these techniques include:
- Equivalent Building Dimensions (EBDs) Studies. The effect on plumes caused by wind flowing around nearby building structures is called building downwash. In AERMOD these effects are commonly calculated with BPIP. However, BPIP was developed for a specific range of building dimensions and its accuracy is uncertain outside of this range. As an alternative to BPIP, EBDs can be determined through wind tunnel modeling and used in AERMOD for more accurate results. Another potential benefit from using EBDs instead of BPIP is lower predicted concentrations. This could mean significant savings due to reduced costs in pollution control equipment and shorter stacks. Read more about EBD.
- Emission Variability Processor (EMVAP). Current modeling practices assume that emission units operate at full load every hour of the year. This assumption leads to unrealistic concentrations, especially for units that operate infrequently, at variable loads, or that have infrequent high emissions. EMVAP uses a statistical method to address the variability of emissions in dispersion modeling for more realistic predicted concentrations.
- Background concentrations. NAAQS permit modeling requires the inclusion of background concentrations to the predicted values obtained from AERMOD. Current practices pair the extreme values from representative ambient monitors with the predicted values from AERMOD. This assumes that two extremely unusual events occur at the same time. A more realistic method combines the median monitored value with the predicted concentrations from AERMOD. This is statistically valid and produces more accurate results.
- Haul road & volume source estimates based on site-specific dispersion. Fugitive sources, such as paved and unpaved roads, raw material storage piles, outdoor material processing operations, or agricultural activities, are treated as volume or area sources in modeling evaluations. CPP can develop site-specific dispersion coefficients that, unlike AERMOD, will capture the effects of downwash from local features on such sources. Using these refinements produces AERMOD results that are more accurate and often lower at the fence line. Read more about more accurate haul road and volume source estimates.
- Fugitive dust emissions from aggregate/grain handling, storage piles and exposed areas. CPP provides more accurate wind-driven particulate emissions estimates using on-site testing. This method helps evaluate mitigation strategies since it accounts for local features that reduce wind speed. We can also determine site-specific dispersion coefficients for coke pits and aggregate or grain loading operations. Read more about particulate emissions estimates.
- Enhanced plume rise parameters for single or multiple flares. Using wind tunnel modeling and computational fluid dynamics, CPP provides more accurate, site-specific model input parameters that include plume rise effects for single or multiple flares. Using Fire Dynamics Simulator (FDS) Large Eddy Simulation (LES) is the most appropriate and cost-effective method in these cases. Read more about enhanced plume rise modeling.
- The adjusted friction velocity option in AERMET. This is a beta option that EPA added in AERMET to correct issues with friction velocity under low wind speed hours. According to recent comments from EPA, this option may soon be included as a regulatory (non-default) option in AERMET.
- Good Engineering Practice (GEP) Stack Height. Many believe that GEP stack height is limited to 65m or 2.5 times the height of the building. Not true. Depending on the surroundings and the details of the project, wind tunnel testing can justify heights above the formula or, in some cases, show that the higher stack is not actually needed for compliance.
These methods obtain more realistic concentration estimates that still comply with NAAQS. Using advanced modeling and analysis, CPP helps your project overcome regulatory challenges to meet your project’s deadlines. CPP’s expertise can also save you money by avoiding unnecessary emission controls and excessive stack heights.