Formatted Title
Using Atmospheric Dispersion and Advanced Health Risk Modeling as a Mitigation Strategy to Advance Air Pollution Control
Background/Objectives
Changes in land use and zoning, air quality management, and environmental justice directives result in a confluence of conflicting regulatory domains. Redevelopment of former industrial sites by municipalities with surrounding “downzoned” commercial, retail, and multifamily and single-family residential land uses present challenges to environmentally compliant operation of air pollution control and remediation systems. Downzoning of these land uses results in a higher residential population density of sensitive receptors, such as public and private schools, hospitals, and convalescent homes. This presentation will focus on the use of regulatorily accepted dispersion modeling, namely AERMOD, as a method for developing mitigation strategies to balance public health and environmental justice concerns with corporate manufacturing, pollution control and remedial responsibilities. AERMOD can be used to address a spectrum of air regulatory rules from subjective odor and nuisance control to management of air toxics health risks associated with operation of air pollution control systems.
Approach/Activities
Presented herein are examples in which advanced modeling was performed using the air regulatory agency modeling guidance for AERMOD, utilizing 3rd-party AERMOD software. The two scenarios are: (1) modeling treated odor concentration of hydrogen sulfide (H2S) from an on-site anerobic wastewater treatment system utilizing reactive carbon adsorption for odor control, and (2) AERMOD coupled with advanced health risk assessments (HRA) to evaluate toxic pollutant health risk for a remediation system to mitigate off-site vapor intrusion and remediation of impacted soils. A suite of over 25 volatile and toxic organic and chlorinated constituents were modeled, including hydrochloric acid, which is an air toxic byproduct of the combustion of chlorinated compounds.
Results/Lessons Learned
Scenario 1: While the regulatory agency took what amounted to a “de minimis approach,” establishing the emission condition for the air permit as an ambient air quality standard (AAQS) for H2S odor and nuisance control, a mass-based numerical limit was established for compliance and in accordance with corporate sustainability directives. This mass-based H2S limit was then evaluated using AERMOD to show that H2S concentrations at the fence line perimeter of the property and within the surrounding residential and commercial land uses were below the AAQS. AERMOD output provided graphical interpretation of the H2S concentration contours and grid concentrations surrounding the facility. The latter is especially important because H2S odor thresholds remain subjective without a numerical threshold established in scientific literature.
Scenario 2: The project required control of an off-site vapor intrusion plume and remediation of the contaminated soils. AERMOD and advanced HRA were utilized to determine the maximum rate at which the remediation system could operate to control the offsite vapor intrusion and remediate the contaminated soils. A more rigorous HRA was also necessitated due to the presence of residential homes and a regional hospital within 1,000 feet of the outer boundary of the site. AERMOD output provided graphical interpretation showing the 1st Highest 1-Hour Values which were used to demonstrate to the air regulator that maximum individual cancer risk (MICR), as calculated according to risk assessment Tier III procedures, would not be exceeded, and public health and environmental justice goals were achieved. A lower tier HRA would have prolonged clean up and exacerbated vapor intrusion risk.