Optimal Strategies for Minimizing the Emissions of Volatileorganics and Odors During Excavation of MGP Sites

MGP sites are typically contaminated with a complex mixture of coal tars, primarily represented by 500 to 3,000 separate polycyclic aromatic hydrocarbons (PAHs) containing two to six benzene rings, phenolics, volatile organics, and inorganic compounds of sulfur and nitrogen. Emissions of volatile compounds during excavation can create odors, and can cause problems meeting short or long term perimeter ambient air quality guidelines or criteria established by the utility or regulatory agencies. Benzene is the hydrocarbon that typically drives public health concerns, but other compounds such as naphthalene are important due to its low odor threshold and increasing regulatory interest. Odor control technologies such as plastic barriers, long-lasting foam, and misting systems are often used to control odors during soil hauling and excavation. Currently, there is no systematic risk-based method for finding the “optimal” emission control strategy during excavation of a MGP site.In this paper, an odor index and Hazard Quotient will be presented, which are calculated using air concentrations of several sentinel compounds, typically emitted during MGP site excavation. The air concentrations are calculated using an air emission model which was developed to model the site excavation process and this model was tested and verified by actual laboratory-scale measurements of air emissions from several contaminated MGP soils. The validated model has been incorporated in an Excel-based program, MGPSEEP, (MGP Site Emissions Estimation Program), which has been field-tested by comparing with actual field-scale measurements during actual excavation of a MGP site. Details of the modeling and experimental approach and its field-scale testing will be presented in this paper.