Cooper Environmental

Guide for developing a multi-metals, Fence-line monitoring plan for fugitive emissions using x-ray based Monitorsa case study


Airborne metals and metal compounds are of particular concern to human health. Not only are they included in the United States (U.S.) Environmental Protection Agency’s (EPA) list of 187 hazardous air pollutants (HAPs), they represent 8 of the 33 urban pollutants identified by the EPA as posing the greatest potential health threat in urban areas. This is particularly significant since 80% of the U.S. population resides in urban areas. Premature deaths linked to particulate matter (PM), particularly PM in the respirable range, have been shown to be comparable to deaths from traffic accidents and second-hand smoke. Contemporary researchers in the field of airborne metals’ health effects are finding that the metals components of PM are particularly toxic and cause a multitude of significant health effects from pulmonary inflammation, to increased heart rate variability, to decreased immune response. These effects are not only seen from chronic exposure, but also from short-term acute concentration spikes in ambient air.

A significant portion of the U.S. population lives in the vicinity of metals sources, such as waste incinerators, metal processors, metal fabricators, welding facilities, etc., where they may be exposed to airborne metals greatly in excess of typical ambient concentrations. With modern regulatory limits and controls on stack emissions at industrial facilities, many of the major regulatory and technological issues surrounding stack fumigation and pollution have been resolved. Alternately, fugitive emissions, also described as uncontrolled process emissions, occur at or near local elevations and can dominate local hazardous air pollutant exposure. In fact, recent modeling at secondary lead smelters indicates that at many facilities the majority of daily emissions are fugitive in nature. Additionally, at facilities such as primary and secondary lead smelters, short-term lead concentration spikes may comprise the majority of the mass of lead emissions and subsequent human exposure for a given month. Fugitive emissions typically occur intermittently and unpredictably throughout the course of a plant's daily operations. In addition, fugitive emission transport and exposure to human receptors may depend upon specific meteorological conditions, wind direction, and facility operations. Because these emissions are not measured by typical stack monitors, the specific source of the emission can be difficult to identify and control.

The objectives for a regulatory approach are to protect human health through continued reduction of hazardous air pollutant (HAP) exposure by measuring short-term peaks in concentration, identifying and apportioning sources, and providing feedback to plant operators. Historically, plant operators and regulators have not had the capability to measure short-term ambient metals concentrations, which is necessary to characterize the potential for acute exposure health effects and fulfill regulatory criteria. Commonly used ambient metals sampling devices generally collect 24-hour integrated average samples, which are then sent off to be analyzed in a lab, and as a result sampling data may take weeks to process. In addition, 24-hour average concentration samples do not fully account for shifts in the environment, such as short-term ambient metals spikes related to local fugitive emissions. In fact, during a short-term metals exposure event, 24-hour average sample concentrations for metals like arsenic and lead may be orders of magnitude lower than the 4-hour or 15-minute average concentration from the same day. To achieve an accurate characterization of daily exposure, continuous monitoring is essential. Without the capacity to correctly characterize short-term exposure on a real-time scale, it has been difficult or impossible to either identify the source of the emission or to develop regulatory control strategies to reduce the impact of acute, high concentration exposures.

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