Society For Risk Analysis Annual Meeting 2012

Advancing Analysis

Session Schedule & Abstracts

* Disclaimer: All presentations represent the views of the authors, and not the organizations that support their research. Please apply the standard disclaimer that any opinions, findings, and conclusions or recommendations in abstracts, posters, and presentations at the meeting are those of the authors and do not necessarily reflect the views of any other organization or agency. Meeting attendees and authors should be aware that this disclaimer is intended to apply to all abstracts contained in this document. Authors who wish to emphasize this disclaimer should do so in their presentation or poster. In an effort to make the abstracts as concise as possible and easy for meeting participants to read, the abstracts have been formatted such that they exclude references to papers, affiliations, and/or funding sources. Authors who wish to provide attendees with this information should do so in their presentation or poster.

Common abbreviations

Trench Models & Vapor Intrusion

Room: Pacific Concourse O   1:30 - 3 PM

T3-K.1  13:30  Estimating Exposure Concentrations for Trench Workers from Vapors Emanating from Soils and Groundwater using Computational Fluid Dynamics Modeling. Richter RO*, Schulman LL, DesAutels CG; Exponent

Abstract: Risk assessments often include a construction worker scenario that includes exposure to volatile organic compounds (VOCs) while working in a trench. Generally, exposure concentrations are estimated using a box models based on the dimensions of the trench, an average vapor flux into the trench, and an air exchange rate for the trench. While EPA and ASTM have scientifically sound methods for estimating the vapor fluxes entering a trench from soil and/or groundwater, neither has a method for reliably estimating the air exchange rate for a trench. An internet search for agency approved methods found values ranging from 2 to 360 air changes per hour (ACH), with little or no scientific basis for the values used. In contrast, for over a decade, atmospheric scientists have used computational fluid dynamics (CFD) models to estimate airborne chemical concentrations in urban street canyons, which can be viewed as large scale trenches. These models indicate that there is some reentry of contaminants into the box due to entrainment in fresh air entering the box. Thus, while these models can predict air exchange rates (ACH), they can also predict pollutant exchange rates (PCH) to account for this reentry. This presentation demonstrates the application of CFD modeling to estimate TCE vapor concentrations in a worker’s breathing zone emanating from both surrounding soils and underlying groundwater for various wind speeds, trench configurations, wind directions with respect to the trench.

T3-K.2  13:50  Calculating Inhalation Exposures for Utility Workers at Contaminated Sites. Custance R*, Heynes O, Villaroman C, Ettinger R; Geosyntec Consultants

Abstract: A variety of approaches have been proposed to estimate potential inhalation exposures to volatile organic compounds (VOCs) for workers in trenches and excavations at chemical release sites. An estimate of a representative VOC air concentration is typically calculated by combining (i) an estimate of the flux from groundwater, soil, or soil vapor to the trench volume with (ii) a dispersion factor based on the ventilation of the trench. Current existing methods commonly used in risk assessments incorporate a steady-state assumption for VOC flux and trench air exchange rates based on building air exchange rates to account for the reduced air flow anticipated in deeper trenches. These approaches may result in overly conservative estimates of exposure and are not necessarily reflective of actual conditions. This presentation provides a critical review of different methodologies that have been published and recommends technically-defensible methods for estimating utility worker inhalation exposures. Methods to calculate the steady state or transient flux of VOCs from the source zone to the trench air space will be presented. Additionally, methods to estimate the amount of air dispersion within the trench air space will be discussed. Current approaches will be compared to computational fluid dynamic (CFD) calculations that have been performed to provide estimates of the dispersion of VOCs in ambient air. The CFD analysis examines the dependence of trench dimensions and average ground-level wind speed on the air exchange rate for the worker exposure area. Examples of the impact of applying this approach will be presented and uncertainties in the calculation methodologies will be discussed.

T3-K.3  14:10  The Use of Multiple Lines of Evidence to Identify an Indoor Air Source of Volatile Constituents. Sager SL*, Frizzell A, Darby T, Davis A, Shirley P; ARCADIS U.S., Inc.

Abstract: Historic groundwater and soil gas data were used to predict migration of volatile organic compounds (VOCs) to indoor air throughout an industrial area. The modeling results were used to focus further investigations and limit the need for sub-slab soil gas and indoor air samples. Based on the modeling results, two buildings were selected for paired sub-slab soil gas and indoor air sampling to clarify whether or not constituents detected in impacted groundwater were migrating in the gas phase from the subsurface into the buildings. The exposure assessment was designed to focus on those constituents that could be traced back to the groundwater impacts. Thus, the indoor air sampling results were compared with ambient air data to exclude any constituents not related to the vapor intrusion pathway. Next, the sub-slab soil gas data were compared with indoor air data to exclude any constituents either not detected in indoor air or were present in indoor air and not in sub-slab soil gas. The remaining constituents were evaluated for the likelihood that they originated from indoor sources. This paper will discuss the indoor air sampling results within the context of identifying potential sources of constituents and quantifying exposure. Confounding issues that increased the uncertainty in the evaluation were the nature of the materials stored in the buildings as well as the locations of the measured indoor air concentrations with respect to the suspected source of the VOCs in groundwater. In the end, the sources of indoor air constituents were identified based on an overlay of groundwater, soil gas, sub-slab soil gas, and indoor air concentrations with chemicals and materials used in the building for operations and storage.

T3-K.4  14:30  Indoor Air Exchange Rates in Developing Countries: A Pilot Study in Rural Peru . Williams PRD*, Unice K; E Risk Sciences, LLP, Boulder, CO; ChemRisk, Pittsburg, PA

Abstract: The rate at which outside air replaces indoor air in a given space can influence indoor air quality and is a key parameter in many exposure models. Although published air exchange rate (AER) data are available for residences and workplaces in developed countries, such as the United States, few data are available for less developed countries, particularly in rural areas where building materials and housing characteristics can vary widely. In this pilot study, we measured the AER in two housing units located in rural Peru under different test conditions, and compared our results to reported values in the published literature. The field test method consisted of releasing a tracer gas (SF6) and using a Miran SapphIRe Analyzer to log real-time results in 30 to 60 second intervals. The number of air changes per hour was estimated by plotting the concentration decay of SF6 as a function of time using ASTM standard E741-00. Measured AER values in different rooms (e.g., kitchen, living room, bedroom, bathroom) were found to range from approximately 2 to 6 air changes/hr when all exterior windows and doors were closed, 6 to 12 air changes/hr when a combination of exterior windows and doors were open and closed, and 12 to 20 air changes/hr when all exterior windows and doors were open. The primary source of air exchange was from leakage from openings around windows and doors and holes in exterior walls. In general, measured AERs in housing units in rural Peru were found to be greater than those measured in tight homes in developed countries. These data should provide useful information for risk assessors and risk managers with respect to understanding indoor contaminant exposures among rural populations in less developed countries and establishing priorities for risk management.

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