T1-G
Risks and decisions for contaminated water and sedimentsGuilford 9:40 AM
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| Chair(s): Todd Bridges Todd.S.Bridges@erdc.usace.army.mil
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| This session focuses on risks related to contaminated water and sediments. It discusses the development of predictive tools to assess potential risks caused by groundwater contamination, results related to modeling arsenic risks, and issues related to managing uncertainty to make risk-informed decisions about contaminated sediments. |
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T1-G.1 9:40 AM Development of predictive tools to assess potential risks caused by groundwater contamination. Kohnke MW*, Simon JJ; Simon & Associates, Inc. kohnkemw@simonassoc.com
Abstract: Contamination of groundwater supply by a sequence of spill events could disrupt the delivery of vital human services in a region, threatening public health and the environment, and possible causing loss of life. Different as with surface water resources, contamination of groundwater resources can be achieved with little volumes of contaminant. For example, one gallon of gasoline is able to pollute 1,000,000 gallons of groundwater. Once an aquifer is contaminated its clean-up may take a couple of years and is very expensive. Across the country aquifer systems extend over vast areas and ownership and operation responsibility are both public and private, but are overwhelmingly non-federal. Since 2001, dam operators and water and wastewater utilities have been under heightened security conditions and are evaluating security plans and measures. Due to the fact that assess to groundwater can be provided through percolation in porous media and infiltration at individual wells (active and abandoned), individual protection measures at the different well fields are very expensive to maintain, being aquifers therefore very vulnerable. Complete protection of aquifers will never be possible, however, being prepared when the catastrophic event happens and having the right tools and procedures in place to determine the right measures, can be achieved at a relatively low cost. Numerical groundwater flow and contaminant fate and transport models have been used successfully in the past as a tool to manage groundwater quantity and quality and are well suited to be used to evaluate the effects of a contaminant as it starts to disperse through the aquifer after approaching the water table. This paper discusses how numerical models can be utilized as effective management tools to address the risk of groundwater contamination and to develop the right measures to contain the damage caused by unintentional and intentional contamination.
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T1-G.2 10:00 AM A framework of risk-based decision making by characterizing variability and uncertainty probabilistically: Using arsenic in dinking water as an example. Chu H*, Crawford-Brown D; Carolina Environmental Program, UNC-Chapel Hill hachu@email.unc.edu
Abstract: Risk-based regulatory decisions generally apply a margin of safety meant to guard against underestimation of risk in the face of inter-subject variability and uncertainty. Since these two components often are unknown or only vaguely characterized, the decisions involved usually employ conservative default assumptions concerning the margin of safety, resulting in regulatory limits that may be more (or less) health protective than necessary if variability and uncertainty could be characterized probabilistically. As a result, it remains impossible in most cases to determine the degree of protectiveness inherent in a standard. The debate about maximum contaminant levels (MCLs) of arsenic is an example. At present, we can only get a vague idea that lowering MCLs results in larger margins of safety, but at the expense of greater compliance costs. If the magnitude of this margin of safety is not taken into account, it is possible that an MCL may be established based on a significantly larger margin of safety than is necessary, reasonable or consistent with that applied to other contaminants. Thus an unnecessarily expensive treatment policy may be selected. In this study, a new framework of probabilistic risk-based decision making was developed. A meta-analysis was conducted for arsenic in drinking water by combining several epidemiological studies from various regions (such as Taiwan, US, Argentina, Chile and Finland). Then the results of the meta-analysis were incorporated into the framework to characterize the margin of safety through variability and uncertainty analyses. The final product of this study is a method of probabilistic risk assessment that better deals with variability and uncertainty issues. This risk assessment methodology can help decision-makers make optimal determinations on regulatory limits for a contaminant that adequately protect human health with an ample margin of safety at a more reasonable cost than currently is the case.
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T1-G.3 10:20 AM Humans at arsenic risk: An integrated spatio-chemical methodological approach. Khan NI*, Owens GP, Bruce D, Flaxman M, Naidu R; Univesrsity of South Australia, ESRI nasreen.khan@unisa.edu.au
Abstract: Over 85 million people are potentially at risk due to exposure to arsenic (As) in the drinking water of Bangladesh. The developed methodology is used to assess human exposure from arsenic contaminated soil, water and food by integrating various exposure pathways into a geospatial environment. Concentration of As in water, food, and local edible vegetables are used as potential As exposure indicators. A GIS was used as the platform for the development of an As exposure risk model. GIS was chosen for its capability to provide a spatial and visual dimension to the exposure source - pathway - receptor paradigm. The methodology was developed using spatial interpolation techniques to model the exposure source - pathway - receptor paradigm in combination with quantitative risk equations to evaluate potential human heath risk from exposure to a combination of contaminated soil, water, and food. The develop methodology provides the capability of quantitative As concentrations mapping in different environmental media including spatial distribution of As concentrations and the exposure induced human health risk. The exposure assessment framework focuses on understanding the complex pathways of human As exposure via different environmental media. An integrated exposure assessment methodology was used to define the relationships between exposure and human health risk and its interaction in spatio-demographic context. The developed methodology is suitable for modeling exposure source - pathway - receptor paradigms and quantitative risk assessment. Exposure and human health risk assessment is dependent on a large number of input parameters derived from a variety of different sources and of variable data type and may include chemical, demographic, dietary intake, location, landuse, geology, and/or guideline values. The inherent relationship between different datasets requires special data linking technique in GIS to calculate total exposure and risk. In the developed methodology chemical data was fit to a spatial composite.
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T1-G.4 10:40 AM Managing uncertainty to make risk-informed decisions about contaminated sediments. Bridges TS*, von Stackelberg K, Vorhees D, Butler C, Cura J, Greges M, Reiss M; US ERDC, Menzie-Cura and Associates, US ACE, US EPA Todd.S.Bridges@erdc.usace.army.mil
Abstract: This paper will describe how the regulatory community concerned with placing sediments at the Historic Area Remediation Site (HARS) on the NY Bight is incorporating site-specific information and uncertainty into its decision-making approach. Limited and uncertain data often challenge regulators in reaching credible conclusions about the extent, magnitude, and potential impact of risk management options. One response to this challenge has been to invest in additional data collection and research, which may provide additional insights into the processes relevant to understanding risk, but generally cannot resolve all uncertainties. Managing and addressing this residual uncertainty represent significant challenges to decision-making. At the HARS, past regulatory evaluations for sediment placement were performed through a comparison of bioaccumulation test results to deterministically-derived tissue based guidelines. More recently, regulators have considered risks to fish and humans from contaminant bioaccumulation and trophic transfer. Regulators, recognizing important uncertainties in these evaluations, commissioned two site-specific studies: (1) a fish tagging study to learn more about how fish behavior may affect their exposures; and (2) a creel survey to refine fish ingestion rates for the angler population fishing near the HARS. Refined and updated estimates of these and other inputs to the evaluation were used to develop a remodeled approach for evaluating sediments based on estimating risks from cumulative contaminant effects. This approach factors uncertainty and variability in input parameters into bioaccumulation and risk modeling using two-dimensional Monte Carlo analysis. Model outputs are included in a decision-support tool that allows decision-makers to explore and factor uncertainty into their conclusions about risks and their decisions as to how to manage those risks.
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