T4-J
Methods and applications of statistical methods in risk analysisGibson 4:00 PM
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| Chair(s): Wendy Swanson wswanson@neptuneinc.org
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| This session begins with a comparison of statistical methods in evaluating non-detects in risk assessment, then focuses more on specific applications of risk analysis in the context of decision making. It includes discussion of a strategy for identifying areas of concern at a contaminated site and the use of risk analysis to explore the role of desalination technologies in contributing a resolution to the water dispute between Israel and her neighbors. The session also includes consideration of the strengths and weaknesses of using epidemiologically-derived risk estimates for concentration-response relationships and discusses these in the context of developing air quality (and other) standards. |
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T4-J.1 4:00 PM Comparison of statistical methods in evaluating non-detects in risk assessment. Luke N*, Luke R, Julias C, Mayo J; Camp Dresser & Mckee Inc. luken@cdm.com
Abstract: The most common approach to handle non-detects in both human health and ecological risk assessments is to use half of the detection limits for non-detects in the calculation of summary statistics, exposure point concentrations, and risk estimates. This approach assumes that the average value of non-detects could be as high as half the detection limit. However, when the number of non-detects in a data set is large or when the detection limit values are high, such as in the case of Contract Required Quantation Limits under the Contract Laboratory Program, or when there are dilutions or matrix interferences, using half the detection limit may produce results that are highly biased and, thus, exposed to overly conservative risks. To improve the accuracy of the calculation of the concentration term when considering non-detects, various statistical methods and analyses have been recommended to evaluate the non-detects, especially, when non-detects make up a large fraction of the data set. The complexity of statistical analysis is usually dependent on the distribution of data (i.e., normal, lognormal, gamma, or non-parametric) and the percentage of data values below the detection limits in a data set (e.g., 15%, 50% or even as high as 75%). Various statistical approaches and methods such as substitution of a single value, maximum likelihood estimation methods, and imputation methods, for evaluating non-detects in the calculation of the concentration term are used to compare differences in the computed concentrations of the test data sets. Subsequently, the computed concentrations are employed in determining the impact on the risk estimates in risk assessments.
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T4-J.2 4:20 PM A critical evaluation of the use of epidemiological risk estimates as the basis of concentration-response functions. Sulsky SI*, Mundt KA, Scofield R, Bigelow C; ENVIRON International Corporation, University of Massachusetts - Amherst ssulsky@environcorp.com
Abstract: Dose-response assessment, or the evaluation of the relationship between dose of exposure and risk of disease, is a key tool of both epidemiology and toxicology. A potential advantage of epidemiological over toxicological data is its basis in human populations, which removes the need to extrapolate across species. Epidemiologically derived dose-response assessments are often used, correctly, in developing public health policies such as air quality standards. There are challenges, however. Changes in standards are sometimes rationalized by calculations purporting to describe the number of deaths or cases of disease averted by the proposed change. The assumptions implicit in such calculations are not necessarily valid and, therefore, should be examined. Especially problematic assumptions include the following: the observed association is causal; each risk factor exerts independent or non-competing effects; any intervention implemented will be completely effective in removing or reducing exposure; and removal or reduction of exposure will result in the risk of the disease or cause of death declining proportionately to the change. These assumptions will be discussed in the context of air quality standard setting. The goal is to identify the strengths and acknowledge the limitations of epidemiologically derived risk estimates when used to calculate concentration-response curves so that uncertainties will be better understood and accounted for in the development of air quality (and other) standards.
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T4-J.3 4:40 PM Identifying target areas on the former Camp Beale: Statistical and qualitative tools. Swanson WL*, Lancaster VA, Michael DI, Neptune MD, Barton B; Neptune & Co Inc, Earth Tech wswanson@neptuneinc.org
Abstract: A Site Inspection has been conducted by the USACE, Sacramento District on a 62,350 acre area within the Former Camp Beale, located in Yuba and Nevada Counties, CA. This study followed the latest Federal policy for investigation of Formerly Used Defense Sites. Field data collection was performed between June 2005 and February, 2006. The primary objective of the SI was to determine which portions of the former Camp Beale are munitions target areas that should be further evaluated in a Remedial Investigation, and which areas are non-target areas that can be addressed by continued "risk-management" activities. To support the stated objective, digital geophysical and GPS data were collected along parallel transects spaced to have a high probability of intersecting debris fields indicative of a target area as small as 1000 ft in diameter. A subset of the geophysical anomalies were intrusively investigated following a decision rule designed to avoid missing Munitions and Explosives of Concern (MEC) or Munitions Debris (MD), while minimizing the number of digs required to characterize the area. Transects were divided into 400 ft segments; the scale at which intrusive investigations were performed, and data collected within each segment combined to determine whether evidence of MEC or MD was present. For segments where geophysics and/or dig data was not collected (e.g., bio-concerns, no right of entry or steep terrain) quantitative and qualitative methods were used to fill in the map to the degree supported by existing data. The field data were analyzed using pattern recognition and classification techniques. Statistical model based cluster algorithms using regression trees, quadratic discriminant and flexible discriminant classifiers were compared and ultimately used to generate maps denoting potential target areas. These maps were then refined by considering additional layers of information, and the level of confidence in statistical predictions.
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T4-J.4 5:00 PM An assessment of desalination technologies in contributing a resolution to the water dispute between Israel and her neighbors. Lipchin CD*, Brenner S; Arava Institute for Environmental Studies clive@arava.org
Abstract: The dispute between Israel and the Arab countries in the Middle East has already lasted for many years with grave consequences to all parties. There are many causes and sources to the dispute: religious, national, economical, social and also control over resources, mainly water. To assume that solution to the water crises in the area will bring about the final peace agreement is most probably wrong. However the efforts invested throughout the years on water and water related issues in the region by local and international stakeholders demonstrate the tremendous weight of the water problem in the overall search for an adequate solution. For example, the term "water rights" was mentioned frequently between the Israeli and Palestinian or Jordanian negotiators in the respective peace talks held in the last decade of the last century. Water rights do not mean only sovereignty over water sources but includes also quantitative and qualitative aspects, allocations, transport, treatment, wastewater treatment and transboundary effects as well as considerations of future needs and identification of new and alternative sources. Comprehensive risk assessment study of all the above-mentioned components may lead to the formation of a sophisticated joint water management program, isolated, as much as possible, from the other causes of the dispute. Such a program will not eliminate the dispute, but will definitely contribute to a major decline in the hostility and serve as an important tool in de-escalating the crises from reaching to regional and global levels. Desalination of sea or brackish waters has recently become a leading competitive technique for the production of substantial amounts of good quality water. Our aim is to try to investigate the magnitude and scope of the desalination process in the area as a potential means to play a significant role in the formation of the desired water management peace program.
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