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International Conference 2011

Uranium, Mining and Hydrogeology VI

Workshops UMH II

Workshop 1: Risk Analysis/Cost Benefit

Chair: Donald Metzler

Participants in the Risk Analysis/Cost Benefit Workshop corroborated that the countries they represented use similar approaches to quantify risk to human health and the environment.

A discussion about use of risk assessment methodology to evaluate human health risks of uranium mill tailings and contaminated groundwater at inactive uranium processing sites substantiated that most countries use risk assessment to assist in making remedial action decisions. Participants compared methodologies using deterministic and probabilistic approaches. They presented their experiences with the use of probabilistic distributions for exposure variables where sufficient data exist and for simulating predicted exposure distributions with Monte Carlo techniques. Participants agreed that realistic predictions must dominate and that overly conservative calculations are not representative of sound science.

Another topic of interest was remedial action goals, such as prescriptive standards versus risk-based standards. When working under a risk-based scenario, both carcinogenic and chemical toxicity risk are important factors to be considered. Uranium was used as an example of a soluble constituent that exhibits potential health risk to human health because of carcinogenic effects, such as excess cancer risk and chemical toxicity to organs. It was noted that action levels or maximum concentrations limits continue to be debated about permissible levels of uranium concentrations in drinking water. Sulfate was also mentioned with respect to uncertainty associated with permissible levels that are considered safe.

Workshop participants assessed the use of flow-and-transport modeling as a integral element of predicting risk. A participant representing Namibia presented examples of exposure assessments and pathway analysis and related her experience with exposure assessment assumptions, such as hypothesizing a farm family living x distance from a mill tailings compound. In this scenario, assumptions were made for ingestion rates, body weight, exposure duration, and indirect pathways (such as uptake of contaminants into vegetables, milk, and meat). Contaminant flow and transport was modeled from a point of compliance at the tailings compound along a path to a point of exposure at the hypothetical farm. Participants emphasized that modeling predictions must be followed by a reasonable degree of long-term monitoring to verify assumptions and predictions.

Risk communication was of interest because the intent of risk assessment is to provide the public and remedial action decision-makers with information about health risks that might be expected at a site in a manner that is easily understood. A quote from a professional risk management communicator was reiterated: Risk = Perception + Outrage. This quote set the stage for a robust discussion on risk communications and public involvement. Participants generally agreed that a predicted risk determination must be communicated effectively to avoid excessive project costs. An Australian participant related a number of experiences with communication risk, community involvement, and the process of building public trust.

A discussion of risk integrated with cost-benefit analysis included the concept of Best Available Technology Not To Exceed Excessive Cost. A participant from South Africa shared his experience with this concept and noted that thresholds and decision points are often nebulous.

© A. Berger <umh@geo.tu-freiberg.de>, 17.05.2010, http://www.geo.tu-freiberg.de/umh/UMHII_Workshop1e.htm