Response Surface Method Coupled with First-Order Reliability Method Based Methodology for Groundwater Flow and Contamina
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Response Surface Method Coupled with First-Order Reliability Method Based Methodology for Groundwater Flow and Contaminant Transport Model for the Uranium Tailings Pond Site Manish Chopra & Rohit Rastogi & A. Vinod Kumar & Faby Sunny & R. N. Nair
Received: 1 August 2011 / Accepted: 12 December 2012 / Published online: 8 January 2013 # Springer Science+Business Media Dordrecht 2013
Abstract Groundwater flow and contaminant transport modelling is carried out to predict the concentrations of radionuclides in groundwater beneath the tailings pond. This is used as a tool for radiological impact assessment studies. The geo-hydrological parameters involved in the modelling exhibit inherent uncertainty associated with their values. This uncertainty may get propagated to the model output, i.e. the dose to the public. The propagation of the uncertainty in the input parameters to the output is modelled using suitable methods of probabilistic analysis. Response surface method coupled with first-order reliability method is used to develop a methodology for estimating the probability that the dose rate value through drinking water pathway at a location around the tailings pond exceeds the WHO guidelines for drinking water, termed as the probability of exceedance of acceptable levels. This method also gives the estimate of sensitivity of the probability of exceedance to the different input parameters. It is observed that the probability of failure decreases as the distance from tailings pond centre is increased and beyond a M. Chopra (*) : A. V. Kumar : F. Sunny : R. N. Nair Environmental Assessment Division, Bhabha Atomic Research Centre, Mumbai 400 085, India e-mail: [email protected] A. V. Kumar e-mail: [email protected] F. Sunny e-mail: [email protected] R. N. Nair e-mail: [email protected] R. Rastogi Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai 400 085, India e-mail: [email protected]
distance of around 0.5 km from tailings pond centre, the probability reduces to zero. The work also brings out the importance of quantifying the uncertainty in case of actual field problems where there is wide variation in the values of the various parameters within the domain under study. Keywords Tailings pond . Groundwater . Contaminant transport . Uncertainty . Reliability
1 Introduction The uranium milling waste stored in the tailings pond contains all of the naturally occurring radioactive elements found in the uranium ore. The tailings pond is constructed in the topographic depressions and is properly engineered with dam to hold the tailings for long time with structural stability. In due course, the radionuclides may leach into the unconfined aquifer and contaminate the groundwater. Groundwater flow and contaminant transport models are used for the evaluation of concentrations of radionuclides in the aquifer on temporal and spatial scale. The concentrations are used for the radiological impact assessment of the tailings pond site in terms of dose to the public due to the radioactive content of the tailings.
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