Grantee Research Project Results
1999 Progress Report: An Efficient Reliability-Based Approach to Aquifer Remediation Design
EPA Grant Number: R827126Title: An Efficient Reliability-Based Approach to Aquifer Remediation Design
Investigators: Reeves, Howard W. , Dowding, Charles H. , Igusa, Takeru
Institution: Northwestern University
EPA Project Officer: Aja, Hayley
Project Period: September 1, 1998 through August 31, 2000 (Extended to June 30, 2001)
Project Period Covered by this Report: September 1, 1998 through August 31, 1999
Project Amount: $142,198
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities
Objective:
The objective of this research project is to implement an efficient approach to quantitatively link site characterization and site remediation for sites with contaminated soil and groundwater. The research addresses two key questions imposed on site characterization activities: Are there enough site data to design a system and to assess the confidence of success for the system addressing contamination at the site? Where and what data should be collected to increase confidence of success in the proposed remedial design?
Progress Summary:
Numerical models often are used for site-specific analysis and design of cleanup schemes for contaminated soil and groundwater. These models require a large suite of input parameters to define the geometry of the geologic setting, the hydrogeologic parameters of the materials at the site, and the chemical and biological processes impacting the contaminant. The reliability analysis implemented in this research builds on this numerical modeling by including both the best estimate of the input parameters and an estimate of the uncertainty in these parameters. With this information, the behavior of the contaminant is simulated and the uncertainty of this simulation also is estimated. System reliability, which is an indication of the probability of success of a project, is determined by combining the simulated behavior, its estimated uncertainty, and an imposed desired goal. Various remedial schemes can be evaluated by modeling each scheme and comparing the reliability of each. Additionally, the method allows the important data impacting the reliability at the site to be determined and thereby may be used to guide additional site characterization efforts.
The three main challenges in implementing this method are: (1) determination of input data estimates and uncertainty; (2) computation of system response and required numerical information allowing for the estimation of the uncertainty in the system response; and (3) evaluation of the reliability of the system given the computed information. We have made substantial progress in each of these three areas.
To determine the input parameter values, a Bayesian or conditional probability approach has been adopted. In this approach, observations from a site are combined with geologic or engineering judgment in a quantitative fashion. We have developed an approach that generalizes traditional geostatistical techniques by allowing the parameters that are embedded within kriging to be uncertain within the computations. The approach yields the required input values and covariance matrices used in the estimation process. We are continuing to work on the implementation of the Bayesian approach and plan to test its applicability on a range of geologic settings.
The numerical model tested this past year uses two-dimensional flow and contaminant transport equations to describe the areal migration and fate of a contaminant at a site. We allow the thickness of the aquifer, the initial concentration distribution of the contaminant, and the first-order decay coefficient describing degradation of the contaminant to be uncertain in the analysis. A first-order Taylor series approach is used to determine the reliability of a cleanup scheme proposed for a hypothetical site. One key to the efficient computation of the reliability is the direct computation of derivatives required by the Taylor series to relate input uncertainty to system uncertainty.
The analysis of the computational results lies in the estimation of the system reliability. This reliability is estimated by comparing the simulation results from the design model to imposed target values at given points in the domain. Typically, the results of the transport model are used to compare estimated concentrations to maximum allowable concentrations for the contaminant at key points in the domain. The difference between the simulated and maximum value is divided by the estimated uncertainty in the simulated concentration to yield the reliability in the estimate. Values of reliability near zero imply that the system is not reliable and must either be redesigned or additional data are required to decrease the uncertainty in the simulation result.
The key results for this year of the project include: validation of the efficiency of the approach as compared to methods that use numerical methods to determine the required sensitivities or methods based on Monte Carlo simulation, demonstration that the technique can be used to compare different remediation schemes for a hypothetical site, demonstration that the technique can be used to compare the impact of different input parameter uncertainties, and demonstration that the approach is applicable to transient contaminant transport simulations. We have completed work simulating two-dimensional steady-state flow with transient contaminant transport and are currently implementing the methods in a true three-dimensional groundwater flow and transport model, which will allow us to examine more general geologic settings.
Future Activities:
For the second year of this project, the complete two-dimensional results will be submitted for publication in an archived journal. We will complete implementation of the approach to the transient flow and contaminant transport equation in three dimensions. Once the approach is implemented and tested, we will use the numerical model and reliability tools to explore different hypothetical geologic settings and contaminant scenarios to test the applicability of the scheme to a wide range of problems. In this testing phase of the research, we will identify areas of concern for future work and submit our research findings for publication.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
groundwater, remediation, cleanup, decision making, Bayesian, environmental engineering, hydrology, geology, modeling., Air, Scientific Discipline, Waste, Remediation, Ecological Risk Assessment, Engineering, Environmental Chemistry, Engineering, Chemistry, & Physics, Groundwater remediation, Hydrology, three dimensional transport model, contaminant transport, groundwater flow, aquifer remediation design, hydrogeologic unit boundry, water quality, computationally efficient algorithm, site characteriztion, fate and transportRelevant Websites:
http://www.civil.nwu.edu/people/reeves.html 
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.