Worthiness of complex groundwater models for decision making— How can we balance complexity with 
simplicity? 

   
Complex mathematical models are routinely used by groundwater hydrologists to predict contaminant 
concentration levels in polluted aquifers.  These predictions are then used in risk-assessment and 
epidemiological studies, which are often completed either for resolving a court case or for developing 
a public-policy solution.  Typical groundwater modeling studies utilize a variety of mathematical 
models with complexity levels ranging from simple analytical solutions to detailed three-dimensional 
numerical solutions that simulate multi-phase, multi-species, reactive transport systems.  The goal of 
this discussion is to explore the value of using complex numerical models to resolve large, 
field-scale, practical problems that have limited data.  I will review a chlorinated solvent 
contamination problem that occurred at a military site in Camp Lejeune, North Carolina, and will use it 
as an example to explore the limits of complex numerical modeling exercises.  The lessons learned from 
the study will be used to reflect upon the following two questions related to model complexity:  How 
should we decide how much is enough?  Who should decide when enough is enough?   This presentation will 
be based on a project I reviewed while I served as a member of National Academy of Sciences and 
Engineering study.  The goal of this congressionally mandated study was to review available scientific 
evidences on the association between adverse health effect s and exposure to a contaminated water 
supply system at the U.S. Marine Corps Base Camp Lejeune (CLJ) in North Carolina.  The detailed NRC 
study was released in June 2009, and is currently available at this website:  
http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=12618. Also, a brief summary of 
various modeling issues related to this work was published in the following article:  Clement, T.P. 
2010.  Complexities in Hindcasting Models—When should we say enough is enough?  Ground Water, Vol. 49, 
No. 5 p. 620–629. 

Biosketch:  Dr. Prabhakar Clement is currently the Harold Vince Groome Endowed Professor of 
Environmental Engineering in the Department of Civil Engineering at Auburn University.  Before, he 
worked at the Department of Environmental Engineering, University of Western Australia for 3 years 
(2000-2002), and at the Battelle Pacific Northwest National Laboratory, Washington for 7 years 
(1994-2000).  Dr. Clement is the lead author of the widely used MODFLOW-family groundwater model RT3D.  
He has supervised over 10 PhDs, authored over 100 peer-reviewed publications which have received over 
3900 Google Scholar citation with an H-index of 33; he is an elected ASCE Fellow.  More recently, he 
won the John Hem Award for Excellence in Science & Engineering from the National Groundwater 
Association.  He has served as associate editor for several leading environmental journals including 
Water Resources Research, and has served on several National Academy and NSF panels.  For more details 
visit: http://www.eng.auburn.edu/~clemept/