William Simpkins

Bio

Research

My research focuses primarily on groundwater flow and geochemistry in aquitards (confining units) of glacial origin (primarily till and loess). Within that broad framework, I investigate physical groundwater flow and chemical properties of groundwater in the till; use radioactive and stable isotopes to elucidate groundwater source and age; describe and quantify groundwater transport of agricultural chemicals in till, including the interaction of groundwater with lakes and streams and tile drainage; and examine the vertical integrity of the aquitards using anthropogenic tracers and aquifer tests. Research areas are located in Iowa and Minnesota. Our research group has been in the forefront of describing the unique redox geochemistry of till aquitards of the Des Moines lobe (Simpkins and Parkin, 1993), as well as the impact of till fractures on groundwater flow, hydraulic conductivity, and contaminant transport (Helmke et al. 2005a; 2005b). Recent research has shown, using field data and the HydroGeoSphere model, that the representative elementary volume (REV) of fractured till can be estimated (Young et al. 2020). We are also addressing how well till fractures observed in small diameter cores predict flow and solute transport properties at larger scales (Young et al. 2021). In association with the U.S. Geological Survey, Upper Midwest Water Science Center (Minnesota office) and with funding from the Legislative-Citizen Commission on Minnesota Resources, our group has been involved in estimating the vertical flux of water and penetration of anthropogenic contaminants to underlying confined (glacial) aquifers in four till aquitards of differing textures and age in Minnesota. The study, which is helping to quantify the sustainability of these aquifers for future water supply, was published at the end of 2020 (Trost et al. 2020).

Since 2006, our research group has also been investigating the hydrogeology of the Ames aquifer, which provides the entire water supply to the City of Ames. This investigation has involved a hydrogeological characterization and 3-D MODFLOW model of Ada Hayden Lake (the city’s backup water supply); an analytic element model of the Ames aquifer; and a geochemical characterization of the aquifer, including redox parameters, stable (δ18O and δ2H) and radioactive isotopes (3H, 3H/3He, 14C-DIC), SF6, and Cl/Br ratios. A study on groundwater flow and human enteric virus transport in the aquifer is in review. Continuing work involves completing a 3-D MODFLOW model of the aquifer (to assess future sustainability) and writing up heat transport and denitrification studies in the aquifer at the River Valley Park site. I continue to research the stable isotope record of precipitation in central Iowa, and a manuscript updating the Simpkins (1995) paper is in preparation.

Selected Publications

• Trost, J.J., A. Maher, W.W. Simpkins, A.N. Witt, J.R. Stark, J. Blum, and A.M. Berg, 2020. Hydrogeology and groundwater geochemistry of till confining units and confined aquifers in glacial deposits near Litchfield, Cromwell, Akeley, and Olivia, Minnesota, 2014–18: U.S. Geological Survey Scientific Investigations Report 2020–5127, 80 p., DOI: 10.3133/sir20205127.
• Young, N.L., W.W. Simpkins, and R. Horton. 2021 Are visible fractures accurate predictors of flow and mass transport in fractured till? Results from small-diameter, column tracer experiments. Groundwater. DOI: 10.1111/gwat.13013
• Young, N.L., W.W. Simpkins, J.E. Reber, and M.L. Helmke. 2020. Estimation of the representative elementary volume of a fractured till: a field and groundwater modeling approach. Hydrogeology Journal, DOI: 10.1007/s10040-019-02076-y.
• Young, N.L., J.E. Reber, and W.W. Simpkins. 2019. FracKfinder: A MATLAB toolbox for computing three-dimensional hydraulic conductivity tensors for fractured porous media. Groundwater. DOI: 10.1111/gwat.12837.
• Marquardt, K.E., M.L. Rankin, and W.W. Simpkins. 2013. Town meets gown: Creating a collaborative process for expanding a university’s recycling program while supporting a city’s waste diversion efforts. Sustainability: The Journal of Record 6(9): 104-114.
• Simpkins, W.W. 2006. A multi-scale investigation of ground water flow at Clear Lake, Iowa. Groundwater 44 (1):35-46.
• Helmke, M.F., W.W. Simpkins, and R. Horton. 2005a. Simulating conservative tracers in fractured till under realistic timescales. Groundwater 43 (6):877-889.
• Helmke, M.F., W.W. Simpkins, and R. Horton. 2005b. Fracture-controlled transport of nitrate and atrazine in four Iowa till units. J. Environ. Qual. 34:227-236.
• Helmke, M.F., W.W. Simpkins, and R. Horton. 2004. Experimental determination of effective diffusion parameters in fractured till. Vadose Zone Journal 3:1050-1056.
• Burkart, M.R., W.W. Simpkins, A.J. Morrow, and J.M. Gannon. 2004. Occurrence of total dissolved phosphorus in surficial aquifers and aquitards in Iowa. J. Amer. Water Resources Assoc. 40(3):827-834.
• Rodvang, S.J. and W.W. Simpkins. 2001. Agricultural contaminants in Quaternary aquitards: a review of occurrence and fate in North America. Hydrogeology Journal 9(1):44-59.
• Eidem, J.M., W.W. Simpkins, and M.R. Burkart. 1999. Geology, groundwater flow, and water quality in the Walnut Creek watershed. Jour. Environ. Qual. 28:60-68.
• Cambardella, C.A., T.B. Moorman, D.B. Jaynes, J.L. Hatfield, T.B. Parkin, W.W. Simpkins, and D.L. Karlen. 1999. Water quality in Walnut Creek watershed: nitrate-nitrogen in soil, subsurface drainage water, and shallow groundwater. J. Environ. Qual. 28:35-44.
• Simpkins, W.W. 1995. Isotopic composition of precipitation in central Iowa. Journal of Hydrology 172: 185-207.
• Simpkins, W.W. and T.B. Parkin. 1993. Hydrogeology and redox geochemistry of methane in a late Wisconsinan till and loess sequence in central Iowa. Water Resources Research 29(11): 3643-3657.
• Simpkins, W.W. and K.R. Bradbury. 1992. Groundwater flow, velocity, and age in a thick, fine-grained till unit in southeastern Wisconsin. J. of Hydrology 132: 283-319.

Awards

• Early Achievement in Departmental Leadership Award, College of Liberal Arts and Sciences (2017)
• George Burke Maxey Distinguished Service Award, Hydrogeology Division, Geological Society of America (2015)
• Outstanding Faculty Member, selected by the Phi Kappa Theta fraternity (2014)
• Outstanding Teaching Award, ISU College of Liberal Arts and Sciences (2008)
• College of Liberal Arts and Sciences 150 Most Fascinating People (2007)
• College of Agriculture Team Award, Agroecology Issue Team (2003)
• Master Teacher Award, ISU College of Liberal Arts and Sciences (2002)
• Fellow, Geological Society of America (2002)

Service

• General Meeting and Section Chair, Geological Society of America, North-Central Section meeting, Ames, Iowa (April 2018)
• Finance Committee, Geological Society of America (2016-2019)
• Department Chair and Smith Family Foundation Departmental Chair in Geology, Department of Geological and Atmospheric Sciences, Iowa State University (2014-2017)
• Councilor, Geological Society of America (2012-2016)
• College of Liberal Arts & Sciences, Promotion and Tenure Committee (2011-2014)
• Chair, Hydrogeology Division, Geological Society of America (2002)
• Associate Editor, Ground Water (1996-2005)
• CUAHSI Campus Representative (2000-2015)
• Topical Session Co-Chair, Hydrogeology of Glaciated Terrain: Linking Glacial Geology, Quaternary History, and Groundwater Research, Geological Society of America Annual Meeting, Minneapolis, MN October 9-12, 2011
• President, ISU Chapter of Sigma Xi (2008-09)