David KahlerAssistant Professor
Bayer School of Natural and Environmental Sciences
Center for Environmental Research and Education
Education:Postdoctoral Research Fellow, University of Virginia, 2014-17
Science and Technology Policy Fellow, AAAS, 2012-14
Ph.D., Civil and Environmental Engineering, Duke University, 2011
M.S., Civil and Environmental Engineering, Duke University, 2009
M.S., Civil and Environmental Engineering, Cornell University, 2005
B.A., Physics and Mathematics, Skidmore College, 2002
Dr. Kahler teaches fundamental environmental science courses at Duquesne University. His research is in hydrology, primarily for use in international development.
Prior to joining the CERE faculty as a full-time professor in Fall 2017, Dr. Kahler was a postdoctoral fellow in the Water and Health in Limpopo, South Africa (WHIL) Innovation Program at the University of Virginia (UVA). His primary research at UVA was point-of- use drinking water treatment and water security in rural developing regions. An integral component of his international water security research focuses on the human right to water and water rights; this work is a collaboration with the University of Venda, South Africa. Prior to his research fellowship, he held an AAAS Science and Technology Policy Fellowship and at the Office of Water in the U.S. Agency for International Development. At USAID, Dr. Kahler focused on higher education partnerships between schools in the U.S. and partner countries on water and sanitation, and water resources. Additionally, David worked on agricultural water resources sustainability and was the technical representative for Securing Water for Food, a Grand Challenge for Development, a collaborative effort between the United States, Sweden, and The Netherlands.
Dr. Kahler earned his Ph.D. from Duke University in 2011. His dissertation research focused on the acceleration of pump-and-treat remediation by rapidly pulsed pumping. This work focused on pore-scale fluid mechanics. During graduate school, he was a part of a NSF Graduate Teaching Fellows in K-12 STEM Education program. Through this program, he assisted in a sixth-grade science classroom and ran an after school program that focused on technology encountered in everyday life. He also taught environmental engineering for two summer programs in India.
In his M.S. research at Cornell University, Dr. Kahler studied trends in observed evapotranspiration and precipitation, the so-called evaporation paradox. Through different measurement techniques, he determined that pan evaporation does not measure evaporation and even can show the opposite trend than actual evaporation. Dr. Kahler’s was graduated with a B.A. in Physics and Mathematics with a minor in Environmental Studies from Skidmore College in Saratoga Springs, New York. He spent most of his undergraduate summers as a Ranger at Philmont Scout Ranch in Cimarron, New Mexico.
Groundwater is a critical resource as the largest reservoir of liquid fresh water. Water systems that supply approximately one-third of customers in the U.S. and 98% household well withdrawals depend on safe groundwater. Unfortunately, groundwater is vulnerable to contamination by a large range of hazardous materials. Remediation of these contaminants is needed to return the aquifer to a usable condition; however, these efforts are lengthy and expensive.
Schematic of a typical pump-and-treat groundwater remediation. Image from the Pacific Northwest National Laboratories, US Department of Energy.
The most common method is pump-and-treat either alone or in conjunction with another technology. This approach uses pumps to remove contaminated water from an aquifer. One major bottleneck to remediation is that contaminants become trapped in pores that do not have a flow into and out of the pore; these pores have a dead end and thus are termed dead-end pores. Contaminants in these dead-end pores can remain in groundwater despite extensive treatment and release contaminant back into the aquifer after treatment.
Flow through porous media. (left inset) A poorly connected pore is in contact with the flow; however, the flow does not enter such an arrangement under steady flow. Molecular diffusion is the only mechanism that allows transport of contaminants between the two pore types. (right inset) Well-connected pores do not have any stable, isolated eddies and the fluid volume can be advected through them. Figure and caption from Kahler and Kabala , Image credit: Daphne Ching.
The US Environmental Protection Agency identified a serious and common problem in pump-and-treat remediation sites: after remediation ends and without external sources, contaminant levels in the aquifer rise again to unacceptable levels; this is known as rebound. There are several categories of sources for contaminant; however, the current work here focuses on matrix diffusion from dead-end pores. The only way that contaminant leaves dead-end pores is by diffusion. Rebound can pose a serious health risk to those who rely on the aquifer for water supply and will inevitably result in an expensive redeployment of remediation equipment.
Velocity (shown in m/s by color) of an axisymmetric dead-end pore of 0.001 m diameter with the expansion of 0.003 m diameter. Computational fluid dynamics (CFD) software is used to show the potential cleanup of remediation strategies.
Numerical and laboratory experiments confirm that sudden changes in flow rate can alter the fluid dynamics into and around these pores and improve contaminant removal. Rapidly pulsed flow (with a period on the order of one second) achieves significantly better contaminant removal than steady flow. These processes have not yet been fully exploited in groundwater remediation. Implementation of rapidly pulsed technology would utilize the same extraction and injection wells currently used in pump-and-treat remediation but could require replacement or modification of the pumps. Further research into this will include large-scale testing of rapidly pulsed pumping and improvements to numerical models to include various sorption processes and contaminant types.
Safe drinking water is needed for a healthy population. Furthermore, access to water resources is needed for economic development. The International Covenant on Human Rights has declared potable water as a human right, which was clarified in General Comment no. 15. The right to water is recognized by section 27 (1)(b) of the South African Constitution and South Africa has defined concrete minimum standards for safe drinking water in the Water Services Act 108 of 1997, and in regulations passed under the terms of this Act.
This work investigates the extent of the realization or non-realization of the right to water in a rural region of South Africa and its implications for the provision of water in South Africa and beyond. Despite constitutional obligations to provide safe water, accessibility and quality of water remain problematic in South African rural communities. Previous and current studies conducted in the Mutale River basin demonstrate that, in spite of existing infrastructure, water supply is unpredictably intermittent, which does not satisfy the required levels of access. The research also indicates that the water quality does not at all times adhere to the prescribed South African minimum standards, nor the recommended guidelines set by the World Health Organization for safe drinking water.
Kahler, D. M. and J. A. Smith, Mechanistic investigation of silver release from a porous ceramic for drinking water treatment. Under review.
Kahler, D. M. and Z. J. Kabala (2016), Acceleration of groundwater remediation by deep sweeps and vortex ejections induced by rapidly pulsed pumping: laboratory column tests. Under review.
Edokpayi, J. N., E. T. Rogawski, D. M. Kahler, C. L. Hill, C. F. Reynolds, E. Nyathi, J. A. Smith, J. O. Odiyo; A. Samie, P. Bessong, and R. A. Dillingham (2018), Challenges to sustainable access to safe drinking water in developing countries: A case study of water quality and water use practices in rural communities in Limpopo Province, South Africa, Water, 10(2), 159; doi:10.3390/w10020159.
Kahler, D. M., and Z. J. Kabala (2016), Acceleration of groundwater remediation by deep sweeps and vortex ejections induced by rapidly pulsed pumping, Water Resour. Res., 52(5), 3930-3940, doi:10.1002/2015WR017157.
Kahler, D. M., N. T. Koermer, A. R. Reichl, A. Samie, and J. A. Smith (2016), Performance and Acceptance of Novel Silver-Impregnated Ceramic Cubes for Drinking Water Treatment in Two Field Sites: Limpopo Province, South Africa and Dodoma Region, Tanzania, Water, 8(3), 95, doi:10.3390/w8030095.
Kahler, D. M., and W. Brutsaert (2006), Complementary relationship between daily evaporation in the environment and pan evaporation, Water Resour. Res., 42(5), doi:10.1029/2005WR004541.
Kahler, D. M., N. T. Koermer, A. R. Reichl, A. Samie, and J. A. Smith (2016), Performance and acceptance of a novel silver-impregnated ceramic tablet for drinking water treatment in Limpopo Province, South Africa. Accepted oral presentation. 2016 World Environmental and Water Resources Congress, West Palm Beach, Florida, May 2016.
Kahler, D. M. and J. A. Smith, (2015). Numerical models of a silver-based drinking water treatment technology. Accepted oral presentation. The Water Conference, University of Oklahoma, Norman, Oklahoma, September 2015.
Kahler, D. M. and Z. J. Kabala (2012), Novel Technology to Promote Mixing in Dead-End Pores Could Improve Pump-and-Treat, 2012 Fall Meeting, American Geophysical Union, San Francisco, CA, 3-7 December, Abstract H11A-1159.
Kahler, D. M. and W. Brutsaert (2005), Actual and Apparent Evapotranspiration in the Environment: A Study Toward the Resolution of the Evaporation Paradox, Eos Trans. AGU, 86(18), Jt. Assem. Suppl., Abstract H23B-10.
Kahler, D. M. (2011), The Acceleration of the Diffusion-Limited Pump-and-Treat Aquifer Remediation with Pulsed Pumping that Generates Deep Sweeps and Vortex Ejections in Dead-End Pores, Duke University.
Kahler, D. M. (2005), The Complementary Relationship for Daily Evaporation in the Environment, Cornell University.
Himes, K. E., C. McCormick, G. Bowser, J. Keen, D. M. Kahler, C. Ferland-Beckham, M.-V. V Johnson, and K. Pershell (2017), Fall into a new book, Science, 357(6355), 964 LP-969.
Kahler, D. M., and C. F. Reynolds (2017), Venda Study Area, version 1, doi:doi/10.18130/V3/KA3DZD. University of Virginia Dataverse
ENVI 451/551: Principals of Environmental Science, 3 cr., Fall and Spring
Environmental science is the study of the interaction between humans and the environment. This course will employ lectures, reading discussion and films to enable students to recognize the complex array of fact and theory that comprises this multi-disciplinary field. Students will understand the key elements of the physical and social sciences that make up this discipline, and apply quantitative and qualitative research methods to the analysis of environmental issues present in today's society and economy.
Textbook (Spring 2018): Wright and Boorse, Environmental Science: Toward a Sustainable Future (11th, 12th, or 13th edition)
ENVI 549: Quantitative Methods, 3 cr., Spring 2018
The primary focus of quantitative methods is the fate and transport of materials in the environment. Topics include chemical equilibrium reactions, movement of admixtures in the environment, diffusion, turbulent mixing, and common computer models.
ENVI 591: Hydrogeology, 3 cr., Summer 2018
Hydrogeology includes general hydrology and a specific focus on groundwater and geochemical interactions. The course considers the movement of water on the surface (streams, wetlands, lakes, estuaries, etc.) and subsurface (porosity, permeability, flow paths, Darcy's Law, etc.), and air as a component of the water cycle. Concepts dealing with water management, pollution, remediation and prevention will be covered. Common computer models will also be considered.
Textbook (Summer 2018):