CAREER: Characterizing Preferential Water Flow in Laboratory and Field Soils with Gas Tracers

University Of Delaware, Newark DE

Investigators

Abstract

9984715 Imhoff While pesticides, herbicides and other chemicals and nutrients are intended for the root zone, leaching to groundwater or nearby surface water often leads to environmental contamination. It has been hypothesied that spatial variability in water fluxes, or preferential flow, is the cause of the relatively fast transport to the groundwater observed in many field soils. This same process is thought to be significant in landfills as well where it affects the distribution of leachate and overall rates of biological degradation and methane gas production. While preferential flow has been recognized as an important mechanism influencing contaminant transport, its characterization has been hampered by a lack of adequate field tools for quantifying this process. The research proposed will examine the utility of gas phase tracers in the laboratory and in field experiments. Preferential water flow will be quantified by fitting parameters to a model describing the transport of a nonreactive water tracer. Independent of the water tracer test, gas phase tracers will be used to determine the ratio of the gas/water interfacial area to the volumetric water content. It is hypothesied that the ratio of these parameters determined from the gas tracers can be correlated with fitted parameters to the model for transport of the water tracer. If successful, gas tracers may be used to quantify the degree of preferential flow faster and at less cost than current methods, thereby providing a valuable tool for characterizing preferential flow in field soils and of leachate in landfills. The educational objectives of this project are to develop active-learning or student-centered teaching methods involving problem-based learning, undergraduate tutors, undergaduate and graduate student research and a web-based teaching module that will strengthen the PI's pedagogical style and positively influence the teaching styles of other faculty in the department. Student-centered learning will be incorporated in two undergraduate courses over a four-year period. Their effectiveness will be determined through surveys and interviews using assessment tools selected from those recommended by the University of Delaware Institute for Tranforming Undergraduate Education. In this way, quantitative data on the benefits and/or problems with these teaching methods in an environmental engineering curriculum can be made available to other faculty within the engineering community. One aspect of the educational plan is to involve undergraduate and graduate students in the process of discovery through scientific research. Students will actively participate in the above research on preferential flow, a critical process that affects the transport of agricultural chemicals in the subsurface. ***