Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 10, 2011
Publication Date: August 3, 2011
Citation: Gish, T.J., Guber, A.K., Pachepsky, Y.A. 2011. Monitoring contaminant strategies: tools, techniques, methodologies and model approaches [abstract]. Workshop on Engineering Barrier Performance Related to low-level Radioactive Waste, Decommissioning, and Uranium Mill Trailings Facilities. p. 96-98. Technical Abstract: A century-long history of experiments on solute transport in soils has resulted in a wide range of experimental setups and procedures, as well as methods for interpreting observations which has led to considerable ambiguity regarding monitoring approaches. This presentation will focus on results and lessons learned from three shallow chemical transport studies carried out at the USDA-ARS Beltsville, Maryland research facility. A hybrid monitoring and model approach was proposed and tested to demonstrate it’s applicability for quantifying potential and actual contaminant release from sites germane to US NRC operations. Soil moisture, soil water potential, conservative tracer concentrations in groundwater, groundwater levels, and weather data, along with ground-penetration radar surveys, electric resistivity monitoring, and dilution tests complemented borehole log data and laboratory hydraulic measurements to characterize soil heterogeneity. Like the monitoring procedure, no single chemical transport model, regardless of complexity can describe field-scale transport. In this regard model abstract techniques were used with a sequence of model simplifications based on the HYDRUS software family to evaluate chemical transit times. The invoked series of model abstractions showed the important role of subsurface heterogeneity in the vadose zone and groundwater, and substantial improved the conceptualization of the subsurface and chemical transport behavior. For this site, data and model analysis indicated that field experimental setups should address at least two types of heterogeneities: 1) differences in water mobility in different parts of the soil; and 2) the effects of restricting layers and the capillary fringe on lateral transport.