1a.Objectives (from AD-416)
The objective of this research effort is to test, confirm and demonstrate the practicality of various model abstraction techniques for characterizing and simulating subsurface flow and contaminant transport through soils using a range of simple to complex analytical and numerical models at the watershed scale.

1b.Approach (from AD-416)
Identify and review appropriate model abstraction techniques for hierarchical application of transport modeling for specific soil and contaminant properties and particular environmental conditions at watershed scale; test and confirm the appropriateness of the model abstraction approach through comparisons with conventional complex flow and transport models.

3.Progress Report
This report documents research conducted under a reimbursable agreement between ARS and the U.S. Nuclear Regulatory Commission. Additional details of the research can be found in the report for the parent project 1265-12630-003-00D "Fate and transport of manure-borne pathogenic microorganisms." The research consisted of data collection, data analysis, and modeling in order to develop a case study for using model abstraction techniques at the watershed scale. Model abstraction is the methodology for reducing the complexity of a simulation model while maintaining the validity of the simulation results with respect to the question that the simulation is being used to address. Model abstraction can help NRC determine whether a simple model can be used that is easy to understand and easily communicated to regulators, stakeholders, and the general public, while at the same time adequately representing their site. The balance between model complexity and model accuracy is extremely important in development of viable models of pathogen fate and transport. An exhaustive dataset on soil water time series was analyzed to determine whether the temporal stability could be used to improve the soil water monitoring. A new ground-penetration radar dataset was analyzed to define the topography of the subsurface low permeable layer. The new vadose zone monitoring site was equipped with replicated soil water capacitance probes and tensiometers. The GMS-FEMWATER software was used to define the placement of new wells for multi level groundwater sampling after the planned tracer application. The HYDRUS software was applied to simulate the preliminary tracer application experiment with the goal of assuring the possibility to calibrate both flow and transport models from coupled observations with the available instrumentation. The procedures of estimating average infiltration loss were revisited to assure the integrity of data available to run the field scale model.

The progress of the work has been monitored by monthly teleconferences, three meetings with the NRC technical advisory group, and weekly group meetings.