Comparison of Estimated Ground-Water Recharge Using Different Temporal Scales of Field Data (NUREG/CR-6653)

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Publication Information

Manuscript Completed: February 2000
Date Published: April 2000

Prepared by:
D. Timlin, J. Starr, USDA
R. Cady, T. Nicholson, NRC

U.S. Department of Agriculture
Agricultural Research Service
Beltsville Agricultural Research Center
Beltsville, MD 20705-2350

T. Nicholson, NRC Project Manager

Prepared for:
Division of Risk Analysis and Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code W6896

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Abstract

This study investigated field instrumentation [multi-sensor capacitance probes (MCP)] and analytical methods for estimating "real-time" infiltration and subsequent ground-water recharge and their attendant uncertainties. The research design was to apply a selected subset of existing field characterization data from the Beltsville Agricultural Research Center to technical issues identified by the NRC staff involving ground-water recharge estimates at nuclear facilities. The datasets allow comparisons of ground-water recharge estimates using near-continuous, water content measurements to recharge estimates based on less frequent water content observations (e.g. hourly or daily), intermittently measured piezometric data or analytical models. Drainage was underestimated by only using changes in water contents measured by MCP. Differences in water content did not always accurately represent fluxes when the system was at steady state. The estimate of net ground-water recharge decreased as measurement frequency decreased. The MCP data provided better estimates of recharge and timing than the piezometer data. Estimates of ground-water recharge were also compared to simulated recharge using a PNNL water budget model. The optimization of data in combination with a model can significantly reduce errors associated with using changes in water contents alone. A model optimized for hydraulic conductivity and moisture release parameters can calculate the fluxes using boundary conditions provided by the MCP and rainfall data. Further studies should move to larger scales (i.e., watershed) and lysimeters.