|Nicholson, Thomas - NUCLEAR REG. COMMISSION|
|Cady, Ralph - NUCLEAR REG. COMMISSION|
Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: May 8, 2006
Publication Date: May 23, 2006
Citation: Guber, A.A., Gish, T.J., Pachepsky, Y.A., Nicholson, T.J., Cady, R.E. 2006. A two-stage monitoring procedure for quantifying flow in variably-saturated heterogeneous soils. American Geophysical Union Joint Assembly, May 23-26, 2006, Baltimore, MD. CD-ROM, Paper No. H43D-04. Technical Abstract: Ground water recharge monitoring is an important component in assessing contaminant migration at sites where contaminants have been released at or near the surface. An innovative two-stage monitoring procedure that uses multiple soil moisture probes in a short duration first stage, followed by a smaller number of specially selected soil moisture probes at the second stage has been field tested. The first monitoring stage of relatively short duration focuses on confirming the temporal persistence of soil moisture patterns at selected depths, and on selecting the appropriate probes for best mimicking changes in average soil water content for each depth across the surveillance area. The second monitoring stage of longer duration uses only those selected probes to estimate the dynamics of the average soil water content across the surveillance area to understand the subsurface flow for estimating contaminant migration. This two-stage monitoring procedure was tested at a densely-instrumented watershed known as the U.S. Department of Agriculture's Agricultural Research Service (ARS) “OPE3” site in Beltsville, MD. The watershed has soil moisture multi-sensor capacitance probes installed at 24 locations to measure soil water content at depths of 10, 30, 50, 80, 120, 150, and 180 cm. Approximately two years of time series monitored soil moisture data were used to evaluate the needed duration for the first monitoring stage. For this site, one month of observations was found sufficient to evaluate the temporal persistence and to select the best probes that reproduced the changes in average water contents, and, after correction for persistence, the average water contents for each of the observation depths. The soil morphological discontinuities manifested themselves in deviations from persistence. The two-stage monitoring procedure provides for more efficient use of resources by selecting a reduced set of monitoring locations over a shorter monitoring period. The procedure greatly reduces the time duration and resources needed to monitor subsurface flow in variably saturated soils that influences contaminant migration to the water table. Further testing of this procedure in combination with application of model abstraction techniques is being pursued at the ARS watershed.