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Results of Field Studies at the Maricopa Environmental Monitoring Site, Arizona (NUREG/CR-5694)On this page: Download complete document The following links on this page are to documents in Adobe Portable Document Format (PDF). See our Plugins, Viewers, and Other Tools page for more information. For successful viewing of PDF documents on our site please be sure to use the latest version of Adobe. Publication InformationManuscript Completed: May 1999 Prepared by **Department of Soil, Water and Environmental Science Subcontractor: T. J. Nicholson, NRC Projeci Manager Prepared for *Currently at School of Civil and E Engineering AbstractThe purpose of this study was to evaluate issues related to alternative monitoring strategies for sites containing low level radioactive wastes. The study consisted of a theoretical evaluation of monitoring strategies and field studies. This NUREG reports on the field activities and the results of the field experiments. A field site, located at the Maricopa Agricultural Center (Maricopa, AZ) was designed for conducting controlled water flow and solute transport studies, and for testing the strengths and weaknesses of four monitoring strategies designated as 1) Monitoring Trench, 2) Monitoring Island, 3) Borehole Monitoring, and 4) Geophysical Monitoring. Field instrumentation was extensive, and designed to support alternative monitoring strategies. Two experiments were conducted at the site covering the time frame from Spring 1997 through Summer 1998. During Experiment 1, water was applied at an average flux of 1.85 cm d7' to the 50 m by 50 m field plot for 24 days, with bromide tracer added for the first 15 days. The water application period was followed by a redistribution period of 69 days. During Experiment 2, water was applied at an average rate of 1.97 cm d" for 33 days with a redistribution period of 177 days. Field experiments ended officially on July 1, 1998. Water movement across the plot was spatially variable during Experiment 1, due mostly to variability in the initial water content, and thus, the soil's hydraulic properties. The results of intrusive and non-intrusive instruments showed that 1) water movement in the western portion of the site was faster than the eastern portion; 2) a zone of more rapid water flow was observed near the northern and central areas of the plot, as confirmed using several types of instruments; and 3) the variability of water movement, as measured using a neutron probe, decreased with increasing depth. During Experiment 2, spatial variability of water movement was significantly reduced in surface soils (< 1.5 m), from a CV - 41.8 % to 4.7 % between Experiments 1 and 2, respectively. The reduced variability was observed because the flux-controlled water application led to more uniform hydraulic property fields, and thus, more uniform water movement. Most of the monitoring systems performed well during the field experiments. Though some data were lost (or considered unreliable) due to electrical problems with the AC power supply and corrosion of electrical connections, an extensive data set was compiled and found useful for comparing monitoring strategies. |
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